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