Objectives

Describe cranial nerve nuclei location, associated nerve, functional category, function

Nuclei	Location	Associated Nerve	Functional category	Function ^[1]
Accessory nucleus	cervical cord	CN XI	somatic motor	trapezius, sternocleidomastoid
Ambiguus nucleus	medulla	CN IX, X	branchial motor	pharyngeal mm
Superior salivatory nucleus	pons	CN VII	visceral efferent	submandibular glands, sublingual, lacrimal
Trigeminal motor nucleus	pons	CN V	branchial motor	med/lat pterigoid, temporalis, masseter, 4 others
spinal nucleus of trigeminal	pons & medulla	CN V, VII, IX, X	somatic sensory	face; ex. acoustic meatus; tymanic cavity, oral/naso pharynx; auricle
dorsal motor nucleus of X	caudal medulla	CN X	visceral motor	thoracic & abdominal viscera
chief sensory nucleus	pons	CN V	somatic sensory	skin & muscles of head, dura
mesencehalic nucleus of V	pons	CN V	general sensory	masseter mm, muscle spindles
vestibular nucleus	caudal pons, medulla	CN VII	special sensory	vestibular apparatus
trigeminal motor nucleus	pons	CN V	branchial motor	muscles of mastication, tensor tympani
inferior salivary nucleus	rostral medulla	CN IX	visceral motor	parotid gland
facial motor nucleus	pons	CN VII	branchial motor	mm. of facial expression, stapedius, stylohyoid, post. belly of digastric
superior solitary nucleus (NTS)	rostral medulla	CN VII, IX	special sensory	gustatory
inferior solitary nucleus (NTS)	caudal medulla	CN IX	visceral sensory	carotid body, carotid sinus
hypoglossal nucleus	medulla	CN XII	somatic motor	muscles of tongue
cochlear nuclei	rostral medulla	CN VIII	special sensory	cochlea

Number	Nerve	Exit from brain	foramen ^[2]	Function ^[1]
1	Olfactory	olfactory bulb	cribiform plate	smells
2	Optic	optic chiasm	optic canal	sees
3	Occulomotor	ventrorostral midbrain	___?	moves eyes, constricts pupils, accomodates
4	Trochlear	dorsocaudal midbrain	__?	moves eyes
5	Trigeminal	rostral ventrolateral pons	orbital fissure, foramen ovale, foramen rotundum	chews and feels front of head
6	Abducens	caudal ventromedial pons	__?	moves eyes laterally
7	Facial	caudal ventral pons	internal acoustic meatus, stylomastoid foramen	moves the face, tastes, salivates, cries
8	Vestibulocochlear	caudal ventrolateral pons	internal acoustic meatus	hears, regulates balance
9	Glossopharangeal	rostral medulla	jugular foramen	tastes, salivates, swallows, monitors carotid body and sinus
10	Vagus	medulla, dorsolateral to olive	jugular foramen	tastes, swallows, lifts palate, talks, communicates with abdomen
11	Accessory	cervical spinal cord	foramen magnum, jugular foramen	turns head, shrugs shoulders
12	Hypoglossal	medulla, olive	hypoglossal foramen/canal	move tongue

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The facial motor nucleus resides in the pons.
The fiber tract moves dorsomedially to wrap around the medial longitudinal fasciculus and the abducens nucleus
The fiber changes directions to move ventrolaterally and exit the pons.

Jaw Jerk: When the mouth is partially opened and the muscles relaxed, tapping the chin causes the jaw to close. Monosynaptic reflex, in CN V, out CN V. The afferent limb of CN V3 innervating the masseter muscle relays to the mesencephalic nucleus of V. The sensory neuron synapses onto the trigeminal motor nucleus which causes the masseter muscle to constrict via CN V.
Corneal Reflex: Touching the cornea causes blinking of the eyelids (afferent CN V1; efferent CN VII). Disynaptic reflex. The nasocilliary nerve senses touch and relays onto the spinal trigeminal nucleus. An interneuron bilaterally innervates the facial motor nucleus. CN VII innervates the obicularis oculi muscle, which constricts.
Salivation reflex: The tongue relays gustatory sensation through CN 7, 9, or 10 to the rostral solitary nucleus (NTS). The secondary neurons then innervate the salvatory nuclei. Parasympathetic nerves then innervate the pteygopalantine, submandibular, and otic ganglion (via CN 7, 9), which ultimately innervate the salivary glands.
Gag reflex: CN IX sensation in oropharnyx --> Spinal trigeminal nucleus --> interneuron to reticular formation (abdominal gag) and ambiguus nucleus (pharnyx, larnyx) --> CN X innervates pharneal plexus muscles
Cough reflex: Vagus nerve in respiratory tree --> solitary nucleus (caudal) --> "cough center" --> Trigeminal motor nucleus & Ambiguus nucleus & hypoglossal nucleus & sinal motoro cord neurons.

The upper motor neurons corresponding to the upper face (ie frontalis muscle) innervate the facial nerve nuclei bilaterally. The upper motor neurons corresponding to the lower face (ie obicularis oris) innervate contralaterally only.
- Thus, a unilateral stroke in the precentral gyrus will result in a contralateral palsy of the lower face. The upper face will have (near) normal strength.
The facial nerve innervates facial muscles on the ipsilateral face.
- Any lesion of the facial nerve will result in an ipsilateral palsy of both the upper and lower face.

CN III is composed of branchial motor and parasympathetic fibers. The motor fibers are grouped on the inside of the nerve (e.g. the white inner circle); the parasympathetic fibers are grouped in the outside of the nerve (e.g. the yellow outer circle above).
- An ischemic injury will preferentially effect the interior fibers, results in motor defects but normal pupil responses
- A compression injury will preferentially effect exterior fibers --> normal occulomotor movements but pupil dilation

Trigeminal Neuralgia: a brief, severe shooting neuropathic pain in the distribution of CN V.
Idiopathic (micro infarcts of the nerve and demyelination): occurs in elderly
Compression by vein or superior cerebellal artery: elderly
Multiple sclerosis: may be first symptom; women 20 - 40.
Post-herpetic: any age, but more common in the elderly

Interruption of the sympathetic fibers results in miosis and ptosis (because of paralysis of the pupillary dilator muscle and of Müller's muscle, respectively). The lesion may be central, between the hypothalamus and the points of exit of sympathetic fibers from the spinal cord (C8 to T3, mainly T2), or peripheral, in the cervical sympathetic chain, superior cervical ganglion, or along the carotid artery.
CN III palsy results in a exotropia (down and out/lateral strabismus) and paralysis of the medial rectus, superior rectus, inferior rectus and the levator palpebrae superioris muscles.
Horner's syndrome is accompanied by a loss of sweating on the same side as the ptosis. Occulomotor functions are still in tact.

Multiple Cranial Nerve Palsy a nice discussion in Harrison's Internal Medicine that integrates concepts.