Ascending And Descending Tracts Of Spinal Cord

Spinal Cord Question And Answers

Question 1. Write a short note on laminar organization in spinal cord.
Answer:

Laminar organization in spinal cord

Spinal Cord Spinal Gray Matter

  • In thick section, neurons of the spinal cord appear to have a laminar arrangement
  • Starting from tip of dorsal horn towards the vertical horn ten layers are recognized
  • These are as follows:
  1. Lamina 1: Corresponds to posteromarginal nucleus
  2. Lamina 2: Corresponds to substantia gelatinosa
  3. Lamina 3 and 4: Corresponds to nucleus proprius
  4. Lamina 5 and 6: Corresponds to the base of dorsal column
  5. Lamina 7: Occupies the territory between dorsal and ventral horns and contains cells that function as interneurons. Nucleus dorsalis, intermediolateral, intermediomedial are clear cell columns recognized within this lamina
  6. Lamina 8: Corresponds to ventral horn in thoracic segments
  7. Lamina 9: Includes lateral group of nuclei of the ventral horn, supply skeletal muscles of limb
  8. Lamina 10: Surrounds the central canal and contains decussating axons, neuroglia, and some neurons with interneuron properly.

Question 2. Write a short note on tracts of the spinal cord.
Answer:

Tracts of the spinal cord

Spinal Cord Cross-section Of Spinal Cord To Show Ascending And Descending Tracts In White Matter

  • A collection of nerve fibers that connects two masses of gray matter within the central nervous system (CNS) is called a tract
  • These are ascending and descending tracts, and named after gray matter connected by them.

Spinal Cord Descending Tracts: These include

  • The pyramidal tract/corticospinal tracts
  • Descends from cerebral cortex to spinal cord and consists of:
    • Lateral corticospinal tract
    • Anterior corticospinal tract.
  • The extrapyramidal tracts include:
    • Rubrospinal tract
    • Medial reticulospinal tract
    • Lateral reticulospinal tract
    • Olivospinal tract
    • Vestibulospinal tract
    • Tectospinal tract.
  • Pyramidal tracts
    • These are formed by axons of pyramidal cells lying in the motor area of cerebral cortex
    • From the base the first pass through the internal capsule, midbrain, pons, and medulla
    • At the lower border of medulla, 80% of fiers cross to opposite side, and is called as pyramidal decussation and enter the lateral column and descends on lateral corticospinal tract
    • The fibers which do not cross enter the anterior column and descend as anterior corticospinal tract.

Spinal Cord Course Of The Corticospinal Tracts

Spinal Cord Indirect Pathways Through Which The Cerebral Cortrex May Influence The Spinal Cord

Spinal Cord Ascending Tracts: These include the following

  • Lateral spinothalamic tract
  • Anterior spinothalamic tract
  • Fasciculus gracilis
  • Fasciculus cuneatus
  • Anterior spinocerebellar tract
  • Posterior spinocerebellar tract
  • Spino-olivary tract
  • Spinotectal tract.

Spinal Cord Multiple Choice Question And Answers

Question 1. All of the following are descending tracts except:

  1. Anterior corticospinal tract
  2. Rubrospinal tract
  3. Spino-olivary tract
  4. Olivospinal tract

Answer: 3. Spino-olivary tract

Question 2. All of the following statements about the laminar organization of spinal cord is correct except:

  1. Lamina 1 corresponds to posteromarginal sulcus
  2. Lamina 7 includes the intermediomedial, inter mediolateral and dorsal nuclei
  3. Lamina 5 corresponds to the neck of the dorsal gray column
  4. Lamina 8 occupies most of the dorsal horn in thoracic segments.

Answer: 4. Lamina 8 occupies most of the dorsal horn in thoracic segments.

Brainstem Question And Answers

Brainstem Question And Answers

Question 1. Write a short note on the transverse section of medulla at level of decussation of the pyramid.
Answer:

The transverse section of medulla at level of decussation of the pyramid

Resemble the transverse section of the spinal cord and pass through inferior half of medulla.

Brainstem Transverse Section Of Medlla Oblongata At The Level Of Phramidal Decussation

Abbreviation: MLF—Medial longitudinal fasciculus

Decussation Of Pyramid Gray Matter

  • Pyramidal fiers separate anterior horn from the central gray matter
  • Anterior horn forms the spinal nucleus of the accessory nerve
  • Central gray matter is pushed backward
  • Nucleus gracilis and cuneatus are continuous with central gray matter
  • Central gray matter is continuous with the nucleus of spinal tract of trigeminal nerve.

Decussation Of Pyramid White Matter

  • Pyramids anteriorly
  • Decussation of pyramidal tracts
  • Fasciculus gracilis and cuneatus occupy the posterior column
  • Other features of white matter is similar to the spinal cord.

Question 2. Write a short note on the transverse section of the medulla at the level of sensory decussation.
Answer:

The transverse section of the medulla at the level of sensory decussation

The section passes through the middle of the medulla and following features are seen.

Brainstem Transverse Section Of Medlla Oblongata At The Level Of Sensory Decussation

Abbreviation: MLF—Medial longitudinal fasciculus

Sensory Decussation Gray Matter

  • Nucleus gracilis and cuneatus are larger and separate from central gray matter
  • Accessory cuneate nucleus which relays unconscious proprioceptive fiers from upper limbs
  • Nucleus of the spinal tract of the trigeminal nerve is separated from the central gray matter
  • Lower part of inferior olivary nucleus seen
  • Central gray matter contains a hypoglossal nucleus, dorsal nucleus of vagus, and nucleus of tractus solitarius.

Sensory Decussation White Matter

  • Nucleus gracilis and cuneatus give rise to internal arcuate fibers which cross to the opposite side and form a band of fibers called medial lemniscus
  • Pyramidal tracts anteriorly
  • Medial longitudinal bundle posterior to the medial lemniscus
  • Spinocerebellar, lateral spinothalamic tracts in anterolateral area.

Question 3. Write a short note on the transverse section of the medulla at the level of olives.
Answer:

The transverse section of the medulla at the level of olives

The section that passes through the floor of fourth ventricle shows the following features.

Olives Gray Matter: Nuclei of cranial nerves

  • Hypoglossal nucleus
  • Dorsal nucleus of vagus
  • Nucleus of tractus solitarius
  • Inferior and medial vestibular nuclei.

Brainstem Transverse Section Of The Open Part Of Medlla Oblongata At The Level Of Inferior Olive

Abbreviation: MLF—Medial longitudinal fasciculus

  • The nucleus ambiguity lie deep to the reticular foramen
  • The dorsal and ventral cochlear nuclei lie on the surface of the inferior cerebellar peduncle
  • The nucleus of spinal tract of trigeminal nerve
  • The inferior olivary nucleus is the largest mass of gray matter and appear like crumpled purse
  • The arcuate nucleus lies anteromedial to the pyramidal tract.

Olives White Matter

  • Inferior cerebellar peduncle in the posterolateral part
  • Olivocerebellar fibers
  • Stria medullaris is the floor of the fourth ventricle
  • Ascending tracts
  • Emerging fiers of 9, 10, 11 nerves.

Question 4. Write a short note on the transverse section of pons at the level of facial colliculus.
Answer:

The transverse section of pons at the level of facial colliculus

The section passes through a lower level of pons and the following features are seen.

Brainstem Transverse Section Of Pons At The Lower Level

Abbreviation: MLF—Medial longitudinal fasciculus

Facial Colliculus Gray Matter

  • Abducent nerve nucleus lie beneath facial colliculus
  • Motor nerve nucleus of facial nerve lies ventrolateral to abducent nucleus
  • Superior salivatory, inferior salivatory and lacrimatory nucleus lie medial to motor nuclei of facial nerve
  • The nucleus of tractus solitarius lies lateral to superior salivatory nucleus
  • Vestibular nucleus lie beneath vestibular area
  • Dorsal and ventral cochlear nuclei lie dorsal and ventral to inferior cerebellar peduncle
  • The spinal nucleus of trigeminal nerve lie anteromedial to inferior cerebellar peduncle.

Facial Colliculus White Matter

  • Trapezoid body present posterior to basilar part of pons
  • Medial lemniscus in the anterior part of tegmentum
  • Spinal lemniscus lying lateral to medial lemniscus
  • Medial longitudinal bundle occupying paramedian position
  • Tectospinal tract lying ventral to median longitudinal bundle
  • Spinal tract to trigeminal nerve lying lateral and dorsal to motor nucleus of facial nerve.

Question 5. Write a short note on transverse section through the upper part of pons.
Answer:

Transverse section through the upper part of pons

This section passes through the trigeminal nuclei and the following features are seen.

Brainstem Transverse Section Of Pons At The Upper Level

Abbreviation: MLF—Medial longitudinal fasciculus

Upper Part Of Pons Gray Matter

  • The motor nucleus of trigeminal nerve is situated beneath the lateral part of the fourth ventricle
  • The sensory nucleus of the trigeminal nerve is present lateral to motor nucleus of facial nerve.

Upper Part Of Pons White Matter

  • Consists of ascending tracts as in lower part of pons
  • Lateral lemniscus is well-formed
  • Spinal lemniscus lie in between medial and lateral reminisce
  • Trigeminal lemniscus is seen between medial and spinal reminisce
  • Superior cerebellar peduncle lie dorsolateral to fourth ventricle
  • The medial longitudinal bundle is seen.

Question 6. Write a short note on transverse section of midbrain at the level of inferior colliculus.
Answer:

Transverse section of midbrain at the level of inferior colliculus

The section of midbrain at the level of inferior colliculus shows the following features.

Brainstem Transverse Section Of Midbrain At The Level Of Inferior Colliculus

Inferior Colliculus Gray Matter: The central gray matter contains the following

  • Trochlear nerve nucleus in vertical part
  • The mesencephalic nucleus of trigeminal nerve in lateral part.
  • Nucleus of inferior colliculus, an ovoid mass of gray matter below inferior colliculus
  • Substantia nigra.

Inferior Colliculus White Matter

  • The decussation of superior cerebellar peduncles in the central part
  • Arrangement of reminisce to form curved compact band in ventral part
  • Medial longitudinal fasciculus (MLF) lies in the side of medial plane ventral to trochlear nerve nucleus.

Question 7. Write a short note on transverse section of midbrain at the level of the superior colliculus.
Answer:

Transverse section of midbrain at the level of the superior colliculus

The section shows gray and white matters with the following features.

Brainstem Transverse Section Of Midbrain At The Level Of Superior Colliculus

Superior Colliculus Gray Matter: The central gray mater containing

  • Oculomotor nucleus in ventral part
  • Mesencephalic nucleus as in the lower part of midbrain.
  • Nucleus of superior colliculus
  • Pretectal nucleus lying deep to the superolateral part of superior colliculus
  • Red nucleus presents vertical to third nerve nucleus.

Superior Colliculus White Matter

  • Decussation of fibers from superior colliculus forming dorsal tegmental decussation
  • Decussation of fibers arising from red nuclei forming ventral tegmental decussation
  • MLF lying ventrolateral to oculomotor nerve.

Brainstem Multiple Choice Question And Answers

Question 1. The transverse section of the medulla at the level of olives shows all of the following except:

  1. Hypoglossal nucleus
  2. Nucleus of tractus solitarius
  3. Nucleus cuneatus
  4. Nucleus ambiguous

Answer: 3. Nucleus cuneatus

Question 2. All of the following nuclei are found in pons at the level of facial colliculus except:

  1. Abducent nucleus
  2. Motor nucleus of trigeminal nerve
  3. Motor nucleus of the facial nerve
  4. Cochlear nuclei

Answer: 2. Motor nucleus of trigeminal nerve

Cerebellum Question And Answers

Cerebrum Question And Answers

Question 1. Write a note on the lobes and external surfaces of cerebral hemispheres.
Answer:

Lobes and external surfaces of cerebral hemispheres

Cerebrum Lateral Aspect Of Cerebral Hemisphere To Show Borders, Poles, And Lobes

Cerebrum Inferior Aspect Of Cerebral Hemisphere To Show Borders, Poles, And Surfaces

The external features of the cerebral hemispheres include:

  1. Poles
  2. Surfaces
  3. Borders
  4. Sulci and Gyri.

1. Poles: Each cerebral hemisphere presents the following poles

  • The frontal pole: The anterior end of the hemisphere and is rounded
  • The occipital pole: The posterior end of the hemisphere and is more pointed in shape
  • The temporal pole: The anterior end of the temporal lobe.

2. Surfaces: Each cerebral hemisphere consists of the following surfaces

  • The superolateral surface: The most extensive surface and is convex in shape
  • The medial surface: The flat and vertical surface presents a C-shaped cut surface of the corpus callosum
  • The inferior surface: The irregular surface corresponds to the floor of the anterior and middle cranial fossa and is divided into anterior and posterior part by stem of the lateral sulcus.

3. Borders: Each cerebral hemisphere presents the following borders

  • The superomedial border which separates the superolateral surface from the medial surface
  • The superciliary border which is present at the junction of superolateral and orbital surfaces
  • The inferolateral border which separates the superolateral surface from the tentorial surface
  • The medial orbital border which separates the medial surface from the orbital surface
  • The inferomedial border which surrounds the cerebral peduncle
  • The medial occipital border separates the medial surface from the tentorial surface.

4. Sulci and Gyri 

  • The cerebral cortex is thrown into a complex series of tortuous folds called gyri or convolution
  • The grooves between the gyri are known as sulci
  • These gyri are responsible for the increase in the surface area of the cortex.

Lobes of Cerebral Hemisphere

The superolateral surface of each hemisphere is divided into four lobes by three main sulci known as central, lateral, and parietooccipital. The lobes are as follows:

  1. Frontal lobe
  2. Parietal lobe
  3. Temporal lobe
  4. Occipital lobe.
  • The central sulcus begins at the superomedial border of the hemisphere about 1 cm behind the midpoint of the frontal and occipital poles. It runs obliquely downwards and forwards and ends a little above the posterior ramus of the lateral sulcus
  • The lateral sulcus of Sylvius consists of a stem and three rami. The stem begins as a deep cleft on the inferior surface of the cerebral hemisphere at the anterior perforated substance and extends laterally to reach the superolateral surface. On the superolateral surface it divides into 3 rami:
  1. Anterior horizontal rami
  2. Anterior ascending rami
  3. Posterior rami.
  • The parieto-occipital sulcus is present at the medial surface and begins at the midpoint of the calcarine sulcus and passes upwards and slightly backward to cut the superomedial border of the hemisphere
  • The calcarine sulcus is present on the medial surface and begins as a deep fissure, a little below the posterior end of the corpus callosum, the splenium, and follows an arched course with convexity directed upwards to the occipital pole
  • The division is completed by drawing an imaginary line joining the parieto-occipital sulcus to the occipital notch and another line continuing backward from the posterior ramus of the lateral sulcus to meet the first line
  • The frontal lobe lies anterior to the central sulcus and above the posterior ramus of the lateral sulcus
  • The parietal lobe lies behind the central sulcus and in front of the first imaginary line and below by the posterior ramus of lateral sulcus and a second imaginary line
  • The temporal lobe lies below the posterior ramus of the lateral sulcus and second imaginary line
  • The occipital lobe lies behind the vertical line joining the parieto-occipital sulcus and the occipital notch.

Insula (Central Lobe)

  • It is a hidden portion of the cerebral cortex in the floor of the lateral sulcus
  • It is triangular in shape and surrounded all around by a sulcus, the circular sulcus, except anteriorly at its apex called the limen insulae which is continuous with anterior perforated substance

Cerebrum Simplified Presentation Of Sulci And Gyri On The Superolateral Surface Of The Cerebral Hemisphere

Cerebrum Simplified Presentation Of Sulci And Gyri On The Medial Aspect Of The Cerebral Hemisphere

Cerebrum Structures To Be Seen On The Inferior Aspect Of The Cerebrum

The insula is divided into two regions by the central sulcus:

  1. Anterior
  2. Posterior.
  • The anterior region presents 3–4 short gyri called gyri breviate and the posterior region presents 1–2 long gyri called gyri longa
  • The insula is overlapped by the adjacent cortical areas called opercula and they include the frontal, frontoparietal, and temporal opercula
  • The superior surface of the temporal operculum presents the anterior and posterior transverse temporal gyri.

Abbreviations: a = Pars orbitalis; b = Pars triangularis; c = Pars opercularis

Question 2. Write a note on sulci and gyri of brain.
Answer:

The sulci and gyri of the brain can be studied under the following headings:

  1. Sulci and gyri on the superolateral surface
  2. Sulci and gyri on the medial surface
  3. Sulci and gyri on the inferior surface.

1. Sulci and Gyri on the Superolateral Surface

  • In the Frontal Lobe
    • The prefrontal sulcus runs downwards and forwards parallel and little anterior to the central sulcus
    • The area between the central and precentral sulci is called the precentral gyrus
    • Anterior to the precentral sulcus there are two sulci called superior and inferior frontal sulci which run horizontally and divide the region in front of the precentral sulcus into superior, middle, and inferior frontal gyri

The anterior and ascending rami of the lateral sulcus divide the inferior frontal gyrus into three parts:

  1. Pars orbitalis: Th part below the anterior ramus
  2. Pars triangularis: Th part between anterior and ascending rami
  3. Pars opercularis: Th part posterior to the ascending ramus.
  • In the Parietal Lobe
    • The postcentral sulcus runs downwards and forwards a little behind and parallel to the central sulcus and the area between these two sulci is known as postcentral gyrus
    • The rest of the parietal lobe is divided into superior and inferior parietal lobules by an intraparietal sulcus.
  • In the Temporal Lobe
    • In the temporal lobe, two sulci run parallel to the posterior ramus of lateral sulcus and these are known as superior and inferior temporal sulci and divide the temporal lobe into superior, middle, and inferior temporal gyri.
    • The superior surface of the superior temporal gyrus presents two transverse temporal gyri.
  • In the Occipital Lobe: The occipital lobe presents three short sulci
  1. Lateral occipital sulci
  2. Transverse occipital sulci
  3. Lunate sulcus.

2. Sulci and Gyri on the Medial Surface: The sulci and gyri of the medial surface are as follows:

  • Cingulate sulcus: Th most prominent sulcus which is parallel to the upper convex margin of the corpus callosum. Anteriorly it ends below the genu of corpus callosum and posteriorly it turns upwards to reach the superomedial border of the hemisphere just behind the upper end of the central sulcus
  • Callosal sulcus: It separates the cingulate gyrus from the corpus callosum
  • The part of the medial surface between the cingulate sulcus and the superomedial border of the hemisphere is divided by a short sulcus ascending from the cingulate sulcus above the middle of the trunk of the corpus callosum into two:
    1. The paracentral lobule: A small part around the upper part of the central sulcus
    2. Medial frontal gyrus: A large medial part.
  • The posterior part of the medial surface behind the paracentral lobule has two main sulci
    • The calcarine sulcus: The small region between the splenium and calcarine sulcus is called the isthmus
    • The parieto-occipital sulcus: The triangular area between the posterior part of the calcarine sulcus and the parieto-occipital sulcus is called cuneus
    • The quadrangular area between the parietooccipital sulcus and paracentral lobule is called the precuneus.
  • A small sulcus just above and parallel to the splenium is called supraspinal sulcus and separates the precuneus from cingulate gyrus.

3. Sulci and Gyri on the Inferior Suface

  • On the orbital part of inferior surface:
    • Olfactory sulcus: A straight sulcus that runs anteroposteriorly close to the medial border of the orbital surface. The area medial to this sulcus is called gyrus rectus.
    • Orbital sulcus: It is an irregular, H–shaped sulcus which divides the rest of the orbital surface to the following gyri:
      • Anterior orbital gyri
      • Posterior orbital gyri
      • Medial orbital gyri
      • Lateral orbital gyri
  • On the tentorial part of the inferior surface:
    • The surface consists of two major sulci that run anteroposteriorly. They are
      • Collateral sulcus: The medial one
      • Occipitotemporal sulcus: The lateral one
    • Posteriorly the collateral sulcus is parallel to the calcarine sulcus and the area between the two is known as lingual gyrus
  • The lingual gyrus is continuous anteriorly with the parahippocampal gyrus. The anterior end of the parahippocampal gyrus is hook-like and is called as the uncus
  • Posteriorly the parahippocampal gyrus is continuous with the cingulate gyrus through the isthmus
  • The area between the occipitotemporal sulcus and the collateral and rhinal sulcus is known as medial occipitotemporal gyrus
  • The area lateral to the occipitotemporal sulcus is called lateral occipitotemporal gyrus.

Question 3. Write a short note on the medial geniculate body.
Answer:

The medial geniculate body

Oval elevation present below the pulvinar of thalamus of thalamus and lateral to superior colliculus.

Cerebrum Location Of The Medial And Lateral Geniculate Bodies

Medial Geniculate Body Connections

  • Afferents:
    • Lateral lemniscus
    • Fibers from both inferior colliculus.
  • Effects: Give rise to auditory radiation joining to auditory area of cortex through sublentiform part of the internal capsule.

Medial Geniculate Body Function: Act as relay station in pathway of auditory impulses to cerebral cortex.

Question 4. Write a short note on lateral geniculate body.
Answer:

Lateral geniculate body

Small oval elevation present anterolateral to medial geniculate body, below the thalamus. It is connected to superior colliculus by the superior brachium.

Lateral Geniculate Body Structure

  • Six layered
  • Layer 1, 4, and 6 receive contralateral optic fibers
  • Layers 2, 3, and 5 receive ipsilateral optic fibers.

Lateral Geniculate Body Connection

  • Afferent: Optic tract
  • Efferent: Give rise to optic radiation going to visual area of cortex through retro lentiform part of the internal capsule.

Lateral Geniculate Body Function: It is the last relay station in the visual pathway to the occipital cortex.

Question 5. Write a note on the hypothalamus.
Answer:

Hypothalamus

It is a part of the diencephalon which lies below thalamus.

Cerebrum Main Hypothalamic Nuclei As Seen From The Medial Aspect

Hypothalamus Boundaries: The boundaries of the hypothalamus include

  • Anteriorly: Lamina terminalis
  • Posteriorly: Subthalamus
  • Inferiorly: Tuber cinereum, infundibulum, mammillary body
  • Superiorly: Thlamus
  • Laterally: Internal capsule
  • Medially: Cavity of 3rd ventricle.

Hypothalamus Subdivisions: It is divided anteroposteriorly into the following

  1. Preoptic region
  2. Supraoptic region
  3. Tuberal region
  4. Mammillary region.

1. Preoptic Region: It lies anterior to the hypothalamus between the optic chiasma and anterior commissure.

2. Supraoptic Region: The region above the optic chiasma.

3. Tuberal Region

  • It includes tuber cinereum, infundibulum, and surrounding area
  • The tuber cinereum is bounded caudally by mammillary bodies and rostrally by optic chiasma
  • The infundibulum connects the pituitary with tuber cinereum
  • The tuber cinereum around the base of the infundibulum is raised to form median eminence.

4. Mammillary Region: It includes the mammillary bodies and the area around it.

Hypothalamic Nuclei: The hypothalamus consists of numerous cell groups known as hypothalamic nuclei which are present in different regions as follows:

  • Preoptic region: Preoptic nucleus
  • Supraoptic region: Supraoptic nucleus, anterior nucleus, paraventricular nucleus
  • Tuberal region: Infundibular nucleus, ventromedial and dorsomedial nuclei
  • Mammillary region: Posterior nucleus and mammillary nuclei.

Cerebrum Hypothalamic Regions And Nuclei

Connections Of Hypothalamus

Cerebrum Main Connections Of The Hypothalamus

The main connections of the hypothalamus are as below

  • Hypothalamic hypophyseal tract
    • Formed by the axons of supraoptic and paraventricular nuclei which run in the pituitary stalk to reach the posterior pituitary
    • It transports vasopressin and oxytocin produced in the supraoptic nucleus and paraventricular nucleus to the posterior pituitary
  • Though Hypothalamo hypophyseal portal system
    • The axons of tuberal nuclei reach median eminence to deliver their neurosecretory material to the hypothalamohypophyseal portal system of blood vessels
    • The secretions control the secretion of hormones from the anterior pituitary.
  • Mammillothalamic tract: It connects mammillary body to anterior nucleus of the thalamus
  • Hypothalamospinal tract: Formed by synapse of long axons from thalamus with the preganglionic sympathetic cells in lateral horns of thoracic and upper 2 lumbar spinal segments and with the preganglionic para sympathetic cells in lateral horns of S2, S3, and S4 spinal segments.

Hypothalamus Functions: The various functions of hypothalamus include the following

  • Autonomic control
  • Endocrine control
  • Neurosecretion
  • Regulation of water and food intake
  • Emotional expression
  • Sexual behavior and reproduction
  • Temperature regulation
  • Regulation of circadian rhythm.

Question 6. Write a short note on basal ganglia.
Answer:

Basal ganglia

They are large subcortical masses of grey matter present inside the white mater in the basal part of the cerebral hemisphere.

Cerebrum Coronal Section Of Brain Passing Through Anterior Perforated Substance

Cerebrum The Corpus Striatum Viewed From The Lateral Aspect

  • Anatomically it includes:
    • Corpus striatum
    • Claustrum
    • Amygdaloid body.
  • Functionally it also includes:
    • Substantia nigra
    • Red nucleus
    • Subthalamus.

Corpus Striatum

  • It is located lateral to the thalamus
  • It is divided into a caudate nucleus and lentiform nucleus by internal capsule and the fibers of the anterior end is connected to the internal capsule giving a striated appearance hence the name corpus striatum.

Caudate Nucleus

  • It is a large comma shaped mass of grey matter which surrounds thalamus.
  • Its convexity projects into the cavity of the lateral ventricle
  • It is divided into:
    • Head: Th rounded anterior part in front of interventricular foramen.
    • Body: It is actually the tapered portion of the continuation of head
    • Tail which merges with the amygdaloid body.

Lentiform Nucleus

  • It is a large lens shaped mass of grey matter beneath the insula lateral to internal capsule.
  • It is divided into:
    • Putamen: The outer dark part
    • Globus pallidus: The inner lighter part
  • Putamen is similar to the caudate nucleus and contains densely packed small cells.
  • Globus pallidus consists of large motor cells.
  • The globus pallidus is termed paleostriatum and the caudate nucleus and putamen is termed the neostriatum.

Claustrum: It is a thin saucer-shaped mass of grey matter situated in between putamen and insula.

Amygdaloid Body

  • It is an almond-shaped mass of grey matter in temporal lobe present near the inferior horn of the lateral ventricle
  • The fibers from the amygdaloid body form the stria terminalis which form the main efferent tract of the amygdaloid body
  • The striae terminalis follow the inner curve of the caudate nucleus and terminate into septal area, anterior perforated substance, and anterior hypothalamic nuclei.

Substantia Nigra

  • It is a curved pigmented band of grey matter located between crus cerebri and tegmentum
  • It consists of deeply pigmented nerve cells that contain melanin and iron.

Red Nucleus

  • It is a cigar-shaped mass of grey matter
  • It is located in the tegmentum ventral to 3rd nerve nucleus and dorsomedial to substantia nigra
  • It is an important nucleus in the extrapyramidal system.

Subthalamus

  • It is a small nucleus in the ventral part of the thalamus
  • It is located caudal to the lateral half of thalamus and inferior to globus pallidus
  • It is separated from the thalamus by a small nucleus known as the zona insert.

Basal Gangila Functions

  • It is mainly involved in organizing and coordinating motor movements
  • It decreases muscle tone and inhibit unwanted muscular activity
  • It also controls reflex muscular activity.

Basal Ganglia Applied: Lesions of basal ganglia can result in parkinsonism, chorea, athetosis, and ballismus.

Question 7. Write a note on the corpus callosum.
Answer:

Corpus callosum

It is the largest commissure of the brain and consists about 100 million fiers.

Cerebrum Course Of Commissural Fibers Through Genu, Trunk, And Splenium Of Corpus Callosum

Corpus Callosum Parts: It is divided into the following four parts:

  1. Genu
    • The thick curved anterior extremity which lies 4 cm behind the frontal pole
    • The fibers of genu curve forward on either side of frontal lobes to form fork-like structure called forceps minor.
  2. Rostrum: It is the thin prolongation of genus which joins the lamina terminalis.
  3. Trunk: It is the main part of corpus callosum between genu and splenium.
  4. Splenium
    • It is the massive posterior extremity of corpus callosum which lies about 6 cm in front of the occipital lobe
    • Its fibers connect the parietal, temporal, and occipital lobes of two cerebral hemispheres
    • The fibers connecting the occipital lobe curves backward on either side above the calcarine sulcus and form a large fork-like structure known as forceps major.

Corpus Callosum External Features

  • It forms a massive arched interhemispheric bridge and connects the medial surfaces of two cerebral hemispheres
  • In the sagittal section of cerebrum, it is seen as a C-shaped mass of white fibers forming roof of the lateral ventricle
  • The inferior aspect of corpus callosum is concave and is attached to the convex superior aspect of the fornix by septum pellucidum.

Corpus Callosum Functions: It is mainly responsible for bilateral responses and learning process which is achieved through interhemispheric transfer of information.

Question 8. Write a note on the internal capsule.
Answer:

Internal capsule

Cerebrum Location And Constituent Fibers Of Internal Capsule

Abbreviations: LL = Lower limb; UL = Upper limb; MGB = Medial geniculate body; LGB = Lateral geniculate body

Cerebrum Coronal Section Through A Cerebral Hemisphere To Show The Location Of Internal Capsule

  • It is a compact bundle of projection fibers between the thalamus and caudate nucleus on the medial side and lentiform nucleus on lateral side
  • It consists of ascending and descending fibers that connects the spinal cord and brain stem to the cerebral cortex
  • The afferent fibers pass from the thalamus to the cerebral cortex and the efferent fibers pass from the cerebral cortex to cerebral peduncle of midbrain.

Internal Capsule Parts

  • In horizontal section of cerebral hemisphere, the internal capsule appears as a V–shaped bundle of white fiers with concavity directed laterally
  • It is divided into the following parts:
  1. Anterior limb
    • It is present between head of the caudate nucleus and anterior part of lentiform nucleus.
    • The constituent motor fiers include corticopontine fibers and sensory includes anterior thalamic radiation.
  2. Genu
    • It is the bend between anterior and posterior limbs and the concavity faces laterally.
    • It consists of corticopontine fibers, corticonuclear and corticospinal fibers as motor fibers, and superior thalamic radiation as sensory fibers.
  3. Posterior limb
    • It is present between the thalamus and the posterior part of the lentiform nucleus.
    • It consists of corticopontine fibers, corticospinal and corticofugal fibers as constituent motor fibers, and superior thalamic radiation as sensory fibers
  4. Retrolentiform part
    • It is present behind the lentiform nucleus
    • It consists of corticopontine fibers and posterior thalamic radiation as motor and sensory fields respectively
  5. Sublentiform part
    • It is present below the lentiform nucleus
    • It consists of corticopontine fibers as motor fibers and inferior thalamic radiation as sensory fibers.

Cerebrum Fibers Passing Through The Internal Capsule

Internal Capsule Functions: The sensory and motor fibers of internal capsule is responsible for sensory and motor innervation of the opposite side of the body.

Internal Capsule Applied: Small lesions in the internal capsule can produce widespread paralytic effects and sensory loss in the opposite half of body due to the presence of dense motor and sensory fibers.

Cerebrum Multiple Choice Question And Answers

Question 1. Which of the following structures represents the submerged portion of the cerebral cortex?

  1. Frontoparietal operculum
  2. Insula
  3. Hippocampus
  4. Temporal operculum

Answer: 2. Insula

Question 2. The paracentral lobule is located on:

  1. Medial surface of the cerebral hemisphere
  2. The superolateral surface of the cerebral hemisphere
  3. The tentorial surface of the cerebral hemisphere
  4. Orbital surface of the cerebral hemisphere

Answer: 1. Medial surface of the cerebral hemisphere

Question 3. All of the following are examples of commissural fibers except:

  1. Corpus callosum
  2. Interthalamic adhesion
  3. Anterior commissure
  4. Habenular commissure

Answer: 2. Interthalamic adhesion

Question 4. Which of the following structures consists of both projection and commissural fibers?

  1. Internal capsule
  2. Pyramid
  3. Cerebral fornix
  4. Crus cerebri

Answer: 3. Cerebral fornix

Question 5. The area between the parieto-occipital and calcarine sulcus on the medial surfaces of the cerebral hemisphere is known as:

  1. Paracentral lobule
  2. Cuneus
  3. Precuneus
  4. Isthmus

Answer: 2. Cuneus

Anatomy Of Cerebellum And 4th Ventricle Question And Answers

Cerebellum And Fourth Ventricle Question And Answers

Question 1. Write a note on the cerebellum.
Answer:

Cerebellum

It is the largest part of the hindbrain.

Cerebellum And Fourth Ventricle Anatomical Subdivisions Of Cerebellum

Cerebellum Dimensions, Location, And Extent

  • It weighs about 150 g
  • It is located in the posterior cranial fossa below tentorium cerebelli, posterior to pons and medulla
  • It is separated from the pons and medulla by the cavity of fourth ventricle
  • Its surface consists of numerous slit-like sulci called fissures and parallel folds in between them called folia
  • It consists of two hemispheres united by vermis
  • Each hemisphere is connected to three parts of the brainstem by three pairs of large fier tracts called cerebellar peduncles.

Cerebellum External Features

  • Cerebellum External Features Parts
    • It consists of two large hemispheres and a narrow median worm-like portion called the vermis
    • The superior and inferior aspect of vermis is termed as superior and inferior vermis, respectively.
  • Cerebellum External Features Surfaces
    • It consists of superior and inferior surfaces
    • The superior surface is convex and the two hemispheres are continuous with each other on this surface
    • The inferior surface has a deep median notch called vallecula which separates two cerebellar hemispheres.
  • Cerebellum External Features Notches
    • The anterior cerebellar notch is a wide shallow notch that is present on the anterior aspect and accommodates pons and medulla
    • The posterior cerebellar notch is a deep and narrow notch that lodges the falx cerebelli.
  • Cerebellum External Features Fissures: Consist of three well-marked fissures
  1. The horizontal fissure which marks the junction between the superior and inferior surfaces of the cerebellum. It runs along lateral and posterior margins of the cerebellum
  2. The posterolateral fissure separates the flcculonodular lobe from the rest of the cerebellum. It lies on the inferior surface of cerebellum
  3. The V shaped fissure prima divides cerebellum to anterior and posterior lobes and cuts the superior vermis at the junction of anterior two third and posterior one-third.

Cerebellum Subdivisions

  • Anatomical Subdivision: Anatomically the cerebellum is divided into
    • Anterior lobe
    • Posterior lobe
    • Flocculonodular lobe.
  • Morphological Division: Based on phylogenetic and functional criteria cerebellum is divided into
    • Archicerebellum
    • Paleocerebellum
    • Neocerebellum.

Cerebellum Functions: Basic functions include

  • Maintenance of equilibrium
  • Regulation of muscle tone
  • Coordination of somatic motor activities.

Cerebellum Internal Structure

  • It is made up of thin surface layer of grey matter called the cortex and the central core of the white matter.
  • Within the central core masses of grey matter are embedded and they are known as intracerebellar nuclei.
  • The intracerebellar nuclei includes the following:
    • The dentate nucleus
    • The emboliform nucleus
    • The globose nucleus
    • The fastigial nucleus.
  • The cerebellar cortex is folded so that the surface presents with series of transverse fissures and intervening narrow leaf-like bands called folia
  • The central core is arranged in the form of branching pattern of tree.

Cerebellum Blood Supply: Supplied by the following

  • Superior cerebellar artery which supplies the superior surface
  • Anterior inferior cerebellar artery which supplies the anterior part of the inferior surface
  • Posterior inferior cerebellar artery which supplies the posterior part of inferior surface.

Cerebellum Applied

  • The cerebellar lesions due to trauma, stroke tumors, etc. produce sign and symptoms which are collectively known as cerebellar syndrome.
  • It includes generalizes muscular hypotonia, intention tremors, adiadochokinesis, dysarthria, nystagmus, and generalized swaying.

Question 2. Write a note on cerebellar peduncles.
Answer:

Cerebellar peduncles

  • The efferent and afferent fibers of the cerebellum are grouped into large bundles of fibers and are known as cerebellar peduncles
  • These are three in number, superior, inferior, and middle cerebellar peduncles.

Superior Cerebellar Peduncle

  • The superior cerebellar peduncle connects the cerebellum to the midbrain
  • It emerges from anterior cerebellar notch and forms the lateral boundary of upper half of fourth ventricle
  • It consists only of effrent fiers from dentate nucleus to red nucleus, thalamus, and cerebral cortex of opposite side.

Middle Cerebellar Peduncle

  • It connects cerebellum to pons
  • It is the largest among the three
  • It is formed at the posterolateral margin of pons
  • It consists only of afferents from pontine nuclei of the opposite side.

Inferior Cerebellar Peduncle

  • It connects the cerebellum to medulla
  • It is formed at the posterolateral aspect of medulla
  • It consists of both affrents and effrent fiers
  • It consists of mainly afferents to the cerebellum from the spinal cord, olivary nucleus, reticular formation of medulla and vestibular nuclei, and nerve
  • It also contains few efferents from the cerebellum to the medulla, i.e. vestibular nuclei and reticular formation.

Question 3. Write a short note on the interpeduncular fossa.
Answer:

Interpeduncular fossa

Rhomboidal space bounded by crus cerebri of cerebrum laterally, anteriorly by optic chiasma, and posteriorly by pons.

Cerebellum And Fourth Ventricle Interpenuncular Fossa And Its Contents

Interpeduncular Fossa Contents

  • Two spherical bodies called mammillary bodies
  • Raised area of grey matter anterior to mammillary bodies called tuber cinereum
  • Infundibulum which connects the pituitary to tuber cinereum
  • Posterior perforated substance, a layer of grey matter present in the angle between crus cerebri
  • Oculomotor nerve.

Question 4. Write a note on floor of fourth ventricle.
Answer:

Floor of fourth ventricle

  • It is otherwise known as the rhomboid fossa
  • It is formed by the posterior surface of pons and upper part of the medulla
  • It is divided into three parts, the upper triangular part bounded by a superior cerebellar peduncle, the lower triangular part bounded by gracile and cuneate tubercles, and the inferior cerebellar peduncles.

Cerebellum And Fourth Ventricle Features Of The Floor Of Fourth Ventricle

Floor Of Fourth Ventricle Features

  • The floor is divided into symmetrical right and left halves by median sulcus which extends from the aqueduct of the midbrain above to the central canal below
  • The widest part is transversely crossed by striae medullaris, which are white fiers from arcuate nuclei
  • On the other side of the median sulcus, there is a longitudinal elevation called medial eminence and is bounded laterally by sulcus limitans
  • At a lateral angle, the region lateral to sulcus limitans overlies the vestibular nuclei and is known as vestibular area
  • The upper end of the sulcus limitans widens to form a triangular depression known as superior fovea. Above the superior fovea it flttens and present bluish grey area called locus coeruleus
  • The lower part of sulcus limitans presents a depression called inferior fovea
  • On either side of medial eminence at the level of superior fovea oval-shaped facial colliculus is present
  • The sulcus limitans divides the medial eminence into two triangles, the hypoglossal triangle above and the vagal triangle below
  • The hypoglossal triangle divided into medial and lateral parts by the nucleus of the hypoglossal nerve
  • The vagal triangle overlies nuclei of the vagus, glossopharyngeal, and cranial accessory nerve
  • The vagal triangle is crossed by a narrow ridge called funiculus separates and the area between the funiculus separates and gracile tubercle is known as area postrema
  • The inferolateral margins present two narrow ridge called taenia and both taeniae meet at an inferior angle to form a fold called obex.

Cerebellum And Fourth Ventricle Multiple Choice Question And Answers

Question 1. All of the following are intracerebellar nuclei except:

  1. Dentate nucleus
  2. Fastigial nucleus
  3. Globose nucleus
  4. Red nucleus

Answer: 4. Red nucleus

Question 2. The cerebellar lesion is characterized by all of the following:

  1. Ataxia
  2. Muscular hypotonia
  3. Nystagmus
  4. Tremors at rest

Answer: 4. Tremors at rest

Question 3. Th neocerebellum is concerned with:

  1. Maintenance of equilibrium
  2. Smooth performance of fie voluntary movements
  3. Regulating muscle tone and posture of trunk
  4. Regulating muscle tone and posture of limbs

Answer: 2. Smooth performance of fie voluntary movements

Cerebrospinal Fluid Question And Answers

Cerebrospinal Fluid Question And Answers

Question 1. Write a short note on cerebrospinal flid (CSF).
Answer:

Cerebrospinal flid (CSF)

It is a modified tissue fluid present in the ventricular system of the brain and subarachnoid space around the brain and spinal cord.

Cerebrospinal Flid Formation

  • Produced mainly by the choroid plexus of lateral ventricle and also by choroid plexus of third and fourth ventricle
  • It is produced about 200 mL/hour.

Cerebrospinal Flid Circulation

  • Cerebrospinal fluid passes from each lateral ventricle to the third ventricle through the interventricular foramen
  • From third ventricle, it passes to fourth ventricle through cerebral aqueduct and to the subarachnoid space through median and lateral apertures of the fourth ventricles.

Cerebrospinal Fluid Absorption: Absorbed through arachnoid villi and granulations and drained to cranial venous sinuses.

Cerebrospinal Fluid Functions

  • Cerebrospinal fluid decreases the sudden pressure on nervous tissue
  • Nourishes nerve tissue
  • Pineal gland secretions reach the pituitary via CSF.

Cerebrospinal Fluid Applied

  • Lumbar puncture: It is done by passing a needle in L3 and L4 interspace to obtain cerebrospinal fluid for diagnostic and therapeutic purposes.
  • Hydrocephalus: It is a condition caused by obstruction to the flow of the cerebrospinal fluid in the ventricular system of the brain in children.

Cerebrospinal Fluid Circulation Of Cerebrospinal Fluid

Cerebrospinal Fluid Multiple Choice Question And Answers

Question 1. The cerebrospinal fluid is formed mainly by:

  1. Choroid plexus within the lateral ventricles
  2. Choroid plexus within the third ventricle
  3. Choroid plexus within the fourth ventricle
  4. Ependyma of the ventricles

Answer: 1. Choroid plexus within the lateral ventricles

Question 2. The term tela choroidea refers to:

  1. Ependymal element of choroid plexus
  2. Pial element of choroid plexus
  3. Vascular tufts of choroid plexus
  4. None of the above

Answer: 2. Pial element of choroid plexus

 

 

Ventricles Of Brain Question And Answers

Ventricles Of Brain Question And Answers

Question 1. Write a note on the third ventricle.
Answer:

Third ventricle

  • It is the cavity of the diencephalon
  • It is a slit-like cavity present between two thalami and hypothalamus
  • It extends from the lamina terminalis anteriorly to superior end of the cerebral aqueduct posteriorly
  • Its cavity is lined by ependymal cells and traversed horizontally by inter thalamic adhesion (mass of gray matter) connecting two thalami.

Third Ventricle Boundaries

  • The third ventricle has anterior and posterior walls, roof and floor, and two lateral walls
  • The anterior wall is formed by the anterior column of the fornix, anterior commissure, and lamina terminalis
  • The posterior wall is formed by the pineal gland, posterior commissure, and commencement of cerebral aqueduct
  • Lateral wall is divided into upper and lower halves by the hypothalamic sulcus which extends from interventricular foramen to cerebral aqueduct
    • The upper part of the lateral wall is large and is formed by medial surface of the anterior 2/3rd of the thalamus
    • The smaller lower part of lateral wall is formed by the hypothalamus.
  • The roof is formed by ependyma extending between two thalami
  • The floor is formed by optic chiasma, tuber cinereum, mammillary bodies, posterior perforated substance, and tegmentum of brain.

Third Ventricle Communications

  • Anteriorly, the 3rd ventricle communicates with lateral ventricle on each side through the interventricular foramen of Monro
  • Posteriorly, it communicates with the 4th ventricle through the cerebral aqueduct of Sylvius.

Third Ventricle Recesses

  • The cavity extends to surrounding structures as pockets like protrusions called recesses.
  • The following recesses are associated with 3rd ventricle:
    • Infundibular recess: Tunnel shaped recess extending through tuber cinereum to infundibulum
    • Optic recess: Angular recess located at the junction of the anterior wall and floor of the ventricle
    • Anterior recess: Triangular recess located between diverging anterior columns of fornix and anterior commissure anteriorly and interventricular foramen posteriorly
    • Suprapineal recess: It is a blind diverticulum extending between stalk of the pineal gland and tela choroidea
    • Pineal recess: A small diverticulum extending between the superior and inferior lamellae of the stalk of pineal gland.

Ventricles Of Brain

Question 2. Write a note on the lateral ventricle.
Answer:

Lateral ventricle

  • Each lateral ventricle is a C-shaped cavity present in each cerebral hemisphere
  • It is lined by ependymal cells.

Lateral Ventricle Communications: Each ventricle communicates with 3rd ventricle through the interventricular foramen.

Lateral Ventricle Parts: Each ventricle consists of the following parts

  1. Central part
  2. Anterior horn
  3. Posterior horn
  4. Inferior horn

1. Central Part

  • It is located within the parietal lobe extending from the interventricular foramen to the splenium of the corpus callosum
  • It is triangular in cross-section and consists of a roof, floor, and a medial wall
  • The floor is formed by body of the caudate nucleus, stria terminalis, thalamostriate vein, and thalamus
  • The roof is formed by body of corpus callosum and the medial wall by septum pellucidum.

2. Anterior Horn

  • It is the anterior prolongation of the central part into the frontal lobe
  • It lies in between the interventricular foramen and genu of corpus callosum
  • It consists of a roof, floor, anterior, medial, and lateral walls
    • Roof: Formed by the body of corpus callosum
    • Floor: Formed by rostrum of corpus callosum
    • Anterior wall by genu of corpus callosum
    • Medial wall by septum pellucidum
    • Lateral wall by head of caudate nucleus.

3. Posterior Horn

  • It is the posterior prolongation of the central part into occipital lobe
  • It consists of a roof, floor, medial and lateral wall
  • Roof, floor and lateral wall are formed by the tapetum of the corpus callosum
  • The medial wall is formed by forceps major of the corpus callosum and calcarine sulcus.

4. Inferior Horn

  • It is the largest horn
  • It appears as a slit and consists of a roof and floor
  • The roof is formed by the tapetum of the corpus callosum, stria terminalis, and tail of the caudate nucleus
  • The floor is formed by the hippocampus and collateral eminence.

Ventricles Of Brain Multiple Choice Question And Answers

Question 1. Regarding the cavities of the brain, all of the following statements are correct except:

  1. Right and left lateral ventricles are cavities within the right and left cerebral hemispheres respectively
  2. Third ventricle is a cavity within the diencephalon
  3. The cerebral aqueduct is the cavity within the pons
  4. The fourth ventricle is the cavity within the hindbrain

Answer: 3. Cerebral aqueduct is the cavity within the pons

Question 2. An infant with hydrocephalus was diagnosed to have a blocked outlet passage from the third ventricle. The blocked passage is:

  1. Central canal of medulla
  2. Foramen of Monro
  3. Aqueduct of Sylvius
  4. Foramen of Magendie

Answer: 3. Aqueduct of Sylvius

Blood Supply Of Brain And Spinal Cord Question And Answers

Blood Supply Of Brain And Spinal Cord Question And Answers

Question 1. Write a short note on the circle of Willis.
Answer:

Circle of Willis

Blood Supply Of Brain And Spinal Cord Circle Of Willis And Intracranial Branches Of Internal Cartid And Vertebasilar Arteries

Abbreviation: ICA = Internal carotid artery

At the base of the brain around interpeduncular fossa the branches of basilar artery and internal carotid artery (ICA) anastomose form a six-sided polygon known as the circle of Willis or Circulus arteriosus.

Willis Formation

  • Anteriorly by the anterior communicating artery and anterior cerebral artery
  • Posteriorly by the basilar artery dividing into two posterior cerebral arteries
  • Laterally by posterior communicating artery connecting the internal carotid artery with the posterior cerebral artery.

Willis Functional Significance

  • Normally, there is no mixing of blood of two vertebral arteries in basilar artery, two anterior cerebral arteries in anterior communicating artery, and internal carotid and posterior cerebral arteries in posterior communicating arteries
  • As a result, the right half of brain is supplied by right vertebral and right internal carotid arteries, and left half of brain is supplied by left vertebral and left internal carotid arteries
  • In case of blockade of any major arteries, the collateral circulation will be provided and thus act as an arterial traff circle.

Willis Applied

Berry aneurysms: These are congenital aneurysms due to the deficiency of tunica media layer of the arterial wall.

Question 2. Write a short note on blood supply of spinal cord.
Answer:

Blood supply of spinal cord

Blood Supply Of Brain And Spinal Cord Sources Of Arterial Supply To The Spinal Cord

Blood Supply Of Brain And Spinal Cord Intrinsic Arterial Supply Of Spinal Cord

The blood supply of the spinal cord can be studied under two headings:

  1. Arterial supply
  2. Venous drainage.

1. Arterial Supply: The spinal cord is mainly supplied by the following arteries

  • Anterior spinal arteries
  • Posterior spinal arteries
  • Segmental arteries.

Anterior Spinal Arteries

  • Formed by the union of spinal branches of vertebral artery
  • It runs along the anterior median fissure and terminates along fium terminale.

Posterior Spinal Arteries

  • There are two posterior spinal arteries arising from vertebral arteries or posterior inferior cerebellar artery
  • Each artery runs along the posterolateral sulcus and divides into two collaterals along medial and lateral side of the posterior nerve roots
  • These arteries are reinforced by segmental arteries which communicate around cord to form plexus called vasocorona and supply superficial regions of the cord.

Segmental Arteries

  • These are spinal branches of deep cervical, ascending cervical, posterior intercostal, lumbar, and lateral sacral arteries
  • They reach the spinal cord, as the anterior and posterior radicular arteries.

2. Venous Drainage: The veins form six longitudinal venous channels which are as below

  • Two median longitudinal veins: one in anterior median sulcus and other in the posterior median sulcus
  • Two anterolateral veins: one on either side posterior to anterior nerve roots
  • Two posterolateral veins: one on either side posterior to posterior nerve roots.

Spinal Cord Applied: Anterior spinal artery syndrome occurs due to occlusion of the anterior spinal artery.

Question 3. Write a note on the blood supply of brain.
Answer:

Blood supply of brain

The blood supply of the brain can be divided into:

  1. Arterial supply
  2. Venous drainage.

1. Arterial Supply: The arterial supply of the brain can be studied under the arterial supply of cerebral surfaces and arterial supply of other parts of the brain.

  • Arterial Supply of Cerebral Surfaces
    • Superolateral Surface: It is mainly supplied by the following arteries
      • Middle cerebral artery: About two-thirds of the superolateral surface is supplied. It supplies the primary sensory and motor area, frontal eye field, Broca and Wernicke’s area
      • Anterior cerebral artery: It supplies the narrow strip of cortex adjoining the superomedial border up to the parieto-occipital sulcus
      • Posterior cerebral artery: It supplies a narrow strip of cerebral cortex along with temporal lobe and occipital lobe.
    • Medial Surface: It is mainly supplied by the following arteries
      • Anterior cerebral artery: ThE anterior 2/3rd of the medial surface is supplied by the anterior cerebral artery. It includes mainly the paracentral lobule
      • Middle cerebral artery: It supplies the temporal pole of the temporal lobe
      • Posterior cerebral artery: It supplies the occipital lobe including the visual cortex.
    • Inferior Surface: It is mainly supplied by the following arteries
      • Posterior cerebral artery: It supplies almost the entire inferior surface except for the temporal pole
      • Middle cerebral artery: It supplies the lateral part of the orbital surface of frontal lobe and temporal pole of temporal lobe
      • Anterior cerebral artery: It supplies the medial part of orbital part of frontal lobe.
  • Arterial Supply of Other Parts of Brain: The arterial supply of other parts of the brain includes the following
    • The corpus striatum and internal capsule: By central branches of the middle cerebral artery and anterior cerebral artery
    • Thalamus: By central branches of posterior communicating, posterior cerebral and basilar arteries
    • Midbrain: By posterior cerebral, superior cerebellar and basilar arteries
    • Pons: By basilar, superior cerebellar and anterior inferior cerebellar arteries
    • Medulla oblongata: By vertebral, anterior spinal, posterior spinal, posterior inferior cerebellar and basilar arteries
    • Cerebellum: By superior, anterior inferior and posterior inferior cerebellar arteries.

Blood Supply Of Brain And Spinal Cord Arterial Supply Of Supermedical Surface Of Left Cerebalhemisphere

Blood Supply Of Brain And Spinal Cord Arterial Supply Of Inferior Surface Of Left Cerebral Hemisphere

2. Venous Drainage of Brain: The venous drainage of brain can be studied under the following headings

  • Venous Drainage of Cerebral Surfaces: The venous drainage of the cerebral surfaces are as follows:
    • Superolateral Surface: The superolateral surface is drained by the following veins
      • Superior cerebral veins which drain the upper part of hemisphere into the superior sagittal sinus
      • Inferior cerebral veins drain the lower part of the cortex into superficial middle cerebral vein and into the transverse sinus.
    • Medial Surface: Medial surface is drained by the following veins
      • Superior cerebral veins drain the upper part into superior sagittal sinus
      • Inferior cerebral veins drain the lower part into the inferior sagittal sinus
      • Anterior cerebral vein drains the anterior part.
    • Inferior Surface
      • The inferior surface is drained by the following veins:
      • Inferior cerebral veins from the orbital part drain into superficial, middle cerebral, and anterior cerebral veins
      • Inferior cerebral veins from the tentorial part drain into venous sinuses at base of skull and superficial middle cerebral vein which ultimately drains to straight sinus.
  • Venous Drainage of Other Parts of the Brain
    • The corpus striatum and internal capsule are drained by two sets of striate veins and ultimately drains into basal vein
    • The thalamus is drained by the internal cerebral vein into the cavernous sinus
    • The midbrain is drained by veins into the great cerebral or basal vein
    • The pons and medulla drain into superior and inferior petrosal sinuses, transverse and occipital sinuses
    • The cerebellum is drained into the straight, transverse, and superior petrosal sinus.

Blood Supply Of Brain Applied: Subdural hemorrhage occurs due to rupture of cerebral veins in subdural space.

Blood Supply Of Brain And Spinal Cord Multiple Choice Question And Answers

Question 1. All of the following arteries take part in the formation of a circle of Willis except:

  1. Anterior communicating
  2. Anterior cerebral artery
  3. Middle cerebral artery
  4. Posterior cerebral artery

Answer: 3. Middle cerebral artery

Question 2. All of the following arteries arise from the basilar artery except:

  1. Posterior cerebral
  2. Posterior inferior cerebellar
  3. Superior cerebellar
  4. Anterior inferior cerebellar

Answer: 2. Posterior inferior cerebellar

Question 3. Anterior choroid artery is a branch of:

  1. Anterior cerebral artery
  2. Middle cerebral artery
  3. Internal carotid artery
  4. Posterior cerebral artery

Answer: 3. Internal carotid artery

Cranial Nerves Question And Answers

Cranial Nerves Introduction

  • There are twelve pairs of cranial nerves designated by Roman numerals.
  • The first two pairs are attached to the forebrain and the next 10 are attached to the brainstem, i.e. 3 and 4 to the midbrain; 5, 6, 7, and 8 to the pons and the 9, 10, 11, and 12 to the medulla.
  • They are numbered from 1 to 12 in a craniocaudal sequence of their attachment.
  • During development, the middle mantle layer of neural tube which represents the gray matter differentiated into dorsal alar lamina (sensory) and ventral basal lamina (motor) which are separated by the sulcus limitans.
  • In the brainstem, the alar and basal lamina lie in same ventral plane, and the gray matter forms separate longitudinal functional columns. The columns from basal lamina (motor columns) are medial and from alar lamina (sensory) are lateral in position.
  • In spinal cord, the gray matter is differentiated into four functional columns, i.e. two somatic and two visceral functional columns.
  • The somatic columns are general somatic efferent (motor or anterior horn) and general somatic afferent (sensory or posterior horn) and they supply the structures derived from somites.
  • The visceral columns are general visceral afferent (sensory) and general visceral efferent (motor) and supply the viscera, vessels, and glands.
  • In addition to the four functional columns, there are three more columns namely special visceral efferent (motor) and special visceral afferent (sensory) for the branchial apparatus of the head region and special somatic afferent (for the special senses).
  • Thus a total of seven columns (3 motor and 4 sensory) are formed and each column in turn breaks up into smaller fragments to form nuclei of the cranial nerves.
  • A cranial nerve consists of motor fibers (motor nerve) or sensory fibers (sensory nerve) or both motor and sensory fibers (mixed nerve).
  • The motor fibers arise as outgrowths of axons from motor nuclei situated within the central nervous system (CNS) whereas sensory fibers arise as outgrowths of axons from cells situated within sensory ganglia and terminate in sensory nuclei.

Cranial Nerves Inferior Surface Of Brain Showinmg The Cerebrum, Cerebellum And Brainstem

  • The motor fibers of cranial nerve can be of the following types:
    • General somatic efferent (GSE) fiers which supply striated muscles developed from somites.
    • Special visceral efferent (SVE) fiers which supply muscles developed from mesoderm.
    • General visceral efferent (GVE) fibers which are preganglionic parasympathetic fibers and supply glands, smooth muscles of viscera, and blood vessels.
  • The sensory fibers of cranial nerve can be of the following types:
    • General somatic afferent (GSA) fiers carry general sensations of pain, touch, and temperature and proprioceptive sensations of vibration, position, and joint sense.
    • General visceral afferent (GVA) fiers which carry sensations of distention and ischemic pain from viscera.
    • Special visceral afferent (SVA) fiers which carry special sensation of taste from tongue.
    • Special somatic afferent (SSA) which carry special sensations of smell, hearing, and balance.

Cranial Nerves Course And Branches

Cranial Nerves Question And Answers

Question 1. Write a note on the olfactory nerve.
Answer:

Olfactory nerve.

  • It is the 1 cranial nerve
  • It is purely sensory and carries smell from nasal cavity.

Cranial Nerves Olfactory Nerve

Cranial Nerves Components Of Olfactory Path

Olfactory Nerve Functional Components: Special somatic afferent fibers carry the special sensation of smell from the olfactory region of nasal cavity to the olfactory bulb.

Olfactory Nerve Course And Relations

  • It consists of minute bundles of non-myelinated nerve fibers which arise from the olfactory epithelium of nasal cavity
  • Then it passes through the cribriform plate and enters anterior cranial fossa and terminates in the olfactory bulb
  • In the olfactory bulb, they synapse with mitral cells
  • The neurons from the olfactory bulb form olfactory tract and widens at olfactory trigone at anterior perforated substance
  • These neurons are in the form of striae terminate in the paraterminal gyrus and primary olfactory cortex.

Cranial Nerves Course And Pathway Of Olfactory Nerve

Olfactory Nerve Clinical Testing: The olfactory nerve is tested by asking the patient to smell common odors like clove, and peppermint from each side of nose separately with eyes closed.

Olfactory Nerve Applied

  • Anosmia refers to the inability to perceive the smell
  • Allergic rhinitis can cause temporary olfactory impairment
  • In severe head injuries involving the anterior cranial fossa, the olfactory bulb may be separated from olfactory nerves or the nerves may be injured, producing anosmia and cerebrospinal fluid (CSF) leakage.

Question 2. Write a note on optic nerve.
Answer:

Optic nerve

  • It is the 2 cranial nerve
  • It is purely sensory and is responsible for vision.

Cranial Nerves Optic Nerve

Cranial Nerves Origin Of Optic Nerve From The Retina And Trermination In Optic Chiasma

Cranial Nerves Components Of Visual Pathway

Optic Nerve Functional Components: Special somatic afferent fiers carry sense of sight from the visual field of corresponding eye.

Optic Nerve Course And Relations

  • The fibers of optic nerve arise from ganglion cells of retina and converge towards the optic disc and pierce retina, choroid, and sclera to leave the eyeball
  • After emerging from eyeball, fiers unite to form optic nerve which pass through the orbit and enter into middle cranial fossa where both optic nerves of two sides unite to form optic chiasma
  • From the optic chiasma, fibers diverge and are known as optic tracts which relay in lateral geniculate body
  • They run in retrolenticular part of internal capsule and form optic radiations and terminate in and around calcarine sulcus of occipital lobe (visual cortex).

Cranial Nerves Course And Pathway Of Optic Nerve Flowchart

Optic Nerve Visual Pathway

Cranial Nerves Visual Pathway

Optic Nerve Parts: Divided into

  1. Intraorbital part
  2. Canalicular part
  3. Intracranial part.

Optic Nerve Clinical Testing

  • The nerve is tested by performing tests for:
  • Visual acuity of near and distant vision
  • Visual field either manually by confrontation method or perimetry
  • Color vision by using ishihara charts
  • Light reflexes.

Optic Nerve Applied

  • Lesions of the optic pathway may have many pathological causes. Expanding tumors of the brain and the meninges and cerebrovascular accidents are commonly responsible.
  • Lesions of the optic nerve may be at different levels with different affects, as follows:
    • Complete lesion of the optic nerve of one side leads to complete blindness in the corresponding eye
    • Compression of optic chiasma causes bitemporal hemianopia because the nasal fibers from both sides are interrupted
    • Lesion of the optic tract and optic radiation of one side each leads to corresponding nasal and contralateral temporal hemianopia
    • Circumferential blindness is caused most commonly by optic neuritis.

Question 3. Write a note on oculomotor nerve, trochlear, and abducens nerve.
Answer:

Oculomotor nerve, trochlear, and abducens nerve

Cranial Nerves Nuclei Origin, Intraneural Course In Midbrain And Points Of Emergence From Crus Cerevbri Of The Oculomotor Nerve

Cranial Nerves Distribution Of Oculometer Nerve Inside The Orbit

Oculomotor Nerve

  • It is the 3 cranial nerve
  • It is purely motor and supplies most of the muscles of eye and plays major role in accommodation.

Cranial Nerves Oculomoror Nerve

Oculomotor Nerve Functional Components

  • GSE fibers supply all extraocular muscles except lateral rectus and superior oblique and they arise from a somatic component of oculomotor nucleus
  • GVE fibers arise from the parasympathetic component of the Edinger-Westphal nucleus and supply sphincter pupillae and ciliary muscle.

Oculomotor Nerve Course And Relations

  • It arises from oculomotor sulcus on medial aspect of cerebral peduncle
  • It runs forward and laterally between posterior cerebral and superior cerebellar artery and pass through tentorium cerebelli and reach middle cerebral fossa
  • It then pierces dura mater in oculomotor triangle and enter lateral wall of cavernous sinus and lie superior to trochlear, ophthalmic and maxillary nerve
  • It then divides into upper and lower divisions
  • These two divisions enter into orbit and smaller upper division passes above optic nerve and passes through superior rectus and supply it and then supply levator palpebrae superioris
  • The lower division passes below optic nerve and gives three branches which supplies the medial rectus, inferior rectus, and inferior oblique.

Cranial Nerves Course And Pathway Of Oculomotor Nerve

Oculomotor Nerve Applied: Oculomotor nerve may undergo complete or incomplete lesions.

  • Complete lesions of oculomotor nerve leads to:
    • Ptosis: Drooping of the upper eyelid due to paralysis of levator palpebrae
    • External strabismus due to paralysis of medial rectus and consequent unopposed action of lateral rectus
    • Pupillary dilatation due to paralysis of sphincter pupillae
    • Loss of accommodation and of light reflx is due to paralysis of sphincter pupillae and ciliary
    • Diplopia: The false image being the higher.
  • Incomplete lesions of oculomotor nerve are common and may spare the extraocular or intraocular muscles.
    • The condition in which the innervation of extraocular muscles is spared with selective loss of autonomic innervation is called internal ophthalmoplegia.
    • The condition in which the intraocular muscles are spared with paralysis of extraocular muscles is called external ophthalmoplegia.

Trochlear Nerve

  • It is the 4 cranial nerve
  • It is purely motor and supply only superior oblique of eyeball.

Cranial Nerves Nucleus Of Origin, Intraneural Course And Point Of Emergence Of Trochlear Nerve From The Miodbrain

Cranial Nerves Structures Passing Through Optic Canal And Superior Orbital Fissure And Muscles Taking Origin From Common Tendinous Ring At The Apex Of Orbit

Trochlear Nerve Functional Components: General somatic efferent fibers arise from trochlear nucleus in midbrain and supply superior oblique muscle.

Cranial Nerves Trochlear Nerve

Trochlear Nerve Course And Relations

  • It arise from the dorsal aspect of the midbrain, one on the either side of frenulum veli, and wounds around superior cerebral and superior cerebellar peduncle
  • It then passes between posterior cerebral and superior cerebellar arteries and lies below free margins of tentorium cerebelli
  • It then enters into cavernous sinus by piercing roof and runs forwards in the lateral wall and cross the oculomotor nerve
  • It then enters the orbit through superior orbital fissure and runs medially above levator palpebrae superioris and supply superior oblique muscle.

Cranial Nerves Course And Pathway Of Trochlear Nerve Flowchart

Trochlear Nerve Applied

  • The conditions most commonly affecting the trochlear nerve include stretching or bruising as a complication of head injuries, cavernous sinus thrombosis, and aneurysm of the internal carotid artery (ICA).
  • As a result of such injuries, interruption of the trochlear nerve paralysis the superior oblique, limiting inferolateral ocular movement; the affected eye rotates medially, producing Diplopia.
  • There is also some degree of extorsion, because the superior oblique which normally produces intorsion, is not available.
  • To compensate for this, the patient characteristically tilts the head towards the opposite shoulder.

Abducens Nerve

  • It is the 6 cranial nerve
  • It is purely motor and supplies only the lateral rectus muscle and it is called so because it abducts the eyeball.

Cranial Nerves Abducents Nerve

Abducens Nerve Functional Components

  • General somatic efferent fibers arise from abducens nucleus in pons and supply lateral rectus
  • General somatic afferent fibers carry proprioceptive sensations from lateral rectus and terminate in mesencephalic nucleus of the trigeminal nerve.

Abducens Nerve Course And Relations

  • It arises from the lower border of pons opposite to the pyramid of medulla and runs upwards and close to anterior cerebellar artery and pierces the dura mater
  • It then passes through the medial wall of inferior petrosal sinus and arches forward directly over the sharp ridge of petrous temporal bone and enter into the firo-osseous canal
  • It then enters the cavernous sinus by piercing the posterior wall and runs inferolaterally to ICA.
  • It then enters into orbit through superior orbital fissure and runs forward to lateral side and supply lateral rectus muscle.

Cranial Nerves Course And Pathway Of Abducens Nerve Flowchart

Abducens Nerve Applied

  • In lesions of the abducens nerve, the patient cannot turn the eye laterally. When the patient is looking ahead, the lateral rectus is paralyzed and the unopposed medial rectus pulls the eyeball medially, causing internal strabismus. There is diplopia.
  • The long course of the nerve through the cisterna pontis and its sharp bend over the petrous temporal bone make the nerve liable to damage in conditions producing raised intracranial pressure.
  • However, the most common causes of lesions include damage due to head injuries, cavernous sinus thrombosis or aneurysm of the ICA.

Abducens Nerve Clinical Testing

  • The clinical testing of the third, fourth, and sixth nerves are usually done together. These include:
  • On inspection look for ptosis, lid retraction, and squint
  • Testing for movements of extraocular muscles, ask for diplopia, and look for nystagmus
  • Eliciting direct and consensual reflex.

Question 4. Write a note on trigeminal nerve.
Answer:

Trigeminal nerve

  • It is the V cranial nerve
  • It is the largest cranial nerve
  • It is a mixed nerve carrying both sensory and motor fibers but predominantly it is sensory.

Cranial Nerves Points Of Emergence Of Motor And Sensory Roots Of Trigeminal Nerve From The Pons And Emergence Of Divisions

Cranial Nerves Termination Of Sensory Fibers Of Ophthalmic, Maxillary And Mandibular Nerves

Cranial Nerves Trigeminal Nerve

Trigeminal Nerve Functional Components

  • General somatic affrent (GSA) fiers carry
  • Exteroceptive sensations (pain, touch, and temperature) from skin of head and face, mucous membrane of mouth, nasal cavity, meninges, etc., and terminate in main sensory nucleus and spinal nucleus of trigeminal nerve
  • Proprioceptive sensations from muscles of mastication, temporomandibular joint, and teeth and terminate in the mesencephalic nucleus of trigeminal nerve and reticular formation of brainstem.
  • Special visceral efferent (SVE) fiers arise from the motor nucleus of trigeminal nerve and supply muscles derived from the 1st pharyngeal arch, viz muscles of mastication, mylohyoid, anterior belly of digastric, tensor palati and tensor tympani.

Cranial Nerves Nuclei Of Origin And Branches Of Facial Nerve Along Its Long Course

Trigeminal Nerve Nuclei

  • Spinal nucleus of 5th nerve: It takes pain and temperature sensations from the most of the face area which relay here.
  • Superior sensory nucleus of 5th nerve: Th fiers carrying touch and pressure relay here.
  • Mesencephalic nucleus: It receives proprioceptive impulses from muscles of mastication, temporomandibular joint.
  • Motor nucleus of 5th nerve: The fibers from the nucleus supply eight muscles derived from 1st branchial arch.

Trigeminal Nerve Course And Relations

  • The nerve arises by two roots, a small medial motor root and a large lateral sensory root from the ventrolateral aspect of pons at its junction with the middle cerebellar peduncle.
  • The sensory root passes forwards and laterally over the apex of petrous temporal bone to enter the middle cranial fossa.
  • Here the nerve presents a dilatation called the trigeminal ganglion and it occupies the dural cave known as the Meckel’s cave.

The convex surface of the ganglion gives of three divisions:

1. Ophthalmic nerve: It arises from the anterolateral aspect of the ganglion and enters the lateral wall of cavernous sinus and lies below the trochlear nerve.

  • In the cavernous sinus it divides into three branches nasociliary nerve, lacrimal nerve, and frontal nerve.
  • All these enter the orbit through superior orbital fissure.

Cranial Nerves Course And Pathway Of Opthalmic Nerve Flowchart

2. Maxillary nerve: It arises from the ganglion and enters the lateral wall of cavernous sinus it occupies the lowest position and leaves the sinus to enter the pterygopalatine fossa through foramen rotundum.

Cranial Nerves Course And Pathway Of Maxillary Nerve Flowchart

3. Mandibular nerve: After arising from the ganglion it immediately enter the infratemporal fossa through foramen ovale.

Cranial Nerves Course And Pathway Of Mandibular Nerve Flowchart

  • The motor root passes forwards and laterally deep to the sensory root and enters the infratemporal fossa through foramen ovale and after passing through the foramen ovale it joins the mandibular nerve.

Trigeminal Nerve Distribution

Cranial Nerves Summary Of Distribution Of Three Divisions Of The Maxillary Nerve

Trigeminal Nerve Clinical Testing

  • The motor part is tested by testing the temporalis, a masseter, and pterygoids
  • The masseter and temporalis is palpated after clenching the teeth
  • Opening the mouth against resistance is used to test the pterygoid
  • The sensory part is tested by testing the seven areas on each side of the face away (from midline) for pain, touch, and temperature.
  • The corneal reflex, conjunctival reflex, and jaw jerk is also elicited.

Trigeminal Nerve Applied

  • Lesion of the whole trigeminal nerve causes anesthesia of the anterior half of the scalp, of the face (except a small area near the angle of mandible), of the cornea and conjunctiva, the mucosa of the nose, mouth, and presulcal part of the tongue. Paralysis and atrophy occur in the muscles supplied by the nerve also.
  • Trigeminal Neuralgia characterized by pain in the distribution of branches of the trigeminal nerve, is the most common condition affecting the sensory part of the nerve.
  • With the maxillary nerve affected, the pain is usually felt deeply in the face and nose between the mouth and orbit. The cause of maxillary neuralgia is often neoplasms and empyema of the maxillary sinus.
  • With the mandibular nerve affected, the pain is usually felt from mouth up to the ear and the temporal region.
  • The most common cause is a carious mandibular tooth or an ulcer and carcinoma of tongue.
  • With the ophthalmic nerve affected, the pain is usually felt in supraorbital region and is often associated with glaucoma or with frontal or ethmoidal sinusitis.

Question 5. Write a short note on facial nerve.
Answer:

Facial nerve

  • It is the 7 cranial nerve.
  • It is a mixed nerve but is predominantly a motor nerve.

Cranial Nerves Facial Nerve

Facial Nerve Functional Components

  • General somatic afferent (GSA) fiers carry general sensations from the skin of the auricle and terminate in the spinal nucleus of trigeminal nerve
  • General visceral efferent (GVE) fibers arise from lacrimatory and superior salivatory nuclei and supply secretomotor fibers to lacrimal, submandibular, and sublingual glands
  • Special visceral afferent (SVA) fibers carry special sensations of taste from anterior 2/3rd of the tongue except vallate papillae and terminate in the nucleus of tractus solitarius
  • Special visceral efferent (SVE) fibers arise from the motor nucleus of facial nerve and supply the muscles of facial expression.

Facial Nerve Nuclei: The fibers are connected to four nuclei situated in the lower pons.

  1. Motor nucleus (branchiomotor)
  2. Superior salivatory nucleus (parasympathetic)
  3. Lacrimatory nucleus (parasympathetic)
  4. Nucleus of tractus solitarius (gustatory).

Facial Nerve Course And Relations

  • The nerve consists of two distinct roots, a large medial motor root (facial nerve proper) and a small lateral sensory root (the nervus intermedius)
  • Both roots arise from the pontomedullary junction lateral to the superior end of the olive of medulla
  • The sensory root lies in between the motor root medially and vestibulocochlear nerve laterally
  • After emerging from the brainstem both the roots pass laterally and forwards in the cerebellopontine angle along with the vestibulocochlear nerve and labyrinthine artery
  • These structures then enter the internal acoustic meatus
  • In the meatus, the motor root is lodged in a groove on the vestibulocochlear nerve and the sensory root remains separate
  • At the lateral end of the internal acoustic meatus the two roots unite to form the trunk of the facial nerve and enter the facial canal in the petrous temporal bone
  • The course in facial canal can be divided into three parts by two bends
  • The first part is directed laterally above the vestibule, the second part runs backwards in relation to the medial wall of the middle ear above the promontory, and the third part is directed vertically downwards behind the promontory
  • The first bend at the junction of the first and second part is sharp and it lies over the anterosuperior part of the promontory and is also called the genu and possesses geniculate ganglion
  • The second bend is gradual and lies between the promontory and the aditus to the mastoid antrum
  • The facial nerve leaves the cranial cavity through stylomastoid foramen
  • After coming out through the stylomastoid foramen the facial nerve crosses the lateral side of the base of the styloid process
  • It then enters the posteromedial surface of the parotid gland and runs forward through the gland crossing the retromandibular vein and the external carotid artery
  • Behind the neck of the mandible, it divides into its fie terminal branches which emerge along the anterior border of the parotid gland.

Cranial Nerves Course And Pathway Of Facial Nerve Flowchart

Facial Nerve Branches And Distribution

  • Within the facial canal:
    • Greater petrosal nerve:
      • It arises from the geniculate ganglion and consist of the preganglionic parasympathetic fibers which relay in pterygopalatine ganglion
      • It then supplies the secretomotor fibers to lacrimal gland and mucous glands of nasal cavity and palate.
    • The nerve to stapedius
      • It arises from the vertical part of the facial nerve opposite to the pyramidal eminence and runs through a short canal to reach the stapedius to supply it
      • The muscle damps the excessive vibration of the stapes caused by high-pitched sounds. Paralysis of this muscle causes even the normal sounds to appear too loud.
    • The chorda tympani nerve
      • It arises from the vertical part of the facial nerve and enters the middle ear though the posterior canaliculus and then runs in close relation to the tympanic membrane and then passes between the long process of incus and handle of malleus and leaves the middle ear by entering the anterior canaliculus
      • It then traverses through the bony canaliculus and enters the infratemporal fossa through medial end of the petrotympanic fissure
      • It then passes medial to the spine of the sphenoid and enters the infratemporal fossa
      • In the infratemporal fossa, it joins the lingual nerve and carries:
        • Preganglionic secretomotor fibers to the submandibular ganglion to supply the submandibular and sublingual glands
        • Taste fibers from the anterior 2/3rd of the tongue except the circumvallate papillae.
  • At its exit from the stylomastoid foramen
    • Posterior auricular nerve
      • Arises just below the stylomastoid foramen
      • It supplies the auricularis posterior, occipital belly of occipitofrontalis, and intrinsic muscles on the back of auricle.
    • Nerve to posterior belly of digastric: It is a short branch and supplies the posterior belly of digastric muscle.
    • Nerve to stylohyoid: Arises with the stylohyoid muscle and supplies the stylohyoid muscle.
  • Communicating branches with adjacent cranial and spinal nerves
  • Six terminal branches that supply the muscles of facial expression include:
    1. Temporal
    2. Zygomatic
    3. Buccal
    4. Marginal
    5. Mandibular
    6. Cervical.

Facial Nerve Clinical Testing: Th testing of the facial nerve is done by carrying out the following:

  • Check for wrinkling of the forehead by asking the patient to look upwards. On the affected side the wrinkling will be reduced in the LMN type of facial paralysis
  • Forced eye closure is tested by asking the patient to tightly close the eyelid and the examiner tries to open the eyes with figers. Normally examiner is unable to overcome the closure but in case of LMN facial palsy the eye closure will be defective
  • On asking the patient to show the teeth, the angle of mouth will deviate to the opposite side of the lesion
  • Th examiner asks the patient to blow the cheeks and the symmetry on both sides is looked for and tries to expel the air by pressing on either side of the cheeks
  • Ask for hyperacusis or subjective assessment is done
  • Taste sensation in the anterior 2/3rd of the tongue is tested by using solutions of sugar or salt.

Facial Nerve Applied

  • The facial nerve may be injured or become dysfunctional anywhere along its course from the brainstem to the face. The paralysis may be supranuclear or intranuclear
  • Supranuclear facial paralysis, involving upper motor neurons pathway is usually a part of hemiplegia. It involves paralysis of the lower part of the face but not the upper (forehead and orbicularis oculi) because the facial nerve nucleus innervating the upper part of face receives fiers from cerebral cortex of both sides whereas the lower part innervating the lower part of the face receives contralateral fiers.
  • However, emotional movements of the lower face, as in smiling and laughing, are still possible (presumably there is an alternative pathway from the cerebrum)
  • Infranuclear lesions vary in its effects depending on the site of lesion. Due to the anatomical location of facial nerve, neighboring structures are inevitably involved
  • If the facial nucleus or facial pontine fibers are involved, there may be damage to the abducens nucleus (paralysis of lateral rectus), motor trigeminal nucleus may be involved (paralysis of masticatory muscles) and principal sensory nucleus and spinal trigeminal nucleus may also be involved (sensory loss of face)
  • Lesions in the posterior cranial fossa or internal acoustic meatus may involve the vestibulocochlear nerve, resulting in loss of taste from anterior part of tongue with ipsilateral deafness and facial paralysis
  • Lesions of facial nerve in the facial canal may involve nerve to stapedius causing excessive sensitivity to sound in one ear (hyperacusis)
  • When damage is in the petrous temporal bone, chorda tympani nerve is usually involved resulting in loss of taste from anterior two-thirds of the tongue
  • Bell’s Palsy: It is caused due to inflammation of facial nerve near the stylomastoid foramen or compression of its fiers near facial canal or stylomastoid foramen.
  • If the lesion is complete, the facial muscles are all equally affected, with the following complications:
    • There is facial asymmetry and the affected side is immobile.
    • The eyebrows are drooped, wrinkles are smoothed out and the palpebral fissure is widened by the unopposed action of levator palpebrae.
    • The lips remain in contact and cannot be pursued; in attempting to smile the angle of the mouth is not drawn up on the affected side, the lips remaining nearly closed.
    • Food accumulates in the cheek, from paralysis of buccinator and dribbles, or is pushed out between the paralyzed lips.
    • Platysma and the auricular muscles are paralyzed.
    • Tears will fly over the lower eyelid and saliva will dribble from the corner of the mouth.

Question 6. Write a note on the vestibulocochlear nerve.
Answer:

Vestibulocochlear nerve

  • It is the 8 cranial nerve.
  • It consists of two parts:
  1. Vestibular part called the vestibular nerve
  2. Cochlear part called the cochlear nerve.
  • The vestibular nerve is concerned with the maintenance of equilibrium while the cochlear nerve is concerned with hearing.

Cranial Nerves Vestibulocochlear Nerve

Vestibulocochlear Nerve Functional Components

  • Special somatic afferent (SSA) fibers carry sensory information necessary for maintenance of equilibrium and hearing from the membranous labyrinth of the internal ear
  • The fibers carrying sensory information for equilibrium terminate in the vestibular nuclei
  • The fibers carrying sensory information for hearing terminate in the dorsal and ventral cochlear nuclei.

Cranial Nerves Distribution Of Vestibular Nerve To Receptors In Semicircular Ducts, Utricle And Saccule And Of Cochlear Nerve To Organ Of Corti Inside Duct

Cranial Nerves Afferent And Efferent Connections Of Verstibular Nuclei

Cranial Nerves Cochlear Nerve And Auditory Pathway

Vestibulocochlear Nerve Nuclei

  • The vestibular nuclei occupy the vestibular area in the lateral part of floor of fourth ventricle
  • It consists of superior, inferior, lateral, and medial subdivisions
  • The nucleus receives the vestibular nerve, cerebellovestibular fiers from floccus and nodule, spinovestibular fibers, and reticulovestibular fibers
  • The connections of nuclei include the following:
    • Fibers to the archicerebellum through inferior cerebellar peduncle (vestibulocerebellar tract)
    • Fibers to motor nuclei of the brainstem (3, 4, and 6 nerves) through medial longitudinal bundle.
    • These regulate the vestibuloocular reflexes.
    • Fibers to anterior horn cells of spinal cord through vestibulospinal tract and helps in the coordination of head, neck, and eye muscles.
  • The cochlear nuclei consist of two: the ventral and dorsal nuclei and lies in the floor of fourth ventricle.

Vestibulocochlear Nerve Course And Relations

  • The vestibular nerve begins in the vestibular ganglion (Scarpa’s ganglion) located at the lateral end of internal acoustic meatus
  • The peripheral processes change the origin of the neurons pass through the foramina in the lateral end of the internal acoustic meatus and supply the ampullary crista and the maculae
  • The central processes of the ganglion cells unite to form the trunk of vestibular nerve
  • The nerve then enters the posterior cranial fossa and passes through the cerebellopontine angle to reach the brainstem
  • It enters the brainstem at the pontomedullary junction slightly lateral and posterior to the facial nerve
  • The peripheral processes of the bipolar neurons of spiral ganglion (present in modiolus) innervate the hair cells in the organ of Corti
  • The central processes of the bipolar neurons pass through the tractus spiralis foraminous at the medial end of the internal acoustic meatus and assemble to form the cochlear nerve
  • The cochlear nerve passes through the pontocerebellar angle to reach the lateral aspect of the pontomedullary junction
  • It enters the pons and divides into ascending and descending fibers, which terminate in ventral and dorsal nuclei in the floor of the fourth ventricle.

Vestibulocochlear Nerve Auditory Pathway

  • The hair cells are innervated by the dendrites of bipolar cells of the spiral ganglion and the axons of this form the cochlear part of the VIII cranial nerve and end in cochlear nuclei.
  • From the cochlear nuclei the main nuclei in the auditory pathways, from below upwards are:
    • Superior olivary complex
    • Lateral lemniscus
    • Inferior colliculus
    • Medial geniculate body
    • Auditory cortex.
  • The auditory fibers travel via the ipsilateral and contralateral routes and have multiple decussation points and as a result, each ear is represented in both cerebral hemispheres
  • The auditory cortex concerned with hearing is situated in the superior temporal gyrus (Brodmann’s area 41).

Vestibulocochlear Nerve Clinical Testing

  • The vestibular part is clinical examined by asking for tinnitus and vertigo and look for nystagmus
  • The cochlear part is tested by Rinne’s test, Weber’s test, and Absolute bone conduction test.

Vestibulocochlear Nerve Applied

  • Disturbances of vestibular nerve function include giddiness (Vertigo) and Nystagmus
  • Vestibular nystagmus is an uncontrollable rhythmic oscillation of the eyes
  • This form of nystagmus is essentially a disturbance in the reflex control of the extraocular muscles, which is one of the functions of the semicircular canals
  • The causes of vertigo include diseases of the labyrinth, lesions of the vestibular nerve and the cerebellum, multiple sclerosis, tumors, and vascular lesions of the brainstem
  • Disturbances of the cochlear nerve function produce deafness and tinnitus
  • Loss of hearing may be due to a defect of the auditory conducting mechanism in the middle ear, damage to the receptor cells in the spiral organ of Corti in the= cochlea, lesions of the cochlear nerve due to acoustic neuroma and trauma, or lesion of the cerebral cortex of temporal lobe due to multiple sclerosis.

Question 7. Write a note on the glossopharyngeal nerve.
Answer:

Glossopharyngeal nerve

  • It is the 9 nerve
  • It is a mixed nerve and consists of both sensory and motor fibers but predominantly it is sensory.

Cranial Nerves Course And Distribution Of Glossopharyngeal Nerve

Glossopharyngeal Nerve Functional Components

  • General somatic afferent (GSA) fiers carry proprioceptive sensations from the stylopharyngeus and skin of auricle and terminate in nucleus of spinal tract of the nerve
  • General visceral afferent (GVA) fibers carry general sensations of pain, touch, and temperature from the mucous membrane of pharynx, tonsil, soft palate, and posterior 1/3rd of tongue and terminate in dorsal nucleus of vagus
  • General visceral efferent (GVE) fibers (preganglionic parasympathetic) arise from the inferior salivatory nucleus and they supply secretomotor fibers to parotid gland
  • Special visceral afferent (SVA) fibers carry taste sensations from posterior 1/3rd of tongue including vallate papillae and terminate in nucleus tractus solitarius
  • Special visceral effrent (SVE) fibers arise from nucleus ambiguus and supply stylopharyngeus muscle.

Cranial Nerves Glossopharyngeal Nerve

Glossopharyngeal Nerve Nuclei: The nuclei includes the following

  • Nucleus ambiguus (branchiomotor)
  • Inferior salivatory nucleus (parasympathetic)
  • Nucleus of tractus solitaries (gustatory).

Glossopharyngeal Nerve Course And Relations

  • The nerve arises from the upper part of the posterolateral sulcus of medulla between olive and inferior cerebellar peduncle as 3–4 rootlets just above rootlets of vagus nerve
  • The rootlets unite to form a single trunk which passes forwards and laterally cross the jugular tubercle and reaches the jugular foramen
  • It leaves the cranial cavity through middle part of jugular foramen enclosed in a separate dural sheath
  • The nerve consists of a small superior ganglion and a larger inferior ganglion
  • The superior ganglion lies within the jugular foramen and the inferior ganglion lies just below the jugular foramen
  • In the jugular foramen the nerve lies in a deep groove leading to the cochlear canaliculus and is separated from the 10th and 11th cranial nerves by inferior petrosal sinus
  • After emerging through the jugular foramen the nerve passes downwards and forwards between internal carotid artery and internal jugular vein. It then descends anterior to internal carotid artery and styloid process to reach the lower border of stylopharyngeus and it pass along with the stylopharyngeus through the gap between superior and middle constrictors
  • It then curves around the lateral border of stylopharyngeus and supplies it and gives of the pharyngeal branches and then passes deep to the stylohyoid ligament and posterior end of hyoglossus and divide into terminal branches tonsillar and lingual branches which supply the mucous membrane of tonsil, pharynx, and tongue.

Cranial Nerves Course And Distribution Of Glossopharyngeal Nerve Flow Chart

Glossopharyngeal Nerve Branches and Distribution: T branches include

  • Tympanic branch: It arises from the inferior ganglion and enters the middle ear through the tympanic canaliculus and takes part in the tympanic plexus and gives of the following branches:
    • Lesser petrosal nerve which carries the preganglionic fibers to the otic ganglion
    • To supply middle ear, mastoid antrum, and auditory tube.
  • Carotid nerve: It is a branch to carotid body and sinus
  • Pharyngeal branches: They take part in the pharyngeal plexus along with the pharyngeal branches of vagus and cervical sympathetic chain
  • Branch to stylopharyngeus: It is the only muscular branch of the glossopharyngeal nerve and supply the stylopharyngeus muscle
  • Tonsillar branches: Supplies the tonsil, fauces, and palate
  • Lingual branches: Supplies the posterior 1/3rd of the tongue and vallate papillae and carries the taste and general sensations.

Glossopharyngeal Nerve Clinical Testing: The nerve is clinically tested by

  • Eliciting the gag reflex: On stroking the posterior wall of pharynx there is a reflex contraction of pharyngeal muscles causing gagging
  • Testing the taste sensations in the posterior 1/3rd of tongue.

Glossopharyngeal Nerve Applied

  • Isolated glossopharyngeal nerve lesions are extremely rare, as the last four cranial nerves are not often damaged and even if they are, they are commonly affected together, for example by a tumor in posterior cranial fossa.
  • Complete lesion of glossopharyngeal nerve can result in:
    • Loss of taste and general sensations over posterior
    • 1/3rd of tongue
    • Difficulty in swallowing
    • Loss of salivation from parotid gland.

Question 8. Write a note on vagus nerve.
Answer:

Vagus nerve

  • It is the 10 cranial nerve
  • It is called so because of the extensive or vague course through the head, neck, thorax, and abdomen.
  • It is a mixed nerve consisting of both sensory and motor fibers but predominantly it is motor.
  • The fibers of the cranial root of the accessory nerve are also distributed through vagus nerve.
  • The nerve bears two ganglia: superior and inferior.
  • The superior ganglion is round and lies in the jugular foramen whereas the inferior is cylindrical and lies near base of skull.

Cranial Nerves Territory Of Distribution Of Vagus Nerve In The Neck, Throax And Abdomnen

Cranial Nerves Vagus Nerve

Abbreviations: GSA = General somatic affrent; SVA = Special visceral affrent; GVE = General visceral effrent; SVE = Special visceral effrent

Vagus Nerve Functional Components:

  • General somatic afferent (GSA) fiers (peripheral processes of neurons of superior ganglion) carry general sensations from skin of the auricle and terminate in the nucleus of the spinal tract of the trigeminal nerve
  • General visceral afferent (GVA) fiers (peripheral processes of neurons of inferior ganglion) carry general sensations from mucous membrane of the pharynx, larynx, trachea, esophagus, and thoracic and abdominal viscera and terminate in the nucleus tractus solitarius, and some in the dorsal nucleus of the vagus
  • General visceral efferent (GVE) fibers arise from dorsal motor nucleus of vagus and provide parasympathetic innervation to thoracic and abdominal viscera
  • Special visceral afferent (SVA) fibers carry taste sensations from posterior 1/3rd of tongue and epiglottis and terminate in the nucleus tractus solitarius
  • Special visceral efferent (SVE) fibers arise from nucleus ambiguus and supply muscles of the palate, pharynx, and larynx.

Vagus Nerve Nuclei

  • The nuclei associated with vagus nerve include the following:
  • The nucleus of spinal tract of trigeminal
  • Nucleus tractus solitarius (gustatory) is distributed through internal laryngeal nerve to taste buds of epiglottis and vallecula
  • Dorsal nucleus of vagus (parasympathetic) is a mixed nucleus and its fibers form the main bulk of the nerve
  • Nucleus ambiguus (branchiomotor) is mainly a part of cranial root of the accessory nerve.

Vagus Nerve Course and Relations

  • It arises from the posterolateral sulcus of the medulla between the olive and inferior cerebellar peduncle as 5–10 rootlets below and in line of the rootlets of the glossopharyngeal nerve
  • The rootlets unite to form a large trunk that passes laterally and cross the jugular tubercle and reaches the jugular foramen
  • It then leaves the cranial cavity by passing through middle part of the jugular foramen along with 11th nerve as enclosed within common dural sheath
  • The superior and inferior ganglia are located on the nerve as it passes through the jugular foramen
  • The superior ganglion which is small and round lies within the foramen and the large cylindrical inferior ganglion lies just below the jugular foramen
  • After coming out through jugular foramen the nerve runs vertically downwards within the carotid sheath and lies first between internal jugular vein and internal carotid artery and then between internal jugular vein and common carotid artery
  • At the root of the neck, the nerve enters the thorax
  • The right vagus enters by crossing the first part of the subclavian artery and then inclines medially behind brachiocephalic vessels and reaches the right side of trachea which separates it from the right pleura
  • It then inclines behind the hilum of the right lung and courses medially toward the esophagus to form the esophageal plexus with the left vagus nerve
  • The left vagus enters thorax by passing between the left common carotid and left subclavian arteries
  • It descends on the left side of the aortic arch, which separates it from the left pleura, and travels behind the phrenic nerve
  • It then courses behind the root of the left lung and then deviates medially and downwards to reach the esophagus and form the esophageal plexus by joining the right vagus nerve
  • The anterior and posterior gastric nerves are then formed from the esophageal plexus
  • The gastric nerves supply all abdominal organs and the gastrointestinal tract ending just before the left colonic (splenic) flexure.

Cranial Nerves Course And Distribution Of Vagus Nerve Flowchart

Vagus Nerve Branches and Distribution

  • The branches of the vagus nerve in head and neck region is as follows:
  • In the jugular foramen the superior ganglion gives of the following branches:
    • Meningeal branch: This supplies the dura of posterior cranial fossa after taking a recurrent course to enter the cranial cavity
    • Auricular branch (Alderman’s nerve): It enters the mastoid canaliculus and emerges through tympanomastoid fissure behind the external auditory meatus to supply the skin on the back of the meatus and adjoining part of auricle. It then enters the meatus between the bony and cartilaginous part to supply the flor and the tympanic membrane
    • Communicating branches to glossopharyngeal and cranial root of accessory nerves and superior cervical ganglion.
  • In the neck it gives of the following branches:
    • The pharyngeal branch arises from the lower part of the inferior ganglion and chiefly contains fibers of the accessory nerve. It passes between external and internal carotid arteries and reaches near the middle constrictor of pharynx and takes part in formation of the pharyngeal plexus. It supplies:
      • All muscles of pharynx except the stylopharyngeus (supplied by glossopharyngeal nerve)
      • All muscles of soft palate except tensor palati (supplied by mandibular nerve).
    • Superior laryngeal nerve arises from the inferior ganglion and runs downwards and forwards on the superior constrictor and reaches the middle constrictor to divide into external and internal laryngeal nerves.
      • The external laryngeal nerve (motor) is a thin nerve that accompanies the superior thyroid artery and pierces the inferior constrictor and supplies the cricothyroid muscle. It also gives branches to the inferior constrictor and pharyngeal plexus
      • The internal laryngeal nerve (sensory) is a thick nerve it passes downwards and forwards and pierces the thyrohyoid membrane and enters larynx and supplies:
        • Mucous membrane of pharynx, epiglottis, vallecula
        • Mucous membrane of larynx up to the level of vocal cords.
    • Carotid branches supply the carotid body and sinus
    • Right recurrent laryngeal nerve arises from the vagus in front of the right subclavian artery and winds around the first part of subclavian artery and then ascends up in the tracheoesophageal groove.
    • Here it is related to inferior thyroid artery. It then passes deep to the inferior constrictor and enters larynx behind the cricothyroid joint and supplies:
      • All intrinsic muscles of larynx except cricothyroid muscle
      • Sensory supply to larynx below vocal cords
      • Branches to trachea and esophagus
      • Inferior constrictor
      • Cardiac branches to the deep cardiac plexus.
      • Cardiac branches: Superior and inferior. They enter thorax through thoracic inlet. Out of the four cardiac branches the left inferior goes to the superficial cardiac plexus and other three go to the deep cardiac plexus.
  • In thorax the left recurrent laryngeal arises in the superior mediastinum and crosses the arch of aorta and hooks below the arch of the aorta on left side of ligamentum arteriosum and reaches tracheoesophageal groove and supplies structures similar to right recurrent laryngeal nerve.

Vagus Nerve Clinical Testing

  • The nerve is tested by asking the patient to open his mouth and say ‘Ah’ and the palatal arches of two sides are compared
  • In normal cases the soft palate rises in the midline
  • In bilateral lesions the soft palate droops
  • In unilateral lesions there is drooping of soft palate on one side and uvula deviates to the normal side.

Vagus Nerve Applied

  • Various branches of the vagus nerve are affected due to lesions
  • Recurrent laryngeal nerve palsies are most common due to malignant disease (25%) and surgical damage (20%) during operations of thyroid gland, neck, esophagus, heart, and lung
  • Because of its longer course, lesions of left are more frequent than those of right
  • High lesions of the vagus nerve, which affect the pharyngeal and superior laryngeal branches, cause difficulty in swallowing as well as vocal cords defects
  • The bilateral lesions can cause:
    • Nasal regurgitation of liquids while swallowing
    • Nasal twang of voice
    • Hoarseness of voice
    • Flattening of palatal arches
    • Cadaveric position of vocal cords
    • Dysphagia.

Question 9. Write a note on accessory nerve.
Answer:

Accessory nerve

  • It is the 11 cranial nerve
  • It is a purely motor nerve and has two roots: Cranial and spinal
  • The cranial root is an accessory to vagus and its fibers are distributed through the vagus nerve
  • The spinal root has an independent course and is regarded as accessory nerve.

Cranial Nerves Accessory Nerve

Cranial Nerves Origin Of Cranial And Spinal Parts Of Accessory Nerve And Course Of Spinal Part Via Posterior Trangle Of Neck

Accessory Nerve Functional Components

  • General somatic efferent (GSE) fibers arise from long spinal nucleus of the accessory nerve and provide motor supply to sternocleidomastoid and trapezius muscles
  • Special visceral efferent (SVE) fibers arise from the nucleus ambiguus and provide motor supply to muscle of soft palate, pharynx, and larynx.

Accessory Nerve Nuclei

  • The cranial root arises from lower part of nucleus ambiguus
  • The spinal root arises from a long spinal nucleus situated on the lateral part of the anterior grey column of the spinal cord of upper fie spinal segments.

Accessory Nerve Course and Relations

  • The Cranial Root
    • It arises as 4–5 rootlets from the posterolateral sulcus of medulla between the olive and inferior cerebellar peduncle
    • These rootlets join to form a trunk and then run laterally to 9th, 10th cranial nerves and spinal root and reach jugular foramen, and joins with spinal root
    • It then gets separated from the spinal root as it emerges from the jugular foramen and finally fuses with vagus nerve at inferior ganglion and gets distributed through branches of vagus.
  • The Spinal Root
    • It arises from the upper fie spinal segments as a row of rootlets between the ventral and dorsal roots
    • These rootlets unite to form a trunk
    • It then ascends upwards to the vertebral canal and enters the cranial cavity through foramen magnum behind the vertebral artery
    • It then reaches the jugular foramen and unites with the cranial root and comes out through middle part of jugular foramen and separates from the cranial root after coming out
    • It then descends vertically downwards between internal jugular vein and internal carotid artery
    • It then turns downwards and backwards at the midway between mastoid process and angle of the mandible and crosses internal jugular vein
    • It is crossed by occipital artery and is accompanied by the sternocleidomastoid branch of the occipital artery and surrounded by lymph nodes
    • It then pierces the sternocleidomastoid muscle at the junction of upper one-fourth and lower three-fourths and communicates with C2 and C3 nerves and supplies the muscle
    • The nerve then enters the posterior triangle after emerging through the posterior border of the sternocleidomastoid and then runs downwards and backward to get embedded in the fascial roof and lies over levator scapulae
    • The nerve leaves the posterior triangle by passing deep to anterior border of trapezius 5 cm above the clavicle and communicates with the C3 and C4 nerves and ends by supplying trapezius.

Cranial Nerves Accessory Nerve Flowchart

Accessory Nerve Distribution

  • The cranial root (via vagus and pharyngeal plexus) supplies:
    • All muscles of palate except tensor palatine and tensor tympani
    • All muscles of pharynx except stylopharyngeus
    • All intrinsic muscles of larynx.
  • The spinal root supplies:
    • Sternocleidomastoid along with C2 and C3 nerves
    • Trapezius along with C3 and C4 nerves.

Accessory Nerve Clinical Testing

  • The sternocleidomastoid muscle is tested by asking the patient to turn his face to the opposite against the resistance offered by examiner’s hand. In normal conditions a person can do it and sternocleidomastoid stands out prominently
  • The trapezius is tested by asking the patient to shrug his shoulder against resistance.

Accessory Nerve Applied

  • Lesions of the spinal part of accessory nerve will result in paralysis of the sternocleidomastoid and trapezius muscles
  • The sternocleidomastoid will atrophy and there will be weakness in turning the head to the opposite side
  • The trapezius muscle will also atrophy and the shoulder will droop on that side, there will also be weakness and difficulty in raising the arm above the horizontal
  • Lesions of the spinal part of the nerve may occur anywhere along its course and mostly results from tumors or trauma from stab or gunshot wounds in the neck.

Question 10. Write a note on hypoglossal nerve.
Answer:

Hypoglossal nerve

  • It is the 12 cranial nerve
  • It is purely a motor nerve.

Cranial Nerves Origin, Course, Communication And Distribution Of Hypoglossal Nerve

Cranial Nerves Hypoglossal Nerve

Hypoglossal Nerve Functional Components: General somatic efferent (GSE) fibers arise from the hypoglossal nucleus and supply all the muscles of the tongue.

Hypoglossal Nerve Nucleus: It is a 2 cm long structure which lies at the floor of fourth ventricle beneath the hypoglossal triangle.

Hypoglossal Nerve Course and Relations

  • It arises from the ventral aspect of medulla from anterolateral sulcus between pyramid and olive as 10–15 rootlets
  • The rootlets are attached in line with the rootlets of ventral root of 1st cervical spinal nerve
  • The rootlets run laterally and pass behind the vertebral artery to form two roots which pierce the dura mater near the hypoglossal canal and enter the hypoglossal canal
  • In the canal the two roots unite to form a single trunk and come out of cranial cavity
  • It then lies deep to internal carotid artery and 10th cranial nerve and passes downwards and laterally and reaches the interval between internal carotid artery and internal jugular vein
  • It then descends vertically up to the level of the angle of the mandible
  • It then curves forwards and crosses the internal and external carotid arteries and loop of lingual artery and reach the posterior margin of hyoglossus muscle and runs on its superfiial surface below the deep part of the submandibular gland
  • At the anterior margin of the hyoglossus muscle, it lies on the genioglossus and then runs forward and upwards up to tip of tongue to supply the muscles.

Cranial Nerves Course And Pathway Of Hypoglossal Nerve Flowchart

Hypoglossal Nerve Branches and Distribution: The nerve gives the following branches:

  • Branches of the hypoglossal proper which supply all muscles of the tongue except palatoglossus which is supplied by the cranial root of accessory nerve
  • Branches of the hypoglossal nerve containing C1 fiers which includes:
    • Meningeal branch: After coming through the hypoglossal canal it takes recurrent course and enters the cranial cavity and supplies the dura of posterior cranial fossa
    • Descendens hypoglossal or upper root of ansa cervicalis: It arises while crossing the internal carotid artery and runs downwards to join the inferior root of ansa cervicalis
    • Nerve to thyrohyoid: It crosses the greater cornu of the hyoid bone to reach the muscle
    • Nerve to geniohyoid: It arises from above the hyoid bone.

Hypoglossal Nerve Clinical Testing

  • To assess the hypoglossal nerve, the genioglossus muscles are assessed
  • The patient is asked to protrude the tongue
  • If the nerve of both sides is intact the tongue lies in the midline
  • If the hypoglossal nerve of one side is damaged the tongue deviates to side of the lesion due to unopposed action of muscles of normal side
  • If nerves of both sides are affected the patient is unable to protrude the tongue.

Hypoglossal Nerve Applied

  • Infranuclear hypoglossal nerve lesion causes unilateral lingual paralysis and hemiatrophy. The protruded tongue deviates to the paralyzed side on retraction.
  • The wasted and paralysed side also rises higher than the unaffected side. Lesions of the hypoglossal nerve may occur anywhere along its course and may result from tumor, demyelinating diseases, syringomyelia, and vascular accidents
  • In case of supranuclear lesions there is paralysis without wasting. The tongue moves sluggishly resulting in defective speech and on protrusion the tongue deviates to opposite side. Fasciculation can also be present.

Cranial Nerves Multiple Choice Question And Answers

Question 1. All of the following structures pass through the jugular foramen except:

  1. Glossopharyngeal nerve
  2. Vagus nerve
  3. Inferior petrosal sinus
  4. Hypoglossal nerve

Answer: 4. Hypoglossal nerve

Question 2. All of the following are muscle not supplied by glossopharyngeus except:

  1. Palatopharyngeus
  2. Salpingopharyngeus
  3. Stylopharyngeus
  4. Superior constrictor of pharynx

Answer: 3. Stylopharyngeus

Question 3. All of the following branches of left vagus arise in neck except:

  1. Pharyngeal branch
  2. Branch to carotid body
  3. Recurrent laryngeal
  4. Cardiac branches

Answer: 3. Recurrent laryngeal

Question 4. In lesions of right hypoglossal nerve:

  1. Tongue deviates to right side on protrusion
  2. Tongue deviated to left side on protrusion
  3. Tongue fails to protrude at all
  4. None of the above

Answer: 1. Tongue deviates to right side on protrusion

Question 5. The incorrect statement about accessory nerve is:

  1. Its both roots arise from the medulla
  2. Its cranial root is distributed through vagus nerve
  3. Its spinal root supplies sternocleidomastoid and trapezius
  4. It exits skull through jugular foramen

Answer: 1. Its both roots arise from the medulla