HONORS ANATOMY & PHYSIOLOGY

THE CRANIAL NERVES

CRANIAL NERVES

12-pairnamed “cranial” because each passes thru a

foramina of the craniumpart of PNSeach with roman numeral (order from

anterior posterior in which nerves arise from base of brain) & a name that indicates nerve distribution

CRANIAL NERVES

classified as:1. sensory2. motor3. mixed (sensory & motor)

Cranial Nerve I: Olfactory

olfact = to smellsensoryolfactory epithelium on superior surface of

nasal cavity just inferior to cribiform plate of ethmoid bone

olfactory receptors are bipolar neurons each: single odor-sensitive dendrite their unmyelinated axons join above plate form rt or lt olfactory nerves

Course of Olfactory Nerve

olfactory nerves end in pair of olfactory bulbs: masses of gray matter resting just above cribiform plate where they synapse with next neurons in olfactory pathway

Course of Olfactory Nerve

axons of these neurons make up the olfactory tracts posteriorly to primary olfaction center in temporal lobe

Cranial Nerve II: Optic Nerve

optic = eyesensoryrods & cones in retina: receptors initiating

visual signals & relay them bipolar cells optic ganglion neurons their axons join forming optic nerves

pass thru optic foramen optic chiasm: a cross-over of medial half of each eye to opposite side (lateral half does not cross

Optic Chiasm

Optic Tracts

from optic chiasm optic tracts most axons thalamus synapse with

neurons whose axons primary visual area of occipital lobe

some axons synapse with motor neurons in midbrain extrinsic eye muscles

Cranial Nerve III: Oculomotor

oculo = eyemixed, mainly motorits motor nucleus in

ventral part of midbrain

2 branches pass thru superior orbital fissure

Superior Branch Inferior Branch

axons innervate:1. superior rectus2. levator palpebrae

superioris (upper eyelid)

axons innervate:1. medial rectus2. inferior rectus3. inferior oblique

Oculomotor Nerve Extrinsic Muscles of Eye

Oculomotor Nerve

inferior branch also: parasympathetic innervation to intrisic

muscle of eye (smooth muscle)1. ciliary muscle: adjusts lens for near/far

vision

2. circular muscle of iris: contracts/relaxes in response to amt of light (pupils constrict/dilate)

Oculomotor Nerve: Sensory

proprioception: nonvisual perception of movements & positions of body

Cranial Nerve IV: Troclear Nerve

trochle = pulleymixed, mainly motorsmallest of the 12 cranial nervesonly 1 that arises from posterior of midbrain

Cranial Nerve IV: Troclear Nerve

motor:axons from nucleus in midbrain superior

orbital fissureinnervates superior oblique muscle

sensory: proprioception in superior oblique

Cranial Nerve IV: Troclear Nerve

Trigeminal Nerve V

largest of 12 cranial nervesmixed:

sensory: ganglion in temporal bone motor: neurons in pons

Cranial Nerve V: Trigeminal Nerve

tri: has 3 branches1. Ophthalmic: sensory only: upper eyelids,

eyes, lacrimal glands, upper nasal cavity, side of nose, forehead, anterior ½ of scalp

2. Maxillary: sensory only: mucosa of nose, palate, part of pharynx, upper teeth, upper lip, lower eyelids

3. Mandibular: sensory: anterior 2/3 of tongue (not taste), cheek, lower teeth

motor: muscles of mastication

Trigeminal Nerve

Cranial Nerve VI: Abducens Nerve

ab: away / ducens: to lead (nerve impulses causes abduction of eyeball)

mixed mainly motornucleus in pons (motor): innervates lateral

rectus musclesensory: proprioception in lateral rectus

Abducens Nerve

On Which Side is VI not Functioning?

Cranial Nerve VII: Facial Nerve

mixedsensory:

taste buds anterior 2/3 of tongue, proprioceptors in face & scalp

motor: nucleus in pons innervates muscles of facial expression +

stylohyoid muscle & posterior belly of digastric muscle

parasympathetic: lacrimal glands, palatine glands, salivary glands: sublingual & sub-mandibular

Facial Nerve

Cranial Nerve VIII: Vestibulocochlear Nerve

vestibule:small cavity; cochlear: snail-likemixed, mainly sensory2 branches1. Vestibular:

equilibrium2. Cochlear:

hearing motor: hair cells of spiral organ

Cranial Nerve IX: Glossopharyngeal Nerve

glosso:tongue, pharyngeal: throatMixedsensory: taste buds & somatic sensory

receptors on posterior 1/3 tongue, proprioceptors in swallowing muscles, baroreceptors (stretch) in carotid sinus, chemoreceptors in carotid bodies

motor: from nuclei in medulla, exit thru jugular foramen, innervate stylopharyngeus muscle (elevates pharynx & larynx)

parasympathetic: motor: stimulate parotid gland to secrete saliva

Cranial Nerve X: Vagus Nerve

vagus: wanderer, vagrantmixeddistributed from head abdomen

Vagus Nerve

sensory: skin of external ear taste buds in epiglottis & pharynx proprioceptors in muscles of neck & throat baroreceptors in arch of aorta &

chemoreceptors in aortic bodies visceral sensory receptors in most organs of

thorax & abdominal cavities

Vagus Nerve

parasympathetic motor: heart & lungs glands in GI tract smooth muscle of airways, esophagus,

stomach, gall bladder, small intestine, most of large intestine

Distribution of Vagus Nerve

Cranial Nerve XI: Accessory Nerve

mixedoriginates from both the brainstem & spinal

cordcranial root:

motor: from medulla thru jugular foramen supplies voluntary muscles of pharynx,

larynx, & soft palatespinal root:

mixed, mainly motor motor:

Cranial Nerve XI: Accessory Nerve

spinal root: mixed, mainly motor motor: neurons in anterior gray horn of C1 –

C5 axons come together foramen magnum jugular foramen

innervates sternocleidomastoid & trapezius muscles

sensory: proprioceptors in muscles it supplies

Cranial Nerve XII: Hypoglossal

hypo: below, glossal: tonguemixedsensory:proprioceptors in tongue muscles

medullamotor: nucleus in medulla hypoglossal

canal muscles of the tongue (speech, swallowing)

Development of the Nervous System

begins developing in 3rd wk from a thickening of ectoderm called the neural plate

Development of the Brain & Spinal Cord