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
X n. lesion conseq on gag reflex
- X nerve on one side of pharynx doesn’t cause contraction (elevation) of the palate
- the palate elevates asymmetrically, away from the lesion side (bc the lesion side doesn’t elevate)
- the uvula deviates to the site contralateral to the lesion (bc moves up with other side)
X nucleus
- own nucleus: dorsal motor nucleus (ANS for glands and SM of pharynx, larynx, viscera)
- borrowed = nucleus ambiguus (m. of pharynx and larynx)
- borrowed = nucleus solitarius (aortic stretch and chemoRs)
- borrowed = spinal nucleus of V (some sensation of pharynx and larynx + ear)
unique feature of X
has a branch called the recurrent laryngeal n.
- inn. the m. of the larynx below the vocal folds (hidden by the thyroid cartilage)
- damage (parathyroid or thyroid surgery) prevents opening of vocal cords (procedure there)
- branches off each X near arch of aorta and ascends back to larynx on side of the common carotids
path taken by X
- moves posteriorly, level lower than n. V, VI and VII exit
- exits in same place as IX and XI (at the jugular foramen)
- follows common carotids downwards
- recurrent laryngeal n. (branch of X) follows them back upwards to the mm of larynx below vocal folds
spinal accessory n. (XI) function
innervates 2 muscles
- sternocleidomastoid
- trapezius
XI injury: what pts complain about
- weakness and atrophy of the two muscles
- dysarthria and dysphagia (not related to XI fct) bc there is assoc injury to IX and X bc the problems in IX, X and XI in these pts are caused by pathology in jugular foramen where all three CNs pass
origin of the spinal accessory n. + path taken
- arises from C1 to C4 spinal roots
- ascends through the foramen magnum
- exits the skull with IX and X through the jugular foramen
how we test for spinal accessory n. fct
- test function of sternocleidomastoid m. (not trapeziums bc it gets inn from XI and also directly from C1 to C4 so can’t say lesion in XI for sure if something abnormal)
- right sternocleidomastoid helps turn the head to the LEFT and vice versa (bc pulls back of the head forward)
- can ask patient to turn their head to right and left
nucleus of spinal accessory n. (XI)
- the accessory nucleus
- is in line (longitudinally) with the nucleus ambiguus but is located in anterior horn of spinal cord from C1 to C5
hypoglossal n. (XII) fct
inn. the muscles of the ipsilateral half of the tongue (the tongue has many muscles)
what pts complain about in XII lesion
- tongue atrophy
- tongue fasciculations
- tongue weakness
- difficulty eating
- difficulty swallowing
- difficulty making certain sounds
how to examine hypoglossal n. for lesions
- look at the tongue (may be able to see abnormal NOT smooth surface, cracks, fasciculations)
- ask pt to stick tongue out and look for asymmetry
- unilateral XII lesion = tongue deviates to side of lesion (one half falling)
nucleus of hypoglossal n.
hypoglossal nucleus
- only nucleus of XII
- is a motor nucleus
- on dorsal side of medulla, exits there bilaterally
- exits skull through the hypoglossal canal
anatomical location of CNs 7 to 12
- VI, VII and VIII exit in order from medial to lateral at caudal pons near pons-medulla junction
- IX, X and XI exit medulla bilaterally on the sides of the medulla from rostral to caudal in order
- XII exits medulla medially on ventral surface and seems out of (rostral-caudal) order
(imp) basic brainstem anatomy to know
- midbrain with hourglass (sablier) shape. in superior half of hourglass, superior bilateral lines = superior colliculi, inferior bilateral lines = inferior colliculi and below the inferior colliculi have the cerebral peduncles (all that in sup half of hourglass)
- small pons with glasses shape. contains bilateral middle cerebellar peduncle (connects pons to cerebellum)
- medulla with tree trunk shape
(imp) approx location of CN III nucleus
- midbrain
- lying over superior colliculi
(imp) approx location of CN IV nucleus
- midbrain
- lying over inferior colliculi
(imp) approx location of CN V nucleus
long vertical nucleus spanning length of midbrain, pons and medulla longitudinally to the sup and inf colliculi
(imp) most caudal CN nucleus
11th nerve (spinal accessory) nucleus
(imp) location of CN XII nucleus
very medial in middle of medulla
(imp but not on exam) fcts of oculomotor n. (III)
- motor (eyes)
- autonomic (PSS for pupils)
(imp but not on exam) fcts of trochlear n. (IV)
motor
(imp but not on exam) fcts of trigeminal n. (V)
- motor
- sensory
(imp but not on exam) fcts of abducens n. (VI)
motor
(imp but not on exam) fcts of facial n. (VII)
- motor
- sensory
- autonomic
- special sensory (taste)
(imp but not on exam) fct of vestibulocochlear (VIII)
special sensory (balance and hearing)
(imp but not on exam) fct of glossopharyngeal n. (IX)
- motor
- sensory
- autonomic
- special sensory fct (taste + carotid body and sinus)
(imp but not on exam) fct of vagus n.
- motor
- sensory
- autonomic
- special sensory fct (aorta stretch + chemoRs)
(imp but not on exam) spinal accessory n. fct
motor
(imp but not on exam) hypoglossal n. fct
motor
only CN exiting dorsally
CN IV (trochlear)
how to think of CNs anatomy of hte bedside
- I: base of the frontal skull
- II: occipital (in the back). visualize optic nerves and pathways
- III, IV, VI: travel FORWARD from brainstem to eye and muscles of the eye
- V: three divisions reaching the face, each exit skull at diff place. V3 doesn’t go through cavernous sinus
- VII: UMN vs LMN
- VIII: CP angle (Cerebello-pontine angle)
- VII and VIII together travel LATERALLY
- IX and X: gag reflex
- XI: jugular foramen (where IX and X pass with it)
- XII: tongue
supranuclear lesion def
causes apparent dysfct of a cranial nerve but is actually due to damage involving fibers to or from higher brain centres (UMN lesion = supranuclear)
nuclear lesion def
involves the cranial n. itself (LMN = nuclear problem)
UMNs and LMNs in cranial n.
motor cranial nerve nuclei (the LMNs in them) are inn. by UMNs from the cortex, just like a LMN (anterior horn cell) in the spinal cord would be
sides that cranial n. innervate as a general rule
ALWAYS ipsilateral except CN IV (trochlear) = contralateral
same thing in the body, LMNs coming out of anterior horn are never crossed
UMNs crossing for cranial n.
for cranial n, UMN inn. to a cranial n. nucleus can be crossed or uncrossed. (note: UMN to an anterior horn cell (LMN) is crossed)
only have to know that for VII (facial n.) there is both ipsilateral and contralateral UMNs to the LMNs in the facial motor nuclei (the motor nuclei that belong to VII)
what to remember about each cranial n. at the bedside (for CN I to VI)
- olfactory = cribiform plate
- optic = 4 things to examine (fundi, acuity, field, pupils)
- oculomotor = LR6SO4 (lateral rectus by CN VI, superior oblique by CN IV, 4 other eye muscles by CN III)
- trochlear n. = stairs, reading
- trigeminal n. = corneal reflex
- abducens n. = false-localizing sign (so long and thin that anything with high ICP damages it)
what to remember about each cranial n. at the bedside (for CN VII to XII)
- facial n. = UMN (forehead spared, contralat muscles weak) vs LMN (forehead affected, ipsilateral muscles weak)
- vestibulocochlear = cerebello-pontine angle pathologies (CP angle)
- glossopharyngeal = gag reflex
- vagus = recurrent laryngeal n. (neck dissections)
- spinal accessory n. (jugular foramen, where glosso and vagus also travel)
- hypoglossal n. = look at the tongue
