12 - Cranial Nerves

what are the types of cranial nerves?

sensory - conveying information about the outside environment to the brain

motor - provide innervation to muscles that provide motion

both - both sensory and motor functions

what are the types of sensory categories?

general sensation - touch temperature, pain vibration

special sensory - sight, smell, taste, hearing/balance (specific organ)

visceral sensory - baroreceptors, stretch receptors (not aware)

what are the motor categories?

somatic

branchial - muscles of facial expression, mastication muscles, upper trap, SCM

visceral - salivary glands, parasympathetic

what to ask for each cranial nerve?

location level in brainset?

where is ventricular system and cerebrospinal fluid?

where is the sulcus limitans? (nucleus medial to SL → motor, lateral → sensory)

what CN are in the cerebrum?

olfactory, optic

what CN are in the midbrain?

oculomotor, trochlear

what CN are in the pons?

trigeminal, abducens, facial, vestibulocochlear

what CN are in the medulla?

glossopharyngeal, vagus, accessory, hypoglossal

sulcus limitans

divides spinal cord into functional regions, neural tube differentiates into 2 major zones during development alar plate (sensory) and basal plate (motor)

also in brainstem - lateral is sensory, medial is motor

order of types of sensory and motor information in the alar and basal plates?

lateral to medial:

alar plate: somatic sensory, special visceral sensory, general visceral sensory

basal plate: general visceral sensory, special visceral sensory, somatic sensory

cranial nerve functions and motor/sensory/both

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CN I name, type, fxn, origin, cranial fossa

sensory

fxn: smell

o: cerebellum

one of the few CN that can regenerate, derived from telencephalon

cribriform plate

where are cell bodies and neurons of CN I?

cell bodies in olfactory area, neurons are in mucosa. branches of olfactory nerve pass from nasal cavity to cribriform plate of ethmoid bone by sending axons to the bulb. bulb overlies cribriform plate of ethmoid bone in skull

where does the olfactory nerve synapse? pathway?

glomerulus - each glomerulus responds to a different smell

glomerulus synapses on to mitral cell which carries information to higher areas (limbic, hypothalamus)

cilia in nose → olfactory receptor → up through cribriform plate → synapses on glomeruli (specialized) → mitral cells → axons of mitral cells that make olfactory tract → cerebrum

CN II name, type, fxn, origin, cranial fossa

optic

sensory

fxn: vision

o: cerebrum

optic canal

CN II pathway

neural fibers originate from photoreceptors of retina → fibers converge at optic disc forming optic nerve → optic nerve leaves orbit through optic canal → at floor of middle cranial fossa, some optic fibers of each nerve crosses to other side forming optic chiasm → nerve synapses with visual relay centers of brain

optic nerve test

red reflex - can reveal problems in the cornea lens and sometimes the vitreous, L and R must be equal

CN III name, type, fxn, o, cranial fossa

oculomotor

motor

fxn: eye movement, constricts pupil, lens accommodation (all eye muscles except for SO4, RL6)

o: midbrain

superior orbital fissure

PERLA

pupils equally round and reactive to light and accomodating

CN IV name, type, fxn, origin, cranial fossa

trochlear

motor - general somatic motor n

fxn: moves eye down and out, innervates superior orbital

o: midbrain

superior orbital fissure

what is the only CN that exits the brainstem dorsally?

trochlear CN IV, goes around cerebral peduncle and courses ventrally out

does the trochlear nerve decussate?

yes,

how to test for CN IV?

follow my finger

CN V name, type, fxn, origin, cranial fossa

trigeminal

both motor and sensory

fxn: muscles of mastication and sensation to face

o: pons, originates in relation to pons and forms trigeminal ganglion lateral to the cavernous sinus

ophthalmic V1 - superior orbital fissure, maxillary V2 - foramen rotundum, mandibular V3 - foramen ovale

trigeminal ganglia is similar to _____.

dorsal root ganglia

what are the 3 neurons that work together to transmit sensation?

1 - DRG or trigeminal ganglio

2 - dorsal horn or principal nucleus of V OR spinal nucleus of V

3 - thalamus - then up to cerebral cortex up to appropriate place in the homunculus

what is the purpose of having multiple synapses?

areas of inhibition or facilitation - less synapses within the motor system has less need for modification

dermatomes of V1, 2, 3?

V1 ophthalmic - forehead, orbit, nose

V2 maxillary - zygomatic region and upper lip

V3 mandibular - lower lip, skin of mandible

how to test for trigeminal nerve?

sensation of dermatomes

CN VI name, type, fxn, origin, cranial fossa

abducens

motor

fxn: abducts eye (lateral rectus)

o: pons, ponto-medullary junction

superior orbital fissure

what is the facial colliculus

facial nerve wraps around abducens nucleus creating a bump over the nucleus (seen in rhomboid fossa - posteriorly)

CN VII name, type, fxn, origin, cranial fossa

facial

both motor and sensory

fxn: muscles of facial expression and taste anterior 2/3 of tongue

o: pons, brainstem as 2 separate division, large primary root carries motor fibers and smaller intermediate nerve carries sensory and parasympathetic fibers

internal acoustic meatus

facial nerve pathway

internal acoustic meatus → facial canal in petrous portion of temporal bone → 2 divisions join and form facial nerve and leave cranium via stylomastoid foramen

testing facial nerve

corneal reflex - touch cornea and eyelid should close (efferent part)

facial expressions

CN VIII name, type, fxn, origin, cranial fossa

vestibulocochlear

sensory

fxn: vestibular - mediates balance and motion, cochlear - enable hearing

o:

internal acoustic meatus

CN IX name, type, fxn, origin, cranial fossa

glossopharyngeal

both motor and sensory

fxn: saliva secretion, taste posterior ½ of tongue, gag reflex

o: medulla

jugular foramen

CN IX test

swallowing

CN X name, type, fxn, origin, cranial fossa

vagus

both motor and sensory

fxn: throat sensation, swallowing, coughing, elevates soft palate during “ahh”

o: medulla

jugular foramen

what is the longest cranial nerve and the only CN to leave neck and head region?

CN X vagus

what nerve travels into thoracic and abdominal cavities and provides parasympathetic supply to visceral organs?

CN X vagus

axons that supply motor to larynx are from _____.

nucleus ambiguus

what are the 2 ganglia of CN X?

superior and inferior ganglion of vagus nerve

superior: fibers for general sensory afferent function

inferior: fibers for special sensory (larynx, esophagus, lungs, trachea) and visceral output

CN XI name, type, fxn, origin, cranial fossa

accessory

motor

fxn: innervates SCM and traps

o: medulla, cervical spinal cord combine with those from medulla and then come back inferiorly to innervate the muscle below

jugular foramen

CN XI test

resisted rotation for SCM, resisted shoulder shrug

CN XII name, type, fxn, origin, cranial fossa

hypoglossal

motor

fxn: tongue movements

o: medulla, originates from hypoglossal nucleus in caudal medulla

hypoglossal foramen

what CN runs deep in submandibular region innervating extrinsic and intrinsic muscles of the tongue?

CN XII hypoglossal

CN XII test

sticking tongue out