Cranial Nerves B&B Flashcards
how does the olfactory nerve (CN I) enter the skull, and where does it synapse?
enters via cribriform plate of ethmoid bone
synapses in olfactory bulb and travels to piriform cortex
only sense that does not relay through thalamus !
where does the optic nerve (CN II) enter the brain?
enters via optic canal of the sphenoid bone
not really peripheral nerve, arises from diencephalon
which cranial nerve arises from the diencephalon?
optic (CN II) - not technically a peripheral nerve
which 2 cranial nerves are found outside the brainstem?
olfactory (CN I) and optic (CN II)
which muscles (4) are supplied by the oculomotor nerve (CN III), and what are their actions?
- superior rectus - up
- medial rectus - medial
- inferior rectus - down
- inferior oblique - superior rotation
therefore, lesion (palsy) —> eye is down and out
[recall trochlear/CN IV supplies superior oblique for down/in]
name the 3 functions of the cranial nerve 3 (oculomotor nerve)
- moves eye (superior rectus, medial rectus, inferior rectus, inferior oblique)
- elevates eyelid (levator palpebrae)
- constricts pupil (sphincter papillae)
how does a palsy of the oculomotor nerve (CN III) present? (3)
- moves eye (superior rectus, medial rectus, inferior rectus, inferior oblique)
- elevates eyelid (levator palpebrae)
- constricts pupil (sphincter papillae)
lesion/palsy —> eye is down/out, pupil is dilated, ptosis
what is the smallest cranial nerve, and what is its function?
trochlear (CN IV): supplies superior oblique of eye, which turns eye down and in (reading, walking down stairs)
therefore, palsy —> diplopia (double vision)
name the muscles of the eye and their nervous innervation
oculomotor (CN III) —> superior rectus, medial rectus, inferior rectus, inferior oblique (superior rotation)
trochlear (CN IV) —> superior oblique (inferior rotation)
abducens (CN VI) —> lateral rectus
how does a palsy of CN IV present?
trochlear nerve: supplies superior oblique (inferior rotation of eye)
palsy —> diplopia + eye tilted outward (causes patient to tilt their head AWAY from affected side to compensate)
reading, going down stairs is difficult
eye is down/out, pupil is dilated, ptosis
where is the lesion?
oculomotor nerve (CN III)
- moves eye (superior rectus, medial rectus, inferior rectus, inferior oblique)
- elevates eyelid (levator palpebrae)
- constricts pupil (sphincter papillae)
diplopia + eye tilted outward (causes patient to tilt their head AWAY from affected side to compensate)
reading, going down stairs is difficult
where is the lesion?
trochlear nerve (CN IV): supplies superior oblique (inferior rotation of eye)
what is the key function of the trigeminal nerve (CN V)? name the 3 divisions
sensory + motor, 3 divisions: ophthalmic (V1), maxillary (V2), mandibular (V3)
key function: sensory to face (touch, pain, temp)
also part of corneal reflex (V1) and mastication (chewing)
which division of the trigeminal nerve (CN V) is part of the corneal reflex?
sensory + motor, 3 divisions: ophthalmic (V1), maxillary (V2), mandibular (V3)
ophthalmic (V1) division is part of corneal reflex - senses something touching cornea, transmits bilaterally to CN VII (facial), which causes both eyes to blink
how does palsy of CN V (trigeminal) present? (3)
mixed nerve, main function is sensory to face, also mastication
palsy —>
1. numb face
2. weak jaw - deviates towards affected side due to unopposed action of normal side
3. trigeminal neuralgia - recurrent sharp pains to half of face (rx = carbamazepine, seizure med)
Pt presents with numbness and recurrent, sharp pains to half their face, on the L side. The jaw is noted to deviate towards the left.
Where is the lesion, and what can you prescribe for the facial pain?
trigeminal (CN V) lesion - gives sensory innervation to face + mastication
jaw deviates towards lesion due to unopposed action of other side
treat tic douloureux (painful tic) with carbamazepine (seizure med, found to help here)
how does palsy of CN VI present?
abducens nerve: innervates lateral rectus, which moves eye out
palsy —> diplopia, can’t move affected eye laterally
diplopia + can’t move eye laterally
where is the lesion?
abducens nerve: innervates lateral rectus, which moves eye out
describe the functions of the facial nerve (CN VII) (3)
mixed nerve, innervates
1. muscles of facial expression [recall CN V is sensory to face]
2. taste, salivation, lacrimation
3. some ear muscles (stapedius)
explain when facial nerve (CN VII) damage affects the whole half of the face vs just the lower half
lower motor (LMN) damage causes facial droop of the whole half of face
upper motor (UMN) damage (such as MCA stroke) only causes facial droop of the lower half of the face, due to dual innervation of the upper half by both sides of the brain to the facial motor nucleus in the pons
how does palsy of facial nerve (CN VII) present? (3)
- loss of corneal reflex (motor part innervated by CN VII)
- loss of taste to anterior 2/3 of tongue
- hyperacusis (aka stapedius paralysis) - patient unable to tolerate sounds (too loud)
loss of corneal reflex + loss of taste to anterior 2/3 tongue + hyperacusis =
facial nerve (CN VII) palsy
mixed nerve, innervates
1. muscles of facial expression [recall CN V is sensory to face]
2. taste, salivation, lacrimation
3. some ear muscles (stapedius)
what is the cause of Bell’s Palsy, and how does it present?
idiopathic mononeuropathy of CN VII (facial), thought to be due to HSV-1
resolves weeks-months
what are 4 possible causes of mononeuropathy of CN VII (facial)
aka isolated palsy of CN VII
- Bell’s Palsy - idiopathic, maybe due to HSV-1
- Lyme’s disease
- tumor
- stroke (MCA)
what are the 2 portions of CN VIII and their respective functions?
vestibulocochlear nerve: sensory only
vestibular portion: compensatory eye movements, lesions cause vertigo/nystagmus/disequilibrium
cochlear portion: hearing, lesions cause tinnitus/hearing loss
how can you test CN VIII (vestibulocochlear) in an awake patient?
ask patient to focus eyes on object while you rotate their head - eyes should stay fixed on object (both CN VIII working)
if eyes rotate with the head (“doll’s eyes”), there is a CN VIII lesion - when head rotates towards lesion side, eyes move with head then quickly adjust when the head stops moving (saccade)
how can cold vs warm water be used to test CN VIII (vestibulocochlear) in an unconscious patient?
cold water is inhibitory to CN VIII - if injected in ear, eyes should slowly move towards that side, then rapidly correct to opposite side (normal = slow towards, fast away)… if CN VIII is lesioned, there is no slow movement towards cold water; but if cortex lesioned, there is no fast away
warm water is stimulating to CN VIII - if injected in ear, eyes should slowly move away from that side, then rapidly correct back towards water (normal = slow away, fast towards)… if CN VIII is lesioned, there is no slow away; but if cortex is lesioned, there is no fast towards
COWS = Cold Opposite, Warm Same (named for side of fast correction)… however, easier to just remember that if warm or cold water in ear yields no eye response, then there is a lesion on that side
which 2 cranial nerves innervate taste sensation in the tongue?
facial nerve (CN VII): anterior 2/3
glossopharyngeal (CN IX): posterior 1/3
what are the functions of the glossopharyngeal nerve (CN IX)? (5)
mixed nerve:
1. taste of posterior 1/3 tongue
2. assists in swallowing (mostly vagus)
3. salivation (parotid gland)
4. receives input from chemo- and baroreceptors of carotid body and sinus
5. stylopharyngeus (elevates pharynx)
which cranial nerve receives input from chemo- and baroreceptors of carotid body and sinus?
glossopharyngeal (CN IX)
how would glossopharyngeal (CN IX) palsy present? (4)
- loss of gag reflex (assists in swallowing)
- loss of taste posterior 1/3 tongue
- loss of sensation in upper pharynx/tonsils (innervates stylopharyngeus)
- increased HR/BP, vasoconstriction (receives carotid body/sinus input)
Pt presents with complaint of easily choking, some lack of taste, and loss of feeling in “the back of their throat.” PE is notable for elevated HR and BP. Where is the lesion?
glossopharyngeal (CN IX) palsy
- loss of gag reflex (assists in swallowing)
- loss of taste posterior 1/3 tongue
- loss of sensation in upper pharynx/tonsils (innervates stylopharyngeus)
- increased HR/BP, vasoconstriction (receives carotid body/sinus input)
what are the functions of the vagus nerve (CN X)? (7)
mixed nerve:
1. taste from epiglottis
2. swallowing
3. palate elevation
4. keeps uvula midline
5. talking
6. coughing
7. aortic arch chemo/baroreceptors
which cranial nerve receives input from the chemo- and baroreceptors of the aortic arch?
vagus (CN X) nerve
how would palsy of CN X (vagus) present?
- hoarseness, dysphasia, dysarthria (difficulty speaking)
- loss of gag reflex
- loss of sensation of pharynx and larynx
- depressed palate on affected side
- uvula deviated away from affected side
- unopposed sympathetic stimulation of the heart —> increased HR
if a patient is presenting with difficulty speaking, how can you differentiate if CN VII, CN X, or CN XII is affected?
CN VII (facial) moves muscles of face - ask the patient to say “mi mi mi,” as this requires the lips
CN X (vagus) raises the palate - ask the patient to say ”kuh kuh kuh,” as this requires elevation of the palate
CN XII (hypoglossal) moves the tongue - as the patient to say ”la, la la,” as this requires moving the tongue
state which cranial nerve is lesioned if the patient has difficulty saying any of the following:
a. “mi, mi, mi”
b. “kuh, kuh, kuh”
c. “la, la, la”
CN VII (facial) moves muscles of face - ask the patient to say “mi mi mi,” as this requires the lips
CN X (vagus) raises the palate - ask the patient to say ”kuh kuh kuh,” as this requires elevation of the palate
CN XII (hypoglossal) moves the tongue - as the patient to say ”la, la la,” as this requires moving the tongue
dilated left atrium (via mitral stenosis) or aortic dissection may cause hoarseness via compression of the _____, which is a branch of _____
recurrent laryngeal nerve,, branch of the vagus (CN X)
right RL: loops around R subclavian
left RL: loops around aortic arch
ascends towards larynx in “tracheoesophageal groove” between trachea and esophagus
what occurs in vasovagal syncope?
most common cause of syncope (fainting) - something (heat, standing, pain, sight of blood) triggers vagus nerve (CN X) to increase parasympathetic outflow
heart rate and blood pressure falls —> syncope
which 2 muscles are innervated by the accessory nerve (CN XI)?
- sternocleidomastoid - head turning
- trapezius - shoulder shrugging
if a patient has a lesion of their accessory nerve (CN XI), to which side can they NOT turn their head?
innervates sternocleidomastoid (head turning) and trapezius (shoulder shrugging)
lesion/palsy —> difficulty turning head AWAY FROM LESION + shoulder droop on affected side
if a patient has a lesion of their hypoglossal (CN XII) nerve, to which side will the tongue deviate?
“licks the lesion” - deviates towards affected side
basically, both CN XII push the tongue towards the center, but if one is lesioned it loses tug-a-war (unopposed action of normal side)
which cranial nerves are required for the corneal and lacrimation reflexes?
corneal reflex - V1 of trigeminal senses touch, VII (facial) causes blinking
lacrimation (crying) - V1 of trigeminal senses irritation, VII (facial) causes tearing [reflex tears, emotional tears are a different pathway]
which cranial nerves are required for the gag reflex?
IX (glossopharyngeal) senses, X (vagus) causes gagging
which cranial nerve(s) is the jaw jerk testing?
jaw jerk - place finger on patient’s chin and tap finger, jaw should jerk upwards
V3 of trigeminal nerve (mandibular portion) is required to sense and cause jerk - this is a test of the trigeminal nerve
which cranial nerves are required for the pupillary light reflex? (shine light in one eye, both constrict)
optic (CN II) - senses light
oculomotor (CN III) - constricts pupil
describe the innervation of the tongue’s:
a. motor
b. general sensory (pain, pressure, touch, temp)
c. taste
motor: via hypoglossal (XII)
[except palatoglossus muscle which is CN X]
general sensory: via mandibular branch of trigeminal (CN V3) for anterior 2/3, via glossopharyngeal (CN IX) for posterior 1/3, via vagus (CN X) for tongue root
taste: via facial (CN VII) for anterior 2/3, via glossopharyngeal (CN IX) for posterior 1/3, via CN X for tongue root/larynx/upper esophagus
[anterior 2/3 is separated from posterior 1/3 via terminal sulcus]
which cranial nerves exit through the middle cranial fossa, and where specifically do they exit?
CN II: via optic canal
CN III (oculomotor), IV (trochlear), V1 (ophthalmic trigeminal), VI (abducens): via superior orbital fossa
V2 (maxillary trigeminal): via foramen rotundum
V3 (mandibular trigeminal): via foramen ovale
which cranial nerves exit the skull via the superior orbital fossa?
CN III (oculomotor), IV (trochlear), V1 (ophthalmic trigeminal), VI (abducens): via superior orbital fossa
all innervate muscles of eye, except V1 which is sensation for corneal reflex
what is the only cranial nerve to exit the skull in the anterior cranial fossa?
CN I (olfactory) - exits via cribriform plate
which cranial nerves exit the skull in the posterior cranial fossa, and specifically where do they exit?
CN VII (facial), VIII (vestibulocochlear): via internal auditory meatus
CN IX (glossopharyngeal), X (vagus), XI (accessory): via jugular foramen
CN XI (accessory): also exits via foramen magnum (with brainstem)
CN XII (hypoglossal): via hypoglossal canal
name the cranial ganglia for the following parasympathetic cranial nerves:
a. CN III (oculomotor)
b. CN VII (facial) - 2
c. CN IX (glossopharyngeal)
a. CN III (oculomotor) —> ciliary ganglion
b. CN VII (facial) —> pterygopalatine (lacrimal/salivary) and submandibular ganglion (salivary only)
c. CN IX (glossopharyngeal) —> otic ganglion
