cranial nerve for bpt students

Anatomy of the Cranial Nerves

BPT Class

Anwesh Pradhan, MPT

Asst. Prof. NIHS,Kolkata

Cranial nerves

Like spinal nerves, cranial nerves are bundles of

sensory or motor fibers that innervate muscles or

glands; carry impulses from sensory receptors, or

show a combination of these fiber types.

They are called cranial nerves because they emerge

through foramina or fissures in the cranium and are

covered by tubular sheaths derived from the cranial

meninges.

There are twelve pairs of cranial nerves, which are

numbered I to XII, from rostral to caudal, according to

their attachment to the brain and penetration of the

cranial dura. Their names reflect their general

distribution or function.

Cranial nerves

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 hypoglossal nucleus


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


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

Cranial nerves

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

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)

Optic Nerve (CN II)Function: Special sensory (special somatic afferent) that

is, the special sense of vision.

Although they are officially nerves by convention, the optic

nerves (CN II) develop in a completely different manner

from the other cranial nerves. The structures involved in

receiving and transmitting optical stimuli (the optical fibers

and neural retina, together with the pigmented epithelium

of the eyeball) develop as evaginations of the

diencephalon (Moore and Persaud, 2003).

The optic nerves are paired, anterior extensions of the

forebrain (diencephalon) and are, therefore, actually CNS

fiber tracts formed by axons of retinal ganglion cells. In

other words, they are third-order neurons, with their cell

bodies located in the retina.

Cranial nerves

Optic Nerve (CN II)

The nerve passes posteromedially in theorbit, exiting through the optic canal toenter the middle cranial fossa, where itforms the optic chiasm (L. chiasmaopticum). Here, fibers from the nasal(medial) half of each retina decussate inthe chiasm and join uncrossed fibersfrom the temporal (lateral) half of theretina to form the optic tract. The partialcrossing of optic nerve fibers in thechiasm is a requirement for binocularvision, allowing depth-of-field perception(three-dimensional vision).

Optic Nerve (CN II)

Thus fibers from the right halves of both retinas form the left optic tract. The decussation of nerve fibers in the chiasm results in the right optic tract conveying impulses from the left visual field and vice versa. The visual field is what is seen by a person who has both eyes wide open and who is looking straight ahead (Hutchins and Corbett, 2002). Most fibers in the optic tracts terminate in the lateral geniculate bodies of the thalamus. From these nuclei, axons are relayed to the visual cortices of the occipital lobes of the brain.

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Oculomotor Nerve (CN III)Functions: Somatic motor (general somatic efferent) andvisceral motor (general visceral efferent parasympathetic).

Nuclei: There are two oculomotor nuclei, each serving oneof the functional components of the nerve. The somaticmotor nucleus of the oculomotor nerve is in the midbrain.The visceral motor (parasympathetic) accessory (Edinger-Westphal) nucleus of the oculomotor nerve lies dorsal to therostral two thirds of the somatic motor nucleus (Haines,2002).1. 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 cerebralhemispheres

• receives tectobulbar fibres from the superior colliculus

2. Edinger-Westphal nucleus: situated posterior to the main oculomotornucleus

• axons of the nerve cells, which are preganglionic, accompany the otheroculomotor fibres to the orbit

Oculomotor Nerve (CN III)The oculomotor nerve (CN III) provides the following:

Motor to the striated muscle of four of the six extraocular

muscles (superior, medial, and inferior recti and inferior

oblique) and superior eyelid (L. levator palpebrae

superioris); hence the nerve's name.

Proprioceptive to the muscles listed above.

Parasympathetic through the ciliary ganglion to the

smooth muscle of the sphincter of the pupil (L. sphincter

pupillae), which causes constriction of the pupil and

ciliary body, which produces accommodation (allowing

the lens to become more rounded) for near vision.

Oculomotor Nerve (CN III)

CN III is the chief motor nerve to the ocular andextraocular muscles. It emerges from the midbrain,pierces the dura lateral to the sellar diaphragm roofingover the hypophysis, and then runs through the roofand lateral wall of the cavernous sinus.

CN III leaves the cranial cavity and enters the orbitthrough the superior orbital fissure. Within this fissure,CN III divides into a superior division (which suppliesthe superior rectus and levator palpebrae superioris)and an inferior division (which supplies the inferiorand medial rectus and inferior oblique). The inferiordivision also carries presynaptic parasympathetic(visceral efferent) fibers to the ciliary ganglion, wherethey synapse. Postsynaptic fibers from this ganglionpass to the eyeball in the short ciliary nerves toinnervate the ciliary body and sphincter of the pupil.

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Trochlear Nerve (CN IV)

Functions: Somatic motor (general somatic efferent)

and proprioceptive to one extraocular muscle

(superior oblique).

Trochlear nucleus:

The nucleus of the trochlear nerve is located in the

midbrain, immediately caudal to the oculomotor

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

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Trochlear Nerve (CN IV)

The trochlear nerve (CN IV) is the smallest cranialnerve. It emerges from the posterior surface of themidbrain (the only cranial nerve to do so), passinganteriorly around the brainstem, running the longestintracranial (subarachnoid) course of the cranialnerves. It pierces the dura mater at the margin of thecerebellar tentorium (L. tentorium cerebelli) andpasses anteriorly in the lateral wall of the cavernoussinus.

CN IV continues past the sinus to pass through thesuperior orbital fissure into the orbit, where it suppliesthe superior oblique the only extraocular muscle thatuses a pulley, or trochlea, to redirect its line of action(hence the nerve's name).

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Trigeminal Nerve (CN V)

Functions: General sensory(general somatic afferent)and branchial motor (specialvisceral efferent) toderivatives of the 1stpharyngeal arch.

Nuclei: There are fourtrigeminal nuclei one motorand three sensory.

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The trigeminal nerve (CN V) is the

largest cranial nerve.

It emerges from the lateral aspect of the

pons by a large sensory root and a

small motor root. The roots of CN V

are comparable to the posterior and

anterior roots of spinal nerves.

Trigeminal nerve

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CN V is the principal general sensory nerve for the head(face, teeth, mouth, nasal cavity, and dura of the cranialcavity). The large sensory root of CN V is composedmainly of the central processes of the pseudounipolarneurons that make up the trigeminal ganglion. Thetrigeminal ganglion is flattened and crescent shaped(hence its unofficial name, semilunar ganglion) and ishoused within a dural recess (trigeminal cave) lateral tothe cavernous sinus. The peripheral processes of theganglionic neurons form three nerves or divisions:

ophthalmic nerve (CN V1), maxillary nerve (CN V2), andsensory component of the mandibular nerve (CNV3). Maps of the zones of cutaneous innervation by thethree divisions resemble the dermatome maps forcutaneous innervation by spinal nerves. Unlikedermatomes, however, there is little overlap ininnervation by the divisions; lesions of a single nerveresult in clearly demarcated areas of numbness.

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Cranial nerves


The fibers of the motor root of CN V pass inferior to thetrigeminal ganglion along the floor of the trigeminalcave, bypassing the ganglion just as the anterior rootsof spinal nerves bypass the spinal sensory ganglia.They are distributed exclusively via the mandibularnerve (CN V3), blending with the sensory fibers as thenerve traverses the foramen ovale in the cranium;entering branches pass to the muscles of mastication,mylohyoid, anterior belly of the digastric, tensor velipalatini, and tensor tympani, which are derived from the1st pharyngeal arch.

Although CN V conveys no presynaptic parasympathetic(visceral efferent) fibers from the CNS, all fourparasympathetic ganglia are associated with thedivisions of CN V. Postsynaptic parasympathetic fibersfrom the ganglia join branches of CN V and are carriedto their destinations along with the CN V sensory andmotor fibers.

Cranial nerves

Abducent Nerve (CN VI)

Functions: Somatic motor (general somatic efferent

and proprioceptive) to one extraocular muscle (lateral

rectus).

Nucleus: The abducent (L. abducens) nucleus is in the

pons near the median plane.

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The abducent nerves (CN VI) emerge fromthe brainstem between the pons and themedulla and traverse the pontine cisternof the subarachnoid space, straddlingthe basilar artery. Each abducent nervethen pierces the dura to run the longestintradural course within the cranial cavityof the cranial nerves that is, its point ofentry into the dura covering the clivus isthe most distant from its exit from thecranium via the superior orbital fissure.

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During its intradural course, it bends sharplyover the crest of the petrous part of thetemporal bone and then courses through thecavernous sinus, surrounded by the venousblood in the same manner as the internalcarotid artery, which it parallels in the sinus.

CN VI traverses the common tendinous ring (L.anulus tendineus communis) as it enters theorbit (see Chapter 7), running on andpenetrating the medial surface of the lateralrectus, which abducts the eye (this functionbeing the basis for the name of the nerve).

Cranial nerves

Facial nerve (CN VII) 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.

Facial nerve (CN VII) 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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Facial nerve (CN VII)

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

Facial nerve (CN VII) 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

Facial nerve (CN VII)

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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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,

bypassing the vestibular nuclei

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


◦ 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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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

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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Vagus nerve

Nuclei:

◦ Main motor

◦ Sensory

◦ Parasympathetic

Course:

◦ Leaves anterolateral surface of medulla

◦ Leaves the skull through jugular foramen

◦ Superior and Inferior sensory ganglia

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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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

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

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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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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cranial nerve for bpt students

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