cranial nerves anatomy, a neurosurgical aspect, basis of neurosurgical approaches

1. Anatomy of the Cranial
Nerves
Dr Mukhtar
Neurosurgery
HMC

2. Classification
 Pure Sensory Function: CN I, II
and VIII
 Pure Motor Function: CN III, IV,
VI, XII
 Mixed (Sensorimotor): CN V,
VII, IX, X, XI

3. Cranial nerves nuclei
 Somatic Motor and Branchiomotor
nuclei:
 Axons of nerve cells situated within
the brain
 Nuclei which innervate striated
muscles
 Nerve cell with its fibres is called
Lower Motor Neuron
 Receive impulses from cortex
through corticonuclear fibres
 Bilateral connections except for part
of facial nucleus and a part of

4. Cranial nerves nuclei
 General Visceral Motor nuclei:
 Cranial outflow of the parasympathetic
portion of the autonomic nervous
system
 Edinger-Westphal Nucleus of CN III
 Superior salivatory and lacrimal nuclei of
CN VII
 Inferior salivatory nucleus of CN IX
 Dorsal motor nucleus of CN X
 These nuclei receive numerous afferent
fibres, including descending pathways
from the hypothalamus

5. Cranial nerves nuclei
 Sensory Nuclei of the Cranial Nerves
 Include visceral and somatic
sensory nuclei
 afferent parts of a cranial nerve
are the axons of nerve cells
outside the brain and are situated
in ganglia on the nerve trunks or
the sensory organs.
 First, second and third order
neurons

6. The Olfactory Nerves
 Course:
 Olfactory hair 
Olfactory receptor cells 
Central processes 
Olfactory nerve fibres

Olfactory bulb 
Olfactory tract 
Primary Olfactory Cortex (peri-
amygdaloid & prepiriform cortex) 
Entorhinal area of
parahippocampal gyrus
(Secondary Olfactory Cortex)

9. Optic Nerve
 Origin: The fibres of the optic nerve are the axons
of the cells in the ganglionic layer of the retina.
 Optic Chiasma: situated at the junction of the
anterior wall and floor of the third ventricle
 Optic tract: The optic tract emerges from the optic
chiasma and passes posterolaterally around the
cerebral peduncle. fibres terminate by synapsing
with nerve cells in the lateral geniculate body, while
some fibres pretectal nucleus and superior
colliculus

10. Optic nerve
 Lateral Geniculate Body: small, oval swelling
projecting from the pulvinar of the thalamus. Six
layers of cells.
 Optic Radiation: Fibres of the optic radiation are
the axons of the nerve cells of the lateral geniculate
body. The tract passes posteriorly through the
retrolenticular part of the internal capsule .
 The visual association cortex (areas 18 and 19) is
responsible for recognition of objects and
perception of colour and terminates in the visual
cortex (area 17).

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12. Oculomotor Nerve
 The Oculomotor Nuclei:
 Two nuclei: i) main motor nucleus:
situated in the anterior part of the gray matter
that surrounds the cerebral aqueduct of the
midbrain
 Oculomotor nucleus receives
corticonuclear fibres from both
cerebral hemispheres
 receives tectobulbar fibres from the
superior colliculus
ii) Edinger-Westphal nucleus:
situated posterior to the main
oculomotor nucleus
axons of the nerve cells, which are
preganglionic, accompany the other
oculomotor fibres to the orbit

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14. Oculomotor Nerve
 Course:
 emerges at the anterior surface of midbrain
 passes between posterior cerebral and sup.
Cerebellar arteries
 Lateral wall of cavernous sinus
 Divides into superior and inferior rami
 Enters the orbit

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16. Trochlear nerve
 Trochlear nucleus:
 It lies inferior to the oculomotor nucleus at the
level of the inferior colliculus
 The nerve fibres, pass posteriorly around the
central gray matter to reach the posterior
surface of the midbrain
 Course:
 emerges from the midbrain and immediately
decussates with the nerve of the opposite side
 lateral wall of the cavernous sinus and enters
the orbit through the superior orbital fissure

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19. Trigeminal Nerve

20. Trigeminal nerve
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24. Abducens Nerve

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27. Facial nerve
 Nuclei:
 Main motor nucleus:
 lies deep in the reticular formation of the lower
part of the pons
 The part of the nucleus that supplies the
muscles of the upper part of the face receives
corticonuclear fibres from both cerebral
hemispheres
 The part of the nucleus that supplies the
muscles of the lower part of the face receives
only corticonuclear fibres from the opposite
cerebral hemisphere.

28. Facial nerve
 Nuclei:
 Parasympathetic nuclei:
 Parasympathetic nuclei lie posterolateral to the
main motor nucleus
 Superior salivatory and lacrimal nuclei
 Sensory nucleus
 upper part of the nucleus of the tractus
solitarius and lies close to the motor nucleus
 Sensations of taste travel through the
peripheral axons of nerve cells situated in the
geniculate ganglion on the seventh cranial
nerve

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31. Facial nerve
 Course:
 Sesory and motor components
 fibers of the motor root first travel
posteriorly around the medial side of the
abducent nucleus
 They then pass around the nucleus
beneath the colliculus facialis in the floor
of the fourth ventricle and, finally, pass
anteriorly to emerge from the brainstem
 The sensory root (nervus intermedius) is
formed of the central processes of the
unipolar cells of the geniculate ganglion

32. Facial nerve
 Course:
 It also contains the efferent preganglionic
parasympathetic fibers from the parasympathetic nuclei
 They pass laterally in the posterior cranial fossa with
the vestibulocochlear nerve and enter the internal
acoustic meatus in the petrous part of the temporal
bone
 At the bottom of the meatus, the nerve enters the facial
canal and runs laterally through the inner ear
 On reaching the medial wall of the tympanic cavity, the
nerve expands to form the sensory geniculate ganglion
and turns sharply backwards.
 At the posterior wall of the tympanic cavity, the facial
nerve turns downward on the medial side of the aditus
of the mastoid antrum, descends behind the pyramid,
and emerges from the stylomastoid foramen

33. Facial nerve
 Distribution:
 The motor nucleus supplies the muscles of facial
expression, the auricular muscles, the
stapedius, the posterior belly of the digastric,
and the stylohyoid muscles
 The superior salivatory nucleus supplies the
submandibular and sublingual salivary glands
and the nasal and palatine glands. The lacrimal
nucleus supplies the lacrimal gland
 The sensory nucleus receives taste fibers from
the anterior two-thirds of the tongue, the floor of
the mouth, and the palate

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36. Vestibulocochlear Nerve
Consists of two distinct parts, the vestibular nerve and
the cochlear nerve
 Vestibular Nerve
 conducts nerve impulses from the utricle and saccule
that provide information concerning the position of
the head
 central processes of nerve cells located in the
vestibular ganglion, which is situated in the internal
acoustic meatus
 They enter the anterior surface of the brainstem in a
groove between the lower border of the pons and the
upper part of the medulla oblongata
 When they enter the vestibular nuclear complex, the
fibres divide into short ascending and long
descending fibres; some fibres pass directly to the
cerebellum through the inferior cerebellar peduncle,

37. Vestibulocochlear nerve
 The Vestibular Nuclear Complex
 Four nuclei may be recognized:
 the lateral vestibular nucleus,
 the medial vestibular nucleus
 the superior vestibular nucleus,
 the inferior vestibular nucleus
 Efferent fibers from the nuclei pass to the
cerebellum through the inferior cerebellar
peduncle

38. Vestibulocochlear nerve
 Efferent fibers also descend uncrossed to
the spinal cord from the lateral vestibular
nucleus and form the vestibulospinal tract
 In addition, efferent fibers pass to the nuclei
of the oculomotor, trochlear, and abducent
nerves through the medial longitudinal
fasciculus
 Ascending fibers also pass upward from the
vestibular nuclei to the cerebral cortex, to
the vestibular area in the postcentral gyrus
just above the lateral fissure

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43. Vestibulocochlear nerve
 Cochlear Nerve
 The cochlear nerve conducts nerve impulses
concerned with sound from the organ of Corti in
the cochlea
 The fibres of the cochlear nerve are the central
processes of nerve cells located in the spiral
ganglion of the cochlea
 Entering pons at the level of the facial nerve
 Nerve fibres are distributed to anterior and
posterior cochlear nuclei
 Efferent fibers are relayed through various nuclei
to the auditory cortex

44. Glossopharyngeal Nerve
 Nuclei:
 The glossopharyngeal nerve has three nuclei:
 the main motor nucleus,
 the parasympathetic nucleus, and
 the sensory nucleus
 Course:
 The glossopharyngeal nerve leaves the anterolateral
surface of the upper part of the medulla oblongata as
a series of rootlets in a groove between the olive and
the inferior cerebellar peduncle
 leaves the skull through the jugular foramen
 Descends along internal jugular vein and artery and
supplies the stylopharyngeus, the upper two
constrictor oesophageal muscles, posterior 3rd of the
tongue and pharynx.

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47. Vagus nerve
 Nuclei:
 Main motor
 Sensory
 Parasympathetic
 Course:
 Leaves anterolateral surface of
medulla
 Leaves the skull through jugular
foramen
 Superior and Inferior sensory

48. Vagus Nerve
 Descends down in the neck inside
the carotid sheath
 In the thorax, it contribute to the
pulmonary plexus, cardiac plexus
and nerves of the larynx.
 In the upper abdomen it forms
anterior and posterior gastric
nerves

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52. Accesory nerve
 The accessory nerve is a motor nerve
that is formed by the union of a cranial
and a spinal root.
 Cranial Root
 formed from the axons of nerve cells of
the nucleus ambiguus
 The nucleus receives corticonuclear
fibers from both cerebral hemispheres
 The efferent fibers of the nucleus
emerge from the anterior surface of the
medulla oblongata between the olive
and the inferior cerebellar peduncle

53. Accessory nerve
 Course of the cranial part:
 The nerve runs laterally in the
posterior cranial fossa and joins
the spinal root
 Exits through the jugular foramen
 The roots then separate, and the
cranial root joins the vagus nerve
and is distributed in its pharyngeal
and recurrent laryngeal branches

54. Accessory nerve
 Course of the spinal part:
 Formed by the spinal nucleus in the
upper part of the spinal cord
 Receives corticospinal fibres from
cerebral cortex
 The spinal root emerges from the
cervical spinal cord and ascends into
the skull to join the cranial part.
 Descending down it supplies the
sternocleidomastoid and trapezius
muscles

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56. Hypoglossal nerve
 The hypoglossal nerve is a motor nerve that
supplies all the intrinsic muscles of the tongue
as well as the styloglossus, the hyoglossus,
and the genioglossus muscles
 The hypoglossal nucleus is situated close to the
midline immediately beneath the floor of the lower part
of the fourth ventricle
 Exits the skull through the hypoglossal canal
 Passes between the internal carotid artery and internal
jugular vein
 Posterior belly of the digastric is supplied
 Passes deep to the mylohyoid muscle lying on the
lateral aspect of hypoglossus muscle
 Joined by fibers of the C1 spinal nerve

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59. Thanks!