Cranial Nerves Flashcards
1
Q
where are the cell bodies of the olfactory nerve (cranial nerve I)?
A
embedded in epithelium in upper portion of nasal cavity (mucosal lining)- respond to odorants dissolved in mucus
2
Q
where do the axons of the olfactory neurons (making up cranial nerve I) project through
A
cribriform plate of ethmoid bone, synapse on olfactory bulb (extension of CNS) mitral cells
3
Q
on what cells do olfactory neurons synapse on
A
mitral cells in olfactory bulb- give rise to pair of olfactory tracts that project to other parts of CNS (olfactory bulb is extension of CNS)
4
Q
what is the result of a single sided and bilateral olfactory neuron lesion, respectively? (give the term)
A
single sided = dysosmia
bilateral = anosmia (complete loss of smell)
5
Q
are olfactory neurons part of the CNS?
A
no, the neurons are part of the peripheral nervous system since their cell bodies are in mucosal lining of nasal cavity. but they project to mitral cells in olfactory bulb, which is extension of CNS
6
Q
T/F: the olfactory bulb, as an extension of the CNS, is covered in all the same meninges, including dura, arachnoid, subarachnoid space with CSF, and pia
A
TRUE
7
Q
besides dys- or anosmia, patients with fracture of cribriform plate (where axons of cranial nerve I pass through) will also likely present with
A
CSF rhinorrhea
“clear sticky fluid” aka cerebrospinal fluid
8
Q
is cranial nerve II a nerve
A
no! the optic nerve is actually a tract of the brain completley surrounded by the same meningeal coverings as everywhere else in CNS
9
Q
these two cranial nerves are part of outgrowths of the CNS in some way
A
cranial nerve I (olfactory)- cell bodies in mucosal linings but project to mitral cells in olfactory bulb, which is extension of CNS
cranial nerve II (optic)- not a nerve but a tract of CNS (optic nerve + retina = outgrowth)
10
Q
what is the only cranial nerve affected by MS (multiple sclerosis)
A
cranial nerve II (optic)- not really a nerve but a CNS tract, so its axons are myelinated by oligodendrocytes of all tracts ascending/descending through parts of brain
MS is autoimmune destruction of oligodendrocytes
11
Q
anopsia is rare, but caused by what lesion?
A
anopsia = total loss of visual representation on affected side of eye
caused by lesion of optic nerve (cranial nerve II, really a tract of brain)
12
Q
optic nerve (cranial nerve II) provides sensory limb of one of our cranial nerve reflexes known as ___
A
pupillary light reflex- when you shine light on one eye, stimulating optic nerve, both pupils constrict
(optic nerve bilaterally activates parasympathetic axons in both ocular motor nerves)
13
Q
where do the axons of the vestibular cochlear nerve (cranial nerve VIII) enter?
A
pons medulla junction
14
Q
the semicircular canals and the utricular and saccular macula give sensory information to what cranial nerve
A
cranial nerve VIII, vestibulocochlear, to its vestibular component
semicircular canals maintain eye position while head moves (angular acceleration)
15
Q
what are the functions of the cochlear and vestibular portions of the cranial nerve VIII, respectively?
A
vestibulocochlear nerve
cochlear portion- hearing
vestibular portion- balance relative to gravity (linear acceleration) and maintaining eye movement while head moves (angular acceleration)
16
Q
a lesion in what cranial nerve causes sensorineural heating loss, balance problems, and vestibular evoked nystagmus
A
cranial nerve VIII (vestibulocochlear)
17
Q
what kind of nerve is cranial nerve VIII really
A
vestibulocochlear
claimed to be sensory but actually mixed- enters/exits lateral portion of pons medulla junction
(efferent nerves innervate hair cells in labyrinth)
18
Q
where do cranial nerves III, IV, and VI enter the orbit?
A
superior orbital fissure
III = oculomotor, IV = trochlear, VI = abducens
19
Q
which cranial nerve innervates the levator palpebrae superioris, and what does this muscle do?
A
levator palpebrae superioris is innervated by cranial nerve III (oculomotor), and keeps upper eyelid up
20
Q
the superior rectus, medial rectus, inferior rectus, and inferior oblique muscles are found where and innervated by which cranial nerve?
A
act on eyeball, innervated by CN III (oculomotor)
21
Q
which of the cranial nerves innervating the eyeball contain preganglionic parasympathetic axons of the nucleus of Edinger-Westphal?
A
CN III (oculomotor) axons of Edinger Westphal innervate smooth muscle that constricts pupil and ciliary muscle the causes reflex change in shape of lens (near response)
22
Q
where does the abducens nerve exit the midbrain (and what is its number)
A
CN VI, exits from caudal (lower) pons
23
Q
what does the abducens nerve innervate? (hint: just one muscle)
A
CN VI innervates lateral rectus only
24
Q
what does the trochlear nerve innervate in the eyeball (hint: just one thing)
A
superior oblique (CN IV)
25
adduct vs abduct
adduct- towards midline (medial)
| abduct- away from midline (lateral)
26
what directional movement of your eyeball is strictly involuntary
external or internal rotation
extorsion vs intorsion
happens when you tilt your head to maintain focus on upright object
27
what muscle of the eye utilizes a pulley system?
superior oblique
28
which muscles of the eye pull the eyeball in opposite direction of constriction?
superior and inferior oblique, because they pull on back half of eyeball
29
muscles work best when they are ____ to the ____ axis
muscles best when perpendicular to the long axis
30
in what eye position will the rectus muscles work best (think of physics of muscle contraction)
works best when the eye is slightly abducted (laterally looking) because that puts cornea in position that's directly perpendicular to long axis of rectus muscles
31
in what eye position will oblique muscles work best (think physics)
oblique muscles work best when eye is slightly adducted (medial looking) because that puts axis of eye perpendicular to contracting fibers of oblique muscles
32
what is the best abductor of the eye? what is best adductor?
```
abduction = laterally looking --> lateral rectus
adduction = medially looking --> medial rectus
```
33
match:
CN III and VI
medial rectus and lateral rectus
adduction and abduction
```
CN III (oculomotor) innervates medial rectus (adduction)
CN VI (abducens!) innervates lateral rectus (abduction!)
```
34
```
the superior oblique of the eye is innervated by:
CN III
CN IV
CN VI
CN VII
```
superior oblique is the only muscle innervated by CN IV (trochlear)
(inferior oblique controlled by CN III)
35
how can physicians use the H in space to test the superior rectus independently of the inferior oblique (both used to look up)? what about vice versa?
test superior rectus- patient abduct (medial) eye first, then look up, because superior rectus works best when eye is abducted (physics of muscles- want to be perpendicular from long axis)
test inferior oblique- adduct (medial), then up
36
what eye muscles are needed to look up? (2)
superior rectus and inferior oblique, both innervated by CN III
37
all eyeball elevation is controlled by CN ___
CN III
38
how can physician's use H in space to test the only muscle controlled by CN IV?
CN IV only controls superior oblique (pulls eye down- oblique contraction causes eye to move in opposite direction of contraction) (but is a weak abductor)
patient adducts (medial) first, then looks down. superior oblique is best depressor when eye is adducted (due to physics)
(to test inferior rectus in isolation, patient abducts then looks down)
39
what occurs if CN III is lesioned?
oculomotor- patient cannot adduct (medial) or elevate eye
40
what occurs if CN VI is lesioned?
abducens- patient has difficulty abducting (lateral) eye. CN VI innervates lateral rectus
41
what occurs in eye if CN IV is lesioned?
trochlear- patient can't look down from adducted (medial) position. CN IV innervates superior oblique (note that superior oblique works best when eye is adducted, but is itself a weak abductor)
42
besides innervating the medial/inferior/superior rectus, inferior oblique, and levator palpebrae superioris, the ocular motor nerve also carries parasympathetic input into the orbit. what does this PNS input innervate?
sphincter pupillae- constricts pupil in response to light
ciliary muscle- causes reflex change in shape of lens to accommodate depth of field (like adjusting eyes to read a book)
43
what are the 3 functions of the superior oblique muscle, innervated by the trochlear nerve (IV)?
depresses the eye, but also a weak abductor, and intorsion
44
diplopia
visual axes of eyes are misaligned, causing double vision. will occur with lesion of any ocular nerve
45
strabismus is a symptom of lesion which cranial nerves?
lesion of CN III (oculomotor) or VI (abducens) causes strabismus (squinting) because diplopia (misaligned axes of eye) is irritating
squint to hide diplopia
46
what are the symptoms of lesion of CN III
(oculomotor)
lose ability to adduct eye (loss of innervation to medial rectus) and eye is pulled away from nose due to unopposed action of lateral rectus (CN VI)--> causes diplopia with lateral strabismus
ptosis (eyelid droop) due to loss of innervation to levator palpebrae superioris
inability to constrict pupil on side of lesion--> dilated pupil from unopposed action of sympathetic input
(also weakened near response due to weak ciliary muscle)
47
external compression to CN III (such as by berry aneurysm or uncal herniation) has what effect?
loss of parasympathetic input via CN III because PNS axons of CN III run on outside of nerve
patient will present with dilated pupil
48
a patient presents with internal/medial strabismus (eye is pulled towards nose). where is the lesion likely?
```
CN VI (abducens, innervates lateral rectus)
result is unopposed action of medial rectus pulling eye towards nose
```
will also present with pseudo-ptosis because internal strabismus will cause them to squint to eliminate diplopia
49
a patient presents with difficulty reading a book or going down the stairs. the patient also tilts their head in one direction. what lesion is most likely? (hint: difficulty is due to muscles of eye)
CN IV (trochlear) lesion- innervates superior oblique (depresses eye when eye is in adducted position)
this patient will also have weakness with intorsion of the eye--> eye on affected side will be extorted, so patient will tilt head away from lesion side. when head is tilted the normal eye will intort to limit extorsion-induced diplopia
50
the sympathetic pathway uses a 3-neuron system to innervate the eye. what are they?
1. hypothalamus (autonomic sympathetic output)
2. thoracolumbar spinal cord (mainly T1)
3. superior cervical ganglion- these form a plexus on the carotid system of arteries that go to the orbit
51
a lesion of the plexus of post-ganglionic sympathetics on the internal carotid artery will result in constricted pupil and slight ptosis on the ____ side of the lesion?
superior cervical ganglion makes 3rd neuron in 3-neuron sympathetic pathway to eye, and forms plexus on carotid system of arteries
effect will be on ipsilateral side of lesion
52
parasympathetic innervation to the eye constricts the pupil via axons exiting from the nucleus of ____ in the ___ part of the midbrain?
parasympathetic innervation to the eye constricts the pupil via axons exiting from the nucleus of EDINGER-WESTPHAL in the UPPER (rostral) part of the midbrain?
the axons run with oculomotor nerve and synapse with ciliary ganglion inside orbit to generate pupillary constriction
53
how does a lesion of the facial nerve (VII) manifest in the eye?
```
facial nerve (mixed) gives ability to shut the eye (contracts orbicularis oculi muscles)
lesion results in Bell's palsy- weakness of all muscles of facial expression on ipsilateral side
```
patient can't shut eye, wrinkle forehead, flare nostrils, purse lips
54
how does lesion of trigeminal nerve manifest in eye?
trigeminal nerve (V, mixed) provides sensory innervation to cornea- blink reflex (of both eyes) is lost
55
function and location of paramedian pontine reticular formation (PPRF)?
horizontal gaze generating center
right next to abducens nucleus (CN VI) in pons
(makes sense because we need abducens for horizontal gaze)
56
function and location of rostral interstitial nucleus?
nucleus that controls vertical conjugate gaze
| found in midbrain
57
horizontal conjugate gaze is ipsilateral/contralateral? what is the term for these rapid conjugate eye movements?
contralateral- UMN on opposite side and superior colliculus on opposite side fire first (simultaneous)
generate saccadic or rapid conjugate eye movements (saccadic means both eyes move in same direction)
58
which two centers of brain are capable of generating contralateral horizontal conjugate gaze? how do they differ in function?
UMN (voluntary) and superior colliculi (reflexive)
lesion to either causes only temporary deficits in saccadic eye movements horizontally, so they must work together in a way
59
saccades
rapid, or ballistic, movements of both eyes that quickly generates horizontal gaze to locate a different visual target
60
describe how horizontal conjugate gaze is generated to the left
must abduct left eye (lateral rectus, CN VI) and adduct right eye (medial rectus, CN III)
neurons in right frontal eye field project out of cortex (UMN, contralateral), descend to innervate right superior colliculus.
both projections from superior colliculus/ UMN cross midline of brainstem, synapse on left PPRF
PPRF projects to left abducens (CN VI) which are right next to it in caudal pons (left eye has signal).
PPRF sends axons through medial longitudinal fasciculus that cross midline, project to right oculomotor in midbrain (CN III)- now right eye has signal
61
in order to generate horizontal conjugate gaze, both CN VI and III must be activated (have opposite abduct, adduct function), but the PPRF is right next to CN VI. how does signal get to CN III?
PPRF sends axons through medial longitudinal fasciculus (connects CN VI in caudal pons and CV III in midbrain)
62
the medial longitudinal fasciculus is heavily myelinated, so it is susceptible to demyelination by this disease
multiple sclerosis
(MLF must be heavily myelinated because it connects CN VI in caudal pons to CN III in midbrain for saccadic eye movement necessary for horizontal conjugate gaze)
63
internuclear ophthalmoplegia can be caused by multiple sclerosis. what is it?
MS demyelinates medial longitudinal fasciculus that connects CN VI (caudal pons) to CN III (midbrain) for horizontal conjugate gaze
internuclear ophthalmoplegia- disruption of MLF that results in inability to adduct eye on attempted horizontal conjugate gaze (CN III works, but isn't getting signal)
64
will convergence be affected by internuclear ophthalmoplegia?
no, convergence doesn't require MLF (that's for horizontal conjugate gaze)
convergence uses visual input to change depth of field from infinity to close (like reading a book)- near response
65
a patient with internuclear ophthalmoplegia will demonstrate what symptom in the normal abducting eye when attempting a saccade to either side?
monocular nystagmus- attempt by CNS to pull abducting eye back in line with eye that can't adduct (because of MLF lesion) because it doesn't like the diplopia (misaligned axes)
66
CN V (trigeminal, mixed) enters/exits from rostral pons with 3 divisions. Which division is the only one that carries LMN, innervating muscles of mastication?
mandibular division. does not go through cavernous sinus as ophthalmic and maxillary divisions do
67
what are the 3 divisions of CN V
CN V = trigeminal, mixed
1. ophthalmic (top of face)
2. maxillary (middle of face, medial aspect of external auditory meatus)
3. mandibular (bottom of face, including anterior tongue)
68
all of the cell bodies of cranial nerves are where? (simple, general answer here)
outside of brainstem
69
what are the general sensations
touch, pain, temp
70
a patient presents with complete loss of sensation on one side of their face. where is the lesion?
lesion of CN V (trigeminal, mixed) inside rostral pons- all 3 divisions are ipsilaterally affected (ophthalmic, maxillary, mandibular)
71
a patient presents with stapedius weakness, inability to flare nostrils and shut eyes, dry eye due to loss of lacrimation, and loss of taste in anterior tongue. what CN is lesioned, and where is this CN located in brain stem?
CN VII (facial, mixed), enters/exits lateral caudal pons
(parasympathetic component of CN VII innervates salivary glands, nasal and palatine mucus glands, lacrimal gland)
(sensory component responds to taste from anterior tongue)
72
touch, pain, temp sensation from anterior tongue is carried by ___
taste from anterior tongue is carried by ___
general sensation- trigeminal (V, rostral and lateral pons)
| taste- facial (VII, caudal and lateral pons)
73
patient presents with Bell's palsy and hyperacusis. where is the lesion?
Bell's palsy = loss of facial sensation
hyperacusis = hypersensitivity to loud sound
lesion in CN VII (facial, mixed)- innervates face muscles and also stapedius muscle in ear
lesion could be outside of brainstem or at caudal pons
74
what are the upper medulla cranial nerves?
IX (glossopharyngeal) and X (vagus), both mixed. enter/exit upper medulla laterally (as mixed nerves do)
75
this cranial nerve can't be functionally tested by its motor functions. it innervates a single skeletal muscle, the stylopharyngeus, and motor fiber of the parotid gland (causing secretion). it can be tested by its visceral sensory fibers, however, from mucosa of posterior tongue and oropharynx. what is? what reflex is used to test it?
CN IX (glossopharyngeal, mixed). upper medulla CN
test with gag reflex
76
what CN can be tested with gag reflex?
```
CN IX (glossopharyngeal) and X (vagus)
IX gives sensory input to motor fibers of X to initiate gag reflex
```
77
the nucleus ambiguus gives rise to which CN motor neurons?
IX (glossopharyngeal) and X (vagus)
78
which CN innervates virtually all of pharynx, larynx, and palate muscles?
X (vagus, mixed, upper medulla)
79
this CN carries parasympathetics going down to thorax and abdomen (but these are not easily evaluated clinically). what is?
X (vagus, mixed, upper medulla)
80
patient presents with drooping palate, dysphagia, deviated uvula, and hoarseness. where is the lesion?
CN X (vagus, mixed, upper medulla)
| hoarseness because of affected larynx
will also lack gag reflex on side of lesion (ipsilateral)
81
what is the doctor testing by having you say "ah"?
```
CN X (vagus, mixed, upper medulla)
palate should elevate bilaterally
```
82
which nerve is a misplaced cervical spinal cord nerve? where does it enter and exit cranial cavity?
```
CN XI (accessory, motor)
enters through foramen magnum, exits through jugular foramen
```
83
the sternocleidomastoid (in lateral part of neck, turns chin away from contracting muscle to opposite side) and trapezius are innervated by?
CN XI (accessory)
84
what CN innervates genioglossus muscle, and how is it tested?
```
CN XII (hypoglossal)- innervates muscles of tongue ("glossal")
genioglossus muscles converge to stick tongue out. lesion will cause tongue to deviate towards side of lesion ("licking the lesion")
```
85
the ___ nucleus is a visceral sensory nucleus found throughout much of the length of the medulla, sticking into the caudal pons, and receives cranial nerve input responding to taste. what is?
solitary nucleus. the rostral end of the solitary nucleus receives taste input from tongue, palate, epiglottis
86
which region of the solitary nucleus in the brain stem is gustatory
rostral end of solitary nucleus. receives taste input from CN 7 (facial), 9 (glossopharyngeal), 10 (vagus)
87
what 3 CN provide gustatory input, and where do they provide it?
CN 7 (facial), 9 (glossopharyngeal), 10 (vagus), to solitary nucleus (solitary tract in brain stem)
88
which areas of the tongue are innervated by CN 7, 9, 10?
```
CN 7 (facial)- anterior tongue and soft palate
CN 9 (glossopharyngeal)- posterior and circumvallate papillae (on anterior/posterior border)
CN X (vagus)- epiglottis
```
all of these project into solitary nucleus in brain stem (solitary tract)
89
the caudal end of the solitary nucleus responds to ___ while the rostral end responds to ____
caudal solitary nucleus- cardio/respiratory input (from carotid body and carotid sinus)
rostral solitary nucleus- taste (CN 7, 9, 10)
90
the caudal end of the solitary nucleus in the brain stem responds to cardio/respiratory input from these two receptors
carotid body- blood chemistry (near bifurcation of common carotid artery)
carotid sinus- baroreceptor (proximal part of internal carotid artery, so after bifurcation)
91
for most of sensory systems, the second neuron in processing sends axons across the midline. what is exception?
taste projection- ipsilateral
92
all taste fibers from CN 7, 9, and 10 enter the brain stem at ___ and synapse on second neurons in the solitary nucleus in the ____ part of the ____
CN 7, 9, 10 enter brain stem at upper medulla, synapse on solitary nucleus in upper/lateral medulla
93
this tract forms the "expressway" of the reticular system, carrying neurons associated with the locus coeruleus (for NE) and raphe nucleus (for ST), but it also carries the taste fibers arising from the solitary nucleus. what is?
central tegmental tract
94
taste fibers of CN 7, 9, and 10 synapse on solitary nucleus in upper/lateral medulla (2nd neuron), then take central tegmental tract up to the 3rd neuron where?
3rd neuron of taste sensory system is ventral postural medial nucleus of thalamus- sensory relay nucleus
95
what is the function of the ventral postural medial nucleus of the thalamus?
sensory relay nucleus for cranial nerve sensations
96
after travelling from the solitary nucleus to the ventral postural medial nucleus in the thalamus (via the central tegmental tract), taste fibers project to these 2 places;
postcentral gyrus (inferior part)
insular cortex (buried inside lateral fissure)- connected to prefrontal cortex, where olfactory/ gustatory/ somatic sensory info combined for complex flavor sensation
97
how many neurons are used in pathway of taste projection
1. CN 7, 9, 10
2. solitary nucleus
3. ventral postural medial nucleus in thalamus (sensory relay)--> these project to postcentral gyrus and insular cortex
98
the trigeminal nerve (V) enters at the rostral pons, at the point where the ____ sensory nucleus of CN V is
main or principal sensory nucleus
99
what are the 3 nucleus sections of CN V in the brain stem?
CN V = trigeminal
1. mesencephalic nucleus (midbrain)
2. principal/ main (only found at CN V point of entry in rostral pons)
3. spinal nucleus (extends down length of brainstem)
100
what does mesencephalic, principal/main, and spinal nucleus of CN V respond to?
mesencephalic- proprioception (muscles of mastication mostly)
principal/main- touch (anterior tongue, oral and nasal cavities)
spinal- facial pain and temperature
all contralateral sensation
101
what are the 3 divisions of the cutaneous fibers of CN V in the face?
CN V = trigeminal
| ophthalmic (V1), maxillary (V2), mandibular (V3)
102
which cutaneous fiber division of CN V gives sensory input of the cornea?
V1- ophthalmic
| CN V = trigeminal
103
the Gasserian or semilunar ganglion refer to the ganglion of what CN?
CN V, trigeminal
104
the trigeminal nerve (CN V) carries axons into the rostral pons through 2 parallel processing pathways. contrast them
one is for facial touch: heavily myelinated tactile fibers synapse with principal/main/chief sensory nucleus of CN V (found at point of entry in rostral pons)
other is for facial pain/temp: unmyelinated axons go through spinal nucleus of CN V (which stretches down bottom portion of brainstem)
either way, axons cross midline and go up to thalamus
105
the heavily myelinated fibers of facial touch coming from CN V go to the principal/chief/main sensory nucleus of CN V in the rostral pons, then coalesce with the ____ on the opposite side of the brain stem to go to the thalamus
join the medial meniscus, which is going to similar place in thalamus
medial meniscus caries touch/proprioceptor modalities from contralateral limb/trunk
both synapse on ventral postural medial subthalamic nucleus
106
what kind of input does medial meniscus carry
touch and proprioceptor modalities from contralateral limb and trunk
107
the unmyelinated CN V (trigeminal) fibers carrying pain/temp sensation go through spinal nucleus of CN V (lower part of brain stem) before ascending up with the ____ tract on the contralateral brainstem (cross midline at level of cell body)
spinothalamic tract (processing pain/temp contralaterally from limb and trunk)
both synapse on second neurons in VPM thalamus (conveys pain/temp to contralateral somatosensory cortex)
108
complete lesion of CN V (trigeminal) results in ipsilateral facial anesthesia and weakness of mastication muscles. What's different if just the fibers descending down below the CN V entry of brainstem (rostral pons)?
this would be lesion of spinal nucleus of CN V, lateral part of brainstem below point of entry of CN V
if the nucleus is lesioned- contralateral loss of just pain/temp (not touch)
if the incoming spinal tract of CN V is lesioned- ipsilateral loss of just pain/temp (not touch)
