16 CRANIAL NERVES AND THEIR NUCLEI: SCHEMATIC VIEW FROM ABOVE

236



Regional Neuroscience

Medial dissection



Accessory oculomotor (Edinger-Westphal) nucleus



Red nucleus



Oculomotor nucleus



Oculomotor nerve (III)



Trochlear nucleus

Trochlear nerve (IV)



Mesencephalic nucleus of trigeminal nerve



Abducens nucleus

Trigeminal nerve (V)

and ganglion



Internal genu of facial nerve



Facial nucleus



Principal sensory nucleus of trigeminal nerve



Vestibular nuclei

Motor nucleus of trigeminal nerve



Anterior and posterior cochlear nuclei



Facial nerve (VII)

Superior and inferior salivatory nuclei

Vestibulocochlear nerve (VIII)

Abducens nerve (VI)



Solitary tract nucleus



Glossopharyngeal nerve (IX)

Posterior (dorsal) nucleus of vagus nerve (X)

Hypoglossal nerve (XII)



Hypoglossal nucleus



Vagus nerve (X)



Nucleus ambiguus



Accessory nerve (XI)*



Spinal nucleus of accessory nerve



Olive

Efferent fibers

Spinal tract and spinal nucleus of trigeminal nerve



Afferent fibers

Mixed fibers



*Evidence suggests that the accessory nerve lacks a cranial root and has no connection to the vagus nerve.

Verification of this finding awaits further investigation.



11.17  CRANIAL NERVES AND THEIR

NUCLEI: SCHEMATIC LATERAL VIEW

CN III exits from the ventral and medial surface of the midbrain. CN IV is the only CN to exit from the dorsal surface of

the brain stem, in the midbrain near the pons-midbrain junction. CN V exits from the lateral surface of the mid pons. CN

VI exits from the pons medially, just rostral to the medullopontine junction. CNs VII and VIII exit from the cerebellopontine angle at the junction of the medulla and pons. CNs IX

and X exit from the lateral part of the medulla and are joined

by CN XI, which ascends through the foramen magnum. CN

XII exits medially from the preolivary sulcus. These CN sites

of entry and exit are important localizing features in the brain

stem that permit regional localization of lesions resulting from

vascular insults, tumors, and degenerative disorders.

CLINICAL POINT

The CN nuclei that contain LMNs are found in two longitudinal columns, including a medial column (CN nuclei III, IV, VI, and XII) and



a lateral column (motor CN nuclei V, VII, and nucleus ambiguus).

These LMN groups are found in the CNS and send axons into the

peripheral nervous system to synapse on their appropriate groups of

skeletal muscles using acetylcholine, and they exert important trophic

influences on their innervated muscles. An LMN lesion (bulbar polio,

amyotrophic lateral sclerosis, and other LMN palsies) results in total

paralysis of the affected muscle; atrophy is caused by denervation, loss

of tone, and loss of reflexes. Denervated muscles commonly demonstrate denervation hypersensitivity, with resultant fibrillation as seen

on an electromyogram. As LMNs die (particularly conspicuous in

amyotrophic lateral sclerosis) their agonal electrical responses occur

as spontaneous discharges of individual motor units (an LMN and its

innervated muscle fibers); each discharge produces a visible fasciculation (or twitch). With some LMN disorders such as polio, if enough

neighboring LMNs survive, their axons can sprout and reinnervate

previously denervated skeletal muscle fibers; this process must occur

within approximately 1 year, or the atrophy becomes permanent. In

UMN paralysis, in which the LMNs do not die, the affected muscle

fibers are not denervated; reflexes are brisk, tone is increased with

passive stretch (spasticity), and pathological reflexes (plantar extensor

response) are seen.



Brain Stem and Cerebellum



Supratrochlear nerve

Medial rectus muscle



Medial branch

Lateral branch



of supraorbital nerve



237



Superior View



Levator palpebrae superioris muscle



Superior oblique muscle



Superior rectus muscle



Nasociliary nerve



Eyeball

Lacrimal gland



Cribriform plate of ethmoid bone



Supraorbital nerve



Common annular tendon



Lacrimal nerve



Optic (II) nerve



Lateral rectus muscle

Frontal nerve



Optic chiasm



Ophthalmic nerve

Maxillary nerve



Pituitary stalk (infundibulum)



Meningeal branch of maxillary nerve



Oculomotor (III) nerve



Mandibular nerve



Trochlear (IV) nerve



Meningeal branch (nervus spinosus) of mandibular nerve



Abducens (VI) nerve

Tentorial (meningeal) branch

of ophthalmic nerve



Lesser petrosal nerve

Greater petrosal nerve

Tentorium cerebelli



Trigeminal ganglion



11.18  NERVES OF THE ORBIT

CN II carries visual information from the ipsilateral retina. Axons from the temporal hemiretinas remain ipsilateral, whereas

axons from the nasal hemiretinas cross the midline in the optic chiasm. All axons then enter the optic tract. CNs III (from

oculomotor nuclei), IV, and VI innervate the extrinsic muscles

of the eye. Sensory portions of the ophthalmic division of V

supply general sensation to the cornea and eyeball and provide

the afferent limb of the corneal reflex. Motor fibers of CN VII

innervate the orbicularis oculi muscle, closing the eye; these

fibers constitute the efferent limb of the corneal reflex.



CLINICAL POINT

CN II (the optic nerve) is a CNS tract myelinated by oligodendroglia.

It can be damaged by demyelinating disease (optic neuritis in multiple sclerosis), by optic nerve gliomas, by ischemic injury (central

retinal artery), or by trauma (sphenoid fracture). The resultant defect

is �ipsilateral blindness or a scotoma (blind spot). The ipsilateral nature of the deficit rules out optic chiasm, optic tract, or central visual

lesions. The retina also is CNS tissue and can undergo neurodegenerative changes. Macular degeneration involves damage to the coneintensive regions of the retina (macula) and leads to the inability to

read and the loss of acuity. Increased intracranial pressure can result

in papilledema, a condition in which pressure pushes the optic nerve

head inward (toward the center of the eyeball), producing a swollen

appearance on ophthalmoscopy. This process takes 24 hours to occur after onset of intracranial pressure; the presence of papilledema is

used diagnostically to identify intracranial pressure.



238



Regional Neuroscience



A. Superior view with extraocular muscles partially cut away

Supratrochlear nerve (cut)



Levator palpebrae superioris muscle (cut)

Superior rectus muscle (cut)



Medial and lateral

branches of

supraorbital nerve (cut)



Lacrimal nerve (cut)



Infratrochlear nerve



Short ciliary nerves



Anterior ethmoidal nerve



Branch of oculomotor nerve to inferior oblique muscle



Long ciliary nerves



Ciliary ganglion



Optic (II) nerve



Motor (parasympathetic) root from oculomotor nerve



Posterior ethmoidal nerve



Sympathetic root from internal carotid plexus



Nasociliary nerve



Sensory root from nasociliary nerve



Ophthalmic nerve



Branches to medial and inferior rectus muscles



Trochlear (IV) nerve (cut)



Abducens (VI) nerve (to lateral rectus muscle)



Oculomotor (III) nerve



Inferior division of oculomotor nerve

Superior division of oculomotor nerve



Abducens (VI) nerve



B. Coronal section through the cavernous sinus

Optic chiasm

Internal carotid artery

Diaphragma sellae

Oculomotor (III) nerve

Trochlear (IV) nerve

Pituitary gland

Internal carotid artery

Abducens (VI) nerve

Ophthalmic nerve

Cavernous sinus

Maxillary nerve



11.19╇NERVES OF THE ORBIT (CONTINUED)

Parasympathetic preganglionic fibers from the nucleus of Edinger-Westphal distribute to the ciliary ganglion, which supplies the pupillary constrictor muscle and the ciliary muscle

(accommodation for near vision). Preganglionic parasympathetic axons from the superior salivatory nucleus distribute

to the pterygopalatine ganglion, which supplies the lacrimal

gland (tear production). Sympathetic postganglionic nerve

fibers from the superior cervical ganglion supply the pupillary dilator muscle and the superior tarsal muscle (damage

results in mild ptosis). CNs III, IV, VI, and V (ophthalmic and

�maxillary divisions) traverse the cavernous sinus and are vulnerable to damage by cavernous sinus thrombosis.

CLINICAL POINT

The extraocular nerves can be damaged by trauma, vascular infarcts,

tumors, aneurysms, pressure (compression of CN III against the free



edge of the tentorium with transtentorial herniation), or other pathology. Oculomotor palsy (CN III) results in paralysis or weakness of

the medial rectus, superior and inferior rectus, inferior oblique, and

�levator palpebrae superioris muscles. The most conspicuous deficit is

the inability to adduct the ipsilateral eye, a lateral strabismus (resulting

from unopposed action of the lateral rectus), and diplopia. Damage to

the levator palpebrae superioris muscle results in profound ptosis of

the ipsilateral eye. Lesions in CN III also disrupt the outflow from the

Edinger-Westphal nucleus to the ciliary ganglion, producing a fixed

(unresponsive) and dilated ipsilateral pupil.

A lesion in CN IV (trochlear) results in paralysis or weakness of the

superior oblique muscle. This muscle is a depressor of the eye when it is

directed nasally. Thus, a patient has difficulty walking down stairs and

stepping off curbs and has trouble reading while lying down. The patient tries to compensate for a lesion in CN IV by turning the head away

from the side of the lesion to avoid having to use the paralyzed muscle.

A lesion in CN VI (abducens) results in paralysis or weakness of

the ipsilateral lateral rectus muscle, with a resultant medial strabismus

and diplopia upon attempted lateral gaze.



Brain Stem and Cerebellum



239



Short ciliary nerves

Edinger-Westphal nucleus

Long ciliary nerve

(autonomic)

Oculomotor (III) nerve

Optic (II) nerve

Oculomotor nucleus

Ciliary ganglion

Sensory root of ciliary ganglion

Trochlear nucleus

Sympathetic root of ciliary ganglion

Superior division of oculomotor nerve

Abducens nucleus

Frontal nerve

Superior and inferior colliculi

Lacrimal nerve

Nasociliary nerve

Ophthalmic nerve



Superior oblique muscle

Superior rectus muscle

Levator

palpebrae

superioris

muscle

Superior

tarsal muscle

(involuntary)



Sphincter

pupillae

muscle

Dilator

pupillae

muscle

Abducens (VI) nerve

Ciliary muscle



Trochlear (IV) nerve



Pterygopalatine ganglion



Oculomotor (III) nerve



Inferior division of

oculomotor nerve



Inferior oblique muscle



Mandibular nerve



Medial rectus muscle



Infraorbital nerve

Zygomatic nerve



Internal carotid artery and plexus

Maxillary nerve



Inferior rectus muscle

Motor (parasympathetic) root of ciliary ganglion



Lateral rectus muscle and abducens nerve

(turned back)

Cavernous plexus

Common annular tendon



Levator palpebrae

superioris muscle

Superior rectus muscle

Oculomotor (III) nerve



Medial rectus muscle

Inferior rectus muscle

Inferior oblique muscle



11.20  EXTRAOCULAR NERVES (III, IV, AND VI)

AND THE CILIARY GANGLION: VIEW IN

RELATION TO THE EYE

CN VI innervates the lateral rectus muscle; damage results

in ipsilateral paralysis of lateral gaze. CN IV innervates the

superior oblique muscle; damage results in inability to look

in and down (most conspicuous when climbing stairs, stepping off a curb, reading in bed). CN III (oculomotor �nuclei)

innervates the medial rectus, superior rectus, �inferior rectus,



{

Lateral rectus muscle { Abducens (VI) nerve



Superior oblique muscle Trochlear (IV) nerve



Motor fibers

Sensory fibers

Sympathetic fibers

Parasympathetic fibers



and inferior oblique muscles (damage results in paralysis of

the ipsilateral medial gaze) and also innervates the levator

palpebrae superioris muscle (damage results in profound

ptosis). The ciliary ganglion gives rise to postganglionic

parasympathetic axons that supply the pupillary constrictor

muscle and the ciliary muscle; damage results in a fixed and

dilated pupil that does not constrict for the pupillary light

reflex and does not accommodate to near vision.



240



Regional Neuroscience



Motor fibers

Sensory fibers



Ophthalmic nerve



Proprioceptive fibers



Tentorial (meningeal) branch



Parasympathetic fibers

Sympathetic fibers



Trigeminal (V) nerve and

trigeminal (semilunar) ganglion



Nasociliary nerve

Sensory root of ciliary ganglion

Lacrimal nerve

Frontal nerve

Ciliary ganglion



Motor nucleus of trigeminal nerve

Mesencephalic nucleus of trigeminal nerve

(proprioception)

Principal sensory nucleus of

trigeminal nerve (discriminatory sensation)



Posterior ethmoidal nerve



Spinal tract and spinal

nucleus of trigeminal nerve

(pain and temperature)



Long ciliary nerve

Short ciliary nerves

Supratrochlear nerve

Supraorbital nerve (medial

and lateral branches)

Anterior ethmoidal nerve

Infratrochlear nerve

External nasal and internal nasal

(medial and lateral rami) branches

of anterior ethmoidal nerve

Maxillary nerve

Meningeal branch

Zygomaticotemporal nerve

Zygomaticofacial nerve

Zygomatic nerve

Infraorbital nerve



Facial (VII) nerve



Ganglionic branches and

pterygopalatine ganglion

Superior alveolar branches

(anterior, middle, posterior)

of infraorbital nerve

Nasal branches (posterosuperior lateral, nasopalatine

and posterosuperior medial)



Chorda tympani

Superficial temporal

branches

Articular and

auricular branches



Nerve of pterygoid canal



Auriculotemporal nerve



Pharyngeal branch



Parotid branches



Palatine nerves; major

(anterior), minor

(middle and posterior)



Meningeal (nervus spinosus) branch

Lesser petrosal nerve

(from glossopharyngeal nerve)



Deep temporal nerves (anterior,

middle, and posterior) to

temporalis muscle



Tensor tympani nerve



Lateral pterygoid and

masseteric nerves



Otic ganglion



Buccal nerve

Mental nerve

Tensor veli palatini and

medial pterygoid nerves

Inferior dental plexus (inferior

dental and gingival nerves)



Trigeminal Nerve (V)



Inferior alveolar nerve



Lingual nerve Submandibular

ganglion



Mylohoid nerve (to mylohyiod and

anterior belly of digastric muscles)

Mandibular nerve