Oct4 M3-Cranial Nerves Lecture 2 Flashcards
most imp thing to remember about CN III (oculomotor n.)
it DOESN’T inn. lateral rectus m. (bc this is done by CN VI) and the superior oblique m. (CN IV)
facial n. fct
- movements of the face (has 5 branches each for diff muscles)
- efferent arm of the corneal reflex
how to examine for facial n. dysfunction
ask pt to
- raise eyebrows
- smile
- blow up their cheeks
- close their mouth
- pucker the lips
- LOOK FOR ASYMMETRY*
relation between CN VI and VII
- VII nucleus is in the pons (lat to VI, near the pons-medulla junction)
- VII loops around the nucleus of VI causing a bump in the 4th ventricle called the facial colliculus
- travels with VIII (can’t distinguish them)
- both VII and VIII move laterally up to the ear
- VII travels up the skull to a bony canal in the temporal bone and comes out of skull in opening behind the ear called the internal auditory meatus (also part of the temporal bone) (VIII also travels there)
- comes forward and inn. facial muscles
(NOT ON EXAM) 3 other nuclei and fcts of CN VII
borrows 3 nuclei and their axons travel in CN VII for VII to do certain fcts
- axons from superior salivatory nucleus: PSS to lacrimal (eye) and salivary glands
- axons from spinal nucleus of CN V: sensation to skin behind the ear
- axons of nucleus (of tractus) solitarius: taste to anterior two third of the tongue
- for sensation and taste, the sensory info travels from periphery, in axons of CN VII to finally reach their nucleus and synapse in nucleus of CN V*
unique feature of the VII
sparing of the forehead in UMN lesions (bc the facial nucleus containing LMNs receives bilateral UMN inn. from the cortex)
so what is special is that the forehead has the only muscles controlled by CN VII that receive ipsilateral UMNs to their LMNs (+ contralateral UMNs) and NOT JUST CONTRALATERAL
cause of one sided facial weakness with sparing of the forehead
lesion of contralateral UMNs to CN VII
cause of Bell’s palsy, which is a complete facial weakness (including forehead) of one side of the face
lesion of the ipsilateral LMN from CN VII
what causes the lesion of the ipsilateral LMNs from CN VII in Bell’s palsy (what damages the CN VII)
a viral infection with edema and swelling of the nerve within the tight bony canal (it gets strangulated)
function of CN VIII (vestibulocochlear n.)
is almost 2 nn stuck together
- cochlear branch for hearing
- vestibular branch for balance
what pts with vestibulocochlear n. lesion complain about
- hearing loss
- tinnitus (ear ringing, buzzing)
- vertigo (unpleasant sensation of spinning)
how to test for CN VIII lesion
- rub two fingers near pt ear to test hearing (cochlear fct)
- tuning fork to test between conductive vs sensorineural hearing loss (cochlear fct)
- look for abnormal eye movements (vestibular fct) *bc vestibular system imp for reflexes maintaining eye position while head and body are moving)
pathway vestibulocochlear n. takes
- nucleus lat to VI and VII in the pons, near junction to medulla (caudal pons)
- travels with VII
- both VII and VIII move laterally up to the ear
- VII and VIII travel up the skull to a bony canal in the temporal bone and comes out of skull in opening behind the ear called the internal auditory meatus (also part of the temporal bone) (both VII and VIII do all that)
unique thing about VIII
- cerebello-pontine angle = angle between cerebellum and pons
- important anatomical location bc BENIGN tumors can occur there and affect CN VIII
- meningiomas (benign tumor of meninges) and schwannomas (benign tumor of Schwann cells that myelinate CN VIII)
what patients complain of in glossopharyngeal n. lesion (CN IX)
pain bc IX has imp sensory function (along with many imp fcts)
- trigeminal neuralgia was in the face
- glossopharyngeal neuralgia is in the throat (irritation of CN IX)
nuclei of the IX
doesn’t have its own nucleus. borrows 4 nuclei
- nucleus ambiguus (motor inn. to stylopharyngeus m. but all other pharynx m. inn by X)
- inferior salivatory nucleus (PSS to parotid gland)
- nucleus (of the tractus) solitarius (carotid body and sinus info + taste to post third of tongue)
- spinal nucleus of V (larynx and pharynx sensation + touch (non taste) sensation for post third of tongue)
- ARE NUCLEI IN THE MEDULLA*
touch and taste to posterior third of the tongue
- touch = IX, spinal nucleus of V
- taste = IX, nucleus of tractus solitarius
touch and taste to anterior two thirds of the tongue
- touch = CN V
- taste = CN VII (nucleus of tractus solitarius)
(imp) how we test for IX dysfunction
gag reflex (tests for both IX and X) = touch back of someone's throat (pharynx) on one side. and their palate moves upwards SYMMETRICALLY normally. (IX = afferent arm. connects in brainstem to both X nerves. X = efferent arm = m. contraction). -note: some people have very weak gag reflex so absent reflex is not helpful
IX path taken
- moves posteriorly, level lower than n. V, VI and VII exit
- exits in same place as X and XI (at the jugular foramen)
fcts of vagus n. (X)
- inn. m. of pharynx and larynx
- supplies sensation to multiple areas
- inn all viscera
- etc
what pts complain about in vagus n. lesion
- dysarthria (problems speaking)
- dysphagia (prob swallowing)
- NO problems in viscera bc 2 vagus n. to viscera but each vagus n. to muscles on its side only*
how to test for X lesion
gag reflex + listen to pt speech (slurring of speech with weakness of pharynx and larynx)
direct and consensual response in gag reflex (touch one side of pharynx)
- direct = contraction (elevation) of ipsilateral palate
- consensual response = contraction (elevation) of contralateral palate
- same as corneal reflex*
IX n. lesion consequence on gag reflex
nothing happens at all (on both sides). signal doesn’t get to X nerves
