The cranial nerves do not directly relate to the eye, except for the optic nerve (CN II). The 12 pairs of cranial nerves originate from the brain and leave the cranial cavity through openings. The olfactory (CN I), optic (CN II), and vestibulocochlear (CN VIII) nerves are entirely sensory. The facial (CN VII) nerve contains motor, sensory, and parasympathetic components. The glossopharyngeal (CN IX) and vagus (CN X) nerves are mixed nerves containing motor, sensory and parasympathetic fibers. The hypoglossal nerve (CN XII) is a pure motor nerve that supplies the muscles of the tongue.

1. CRANIAL NERVES NOT
DIRECTLY RELATED TO
THE EYE
Othman Al-Abadi, M.D

2. Cranial Nerves
• Twelve pairs of cranial nerves originate from nuclei within the brain and leave the cranial
cavity through foramina or fissures.
• All are distributed in the head & neck except the 10th which also supplies structures in
the thorax & abdomen.
• The cranial nerves are: I Olfactory, II.Optic,
III Oculomotor, IV Trochlear, V Trigeminal,
VI Abducent, VII Facial, VIII Vestibulocochlear,
IX Glossopharyngeal, X vagus,
XI Accessory, and the XII Hypoglossal
• The I, II, & VIII nerves are entirely sensory.
• The III, IV, VI, XI & XII nerves are entirely
motor.
• The V, VII, IX & X nerves are mixed sensory
& motor.
• The III, VII, IX & X nerves contain visceral parasympathetic component supplying smooth
muscles & glands.

5. Olfactory Nerve
• Is a purely sensory nerve.
• It arises from receptors of olfactory neurons located in the upper posterior
part of the nasal cavity above the superior concha.
• The olfactory neurons are bipolar cells with coarse peripheral dendrites and
long central processes forming olfactory nerves which pass through the
cribriform plate of ethmoid bone and ending in the olfactory bulb.
• The olfactory bulb consists mainly of large mitral cells with few small tufted
& granular cells.
• The dendrites of mitral cells synapse with the incoming olfactory nerve
fibers forming rounded areas called synaptic glomerulus. Also the tufted &
granular cells synapse with mitral cells.

6. • The mitral cells also synapse with axons from contralateral olfactory bulb
through the olfactory tract.
• Axons of ipsilateral mitral & tufted cells and few axons form contralateral
olfactory bulb form the olfactory tract located in the olfactory sulcus on the
orbital surface of frontal lobe.
• The olfactory tract proximal to the anterior perforated substance divides
into medial & lateral olfactory striae.
• The lateral olfactory stria terminates in the olfactory areas of temporal
cerebral cortex. These areas represent the primary olfactory cortex.
• The primary & secondary olfactory areas are responsible for appreciation of
olfactory sensations.
• The olfactory pathway consists of two order neurons & has no connection
with the thalamus.

8. • The primary olfactory cortex has connections with brain centers which evoke
emotional & autonomic responses to olfactory stimuli.
• Anosmia is loss of olfactory sensation.
• Bilateral temporary anosmia usually occurs in common cold & allergic
rhinitis.
• Unilateral anosmia results from damage to olfactory nerve, bulb or tract…
fractures to the ant cranial fossa involving the cribriform plate can result in
tear of the olfactory nerve.
• Unilateral lesion of cortical olfactory area usually has no impairment of
olfactory sensation as the olfactory pathway from each nasal cavity is
bilaterally presented in the cerebral cortex.

10. Facial Nerve
• Is a mixed nerve contains motor, sensory & parasympathetic components.
• Emerges from the pons anteriorly to accompany CN-VIII through the
internal acoustic meatus… it enters the facial canal & runs through the inner
ear… on reaching the medial wall of the middle ear, it turns sharply
backward & descends in the posterior wall of the middle ear to emerge
through the stylomastoid foramen.
• The facial nerve has three nuclei:
1.Main motor nucleus:
• Lies within the pons.
• The part supplying the upper face receives corticonuclear fibers from both
hemispheres… while the part supplying the lower face receives
corticonuclear fibers from the opposite hemisphere.
• Motor fibers arise from the motor nucleus located in the pons and
supplies muscles of facial expression, stapedius, stylohyoid & posterior
belly of digastric.

12. 2. Parasympathetic Nuclei:
• They are the superior salivatory and lacrimal nuclei.
• The superior salivatory nucleus receives afferent fibers from the
hypothalamus, & supplies the submandibular & sublingual glands
• The lacrimal nucleus supplies the lacrimal gland… it receives afferent
fibers from the hypothalamus for emotional responses and from the
sensory nucleus of the trigeminal nerve for reflex lacrimation secondary to
irritation of the cornea or conjunctiva.
3. Sensory Nucleus :
• This is the upper part of the nucleus of the tractus solitarius.
• Sensations of taste travel from the anterior 2/3rd of the tongue & the floor
of the mouth & palate through the peripheral axons of cells situated in the
geniculate ganglion of the seventh cranial nerve. Efferent fibers cross the
midline and ascend to the thalamus to the taste area of the cortex.

17. TheVestibulocochlear Nerve
• Is a pure sensory nerve which consists of two distinct
parts, the cochlear nerve & the vestibular nerve.

18. The Cochlear Nerve
• It conducts nerve impulses concerned with sound from the organ of corti in
the cochlea.
• The fibers of the cochlear nerve are the central processes of nerve cells
located in the spiral ganglion of the cochlea.
• On entering the pons, the nerve fibers divide with one branch enter the
posterior cochlear nucleus and the other enter the anterior cochlear nucleus.
• The majority of the fibers of 2nd order neuron of cochlear nuclei cross the
median plane and pass to the trapezoid body and superior olivary nucleus
and ascend as tract called the lateral lemniscus, while few fibers remain
uncrossed ascending in ipsilateral lateral lemniscus.
• On reaching the midbrain, the fibers either terminate in the nucleus of the
inferior colliculus or are relayed in the medial geniculate body and pass to
the auditory cortex of the cerebral hemisphere in the superior temporal gyrus.

21. The Vestibular Nerve
• Conducts nerve impulses from the utricle, saccule, and the semicircular
canals that provide information concerning the position and movement of the
head.
• The nerve fibers of the vestibular nerve are the central processes of nerve
cells located in the vestibular ganglion, which is situated in the internal
acoustic meatus… it emerges from the internal acoustic meatus with the
cochlear nerve & crosses the posterior cranial fossa with the facial nerve.
• Enters the anterior surface of the brainstem between the pons & medulla
oblongata.
• They enter the vestibular nuclear complex of the medulla and the fibers then
divide into short ascending and long ascending fibers. A few fibers pass
directly to the cerebellum bypassing the vestibular nuclei.

24. The Vestibular Nerve
• The vestibular nuclear complex consists of a group of nuclei situated below
the floor of the 4th ventricle. Four nuclei may be recognized: the superior,
inferior, medial and lateral vestibular nuclei.
• These nuclei receive afferent fibers from the vestibular nerve and from the
cerebellum. Efferent fibers from the nuclei pass to the cerebellum while other
fibers descend from the lateral nucleus uncrossed to the spinal cord forming
the vestibulospinal tract.
• In addition, efferent fibers pass to the nuclei of the oculomotor, trochlear, and
abducent nerve through the medial longitudinal fasciculus. These connections
enable the movements of the head and the eyes to be coordinated so that
visual fixation on an object can be maintained.
• Ascending fibers also pass upward from the vestibular nucleus to the post-
central gyrus of the cerebral cortex after first synapsing in the thalamus…
they consciously orient the individual in space.

25. • Testing vestibular function
• Integrity Caloric tests: inc. & dec. temp of the external
auditory meatus (through endolymph of the semicircular
canals.
• Function vertigo & nystagmus
• Testing cochlear function
• Integrity whispered voice or vibrating tuning fork
(weber & rinne tests)
• Function deafness & tennitus

26. The Glossopharyngeal Nerve
• Is a mixed motor and sensory nerve with a parasympathetic component.
• Leaves the skull through the jugular foramen.
• The nerve has three nuclei, the main motor, the parasympathetic and the
sensory nuclei.
• The motor nucleus lies in the medulla and is formed by the superior end of
the nucleus ambiguus. It receives corticonuclear fibers from both cerebral
hemispheres. The efferent fibers supply the stylopharyngeus muscle.
• The parasympathetic nucleus is called the inferior salivatory nucleus. It
receives afferent fibers from the hypothalamus. The efferent preganglionic
parasympathetic fibers reach the otic ganglion and the postganglionic fibers
pass to the parotid gland.

29. The Glossopharyngeal Nerve
• The sensory nucleus is part of the nucleus of the tractus solitarius.
• It receives general sensation & taste from posterior 1/3rd of the tongue&
pharynx & from the carotid sinus (baroreceptor) & carotid body
(chemoreceptor).
• Sensations of taste travel through the peripheral axons of nerve cells situated
in the ganglion on the glossopharyngeal nerve.
• The central processes of these cells synapse on nerve cells in the nucleus.
Efferent fibers cross the median plane and ascend to the opposite thalamus &
from there to the cerebral cortex.

30. The Glossopharyngeal Nerve
• Afferent information concerning common sensation enters the
brainstem through the superior ganglion of the
glossopharyngeal nerve but ends in the spinal nucleus of the
trigeminal nerve.
• Afferent impulses from the carotid sinus also travel with the
glossopharyngeal nerve and terminate in the nucleus of the
tractus solitarius and are connected to the dorsal motor nucleus
of the vagus nerve.
• The carotid sinus reflex assists in the regulation of arterial blood
pressure.

31. The Vagus Nerve
• Is a mixed motor and sensory nerve with a parasympathetic component.
• Exit the skull through the jugular foramen.
• It supplies the heart, great thoracic vessels, larynx, trachea, bronchi, lungs,
alimentary tract from the pharynx to 2/3rd of colon, liver, kidneys &
pancreas.
• Has three nuclei;
• The motor nucleus lies within the medulla and is formed by the nucleus
ambiguus. It receives corticonuclear fibers from both cerebral hemispheres.
• The efferent fibers supply the constrictor muscles of the pharynx and the
intrinsic muscles of the larynx.

33. The Vagus Nerve
• The parasympathetic nucleus forms the dorsal nucleus of vagus… It receives
afferent fibers from the hypothalamus.
• The efferent fibers are distributed to the involuntary muscles along its course.
• The sensory nucleus is the lower part of the nucleus of the tractus
solitarius. Sensations of taste from most of the posterior part of the tongue
travel through the peripheral axons of nerve cells located in the inferior vagal
ganglion on the vagus nerve. The central processes synapse with nerve cells of
the nucleus.
• Efferent fibers cross the median plane and ascend to the opposite thalamus &
the to the postcentral cortex.

34. The Vagus Nerve
• The function can be tested by the gag reflex (pharyngeal)… the
soft palate can be tested by sayn “aaah” while noticing the soft
palate rise & the uvula moving back in the midline.

36. TheAccessory Nerve
• Is a purely motor nerve that is formed by union of a cranial and a
spinal root.
• The cranial root is formed from the axons of the nucleus ambiguus.
• Receives corticonuclear fibers from both cerebral hemispheres.
• Distributed with the vagus nerve to supply muscles of soft palate,
pharynx & larynx.
• Fibers of spinal accessory nerve arise from the spinal nucleus, which
is situated in the anterior gray column of the upper five cervical
segments of the spinal cord (C1- C5) and supply the trapezius &
sternocleidomastoid muscles.

38. TheAccessory Nerve
• Receives corticonuclear fibers from both cerebral hemispheres.
• The nerve fibers emerge from the spinal cord to form a trunk
that ascends into the skull through the foramen magnum… it
joins the cranial root & both exit through the jugular foramen
then they re-separate.
• The cranial root joins the vagus & is distributed in its
pharyngeal & recurrent laryngeal branches to the muscles of the
soft palate, pharynx & larynx.
• The spinal runs downward & laterally to supply the
sternocleidomastoid & trapezius

39. The Hypoglossal Nerve
• Is a pure motor nerve that arises from the hypoglossal nucleus
in the medulla at the level of the lower part of the 4th ventricle.
• Leaves the skull through hypoglossal canal.
• The hypoglossal nerve supplies all intrinsic & extrinsic muscles
of the tongue except ??
• Paralysis of the hypoglossal nerve result in atrophy of
ipsilateral half of tongue and once the tongue is protruded it
deviates to the side of lesion due the unopposed action of the
opposite normal genioglossus.

41. • Extrinsic
• Genioglossus
• Hyoglossus
• Styloglossus
• Palatoglossus
• Intrinsic
• Superior longitudinal
• Inferior longitudinal
• Vertical
• Transverse