Cranial Nerves Flashcards
where are the cell bodies of the olfactory nerve (cranial nerve I)?
embedded in epithelium in upper portion of nasal cavity (mucosal lining)- respond to odorants dissolved in mucus
where do the axons of the olfactory neurons (making up cranial nerve I) project through
cribriform plate of ethmoid bone, synapse on olfactory bulb (extension of CNS) mitral cells
on what cells do olfactory neurons synapse on
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)
what is the result of a single sided and bilateral olfactory neuron lesion, respectively? (give the term)
single sided = dysosmia
bilateral = anosmia (complete loss of smell)
are olfactory neurons part of the CNS?
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
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
TRUE
besides dys- or anosmia, patients with fracture of cribriform plate (where axons of cranial nerve I pass through) will also likely present with
CSF rhinorrhea
“clear sticky fluid” aka cerebrospinal fluid
is cranial nerve II a nerve
no! the optic nerve is actually a tract of the brain completley surrounded by the same meningeal coverings as everywhere else in CNS
these two cranial nerves are part of outgrowths of the CNS in some way
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)
what is the only cranial nerve affected by MS (multiple sclerosis)
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
anopsia is rare, but caused by what lesion?
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)
optic nerve (cranial nerve II) provides sensory limb of one of our cranial nerve reflexes known as ___
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)
where do the axons of the vestibular cochlear nerve (cranial nerve VIII) enter?
pons medulla junction
the semicircular canals and the utricular and saccular macula give sensory information to what cranial nerve
cranial nerve VIII, vestibulocochlear, to its vestibular component
semicircular canals maintain eye position while head moves (angular acceleration)
what are the functions of the cochlear and vestibular portions of the cranial nerve VIII, respectively?
vestibulocochlear nerve
cochlear portion- hearing
vestibular portion- balance relative to gravity (linear acceleration) and maintaining eye movement while head moves (angular acceleration)
a lesion in what cranial nerve causes sensorineural heating loss, balance problems, and vestibular evoked nystagmus
cranial nerve VIII (vestibulocochlear)
what kind of nerve is cranial nerve VIII really
vestibulocochlear
claimed to be sensory but actually mixed- enters/exits lateral portion of pons medulla junction
(efferent nerves innervate hair cells in labyrinth)
where do cranial nerves III, IV, and VI enter the orbit?
superior orbital fissure
III = oculomotor, IV = trochlear, VI = abducens
which cranial nerve innervates the levator palpebrae superioris, and what does this muscle do?
levator palpebrae superioris is innervated by cranial nerve III (oculomotor), and keeps upper eyelid up
the superior rectus, medial rectus, inferior rectus, and inferior oblique muscles are found where and innervated by which cranial nerve?
act on eyeball, innervated by CN III (oculomotor)
which of the cranial nerves innervating the eyeball contain preganglionic parasympathetic axons of the nucleus of Edinger-Westphal?
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)
where does the abducens nerve exit the midbrain (and what is its number)
CN VI, exits from caudal (lower) pons
what does the abducens nerve innervate? (hint: just one muscle)
CN VI innervates lateral rectus only
what does the trochlear nerve innervate in the eyeball (hint: just one thing)
superior oblique (CN IV)
adduct vs abduct
adduct- towards midline (medial)
abduct- away from midline (lateral)
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
what muscle of the eye utilizes a pulley system?
superior oblique
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
muscles work best when they are ____ to the ____ axis
muscles best when perpendicular to the long axis
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
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
what is the best abductor of the eye? what is best adductor?
abduction = laterally looking --> lateral rectus adduction = medially looking --> medial rectus
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!)
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)
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
what eye muscles are needed to look up? (2)
superior rectus and inferior oblique, both innervated by CN III
all eyeball elevation is controlled by CN ___
CN III
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)
what occurs if CN III is lesioned?
oculomotor- patient cannot adduct (medial) or elevate eye
what occurs if CN VI is lesioned?
abducens- patient has difficulty abducting (lateral) eye. CN VI innervates lateral rectus
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)
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)
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
