CNs Flashcards
axon type, origin and termination of CN I
special sensory afferent; origin in olfactory epithelium; termination in olfactory bulb
dendrite of olfactory receptor ends in ____, from which 10-30 cilia spread over surface in a layer of mucus secreted by ____
olfactory vesicle; Bowman’s glands
axons from olfactory receptors collect into a series of bundles called ____; pass through holes in ____ of ethmoid bone
olfactory fila; cribriform plate
as the olfactory tract approaches the brain, it sends off 3 branches:
lateral olfactory stria to lateral (primary) olfactory area
intermediate olfactory stria- rudimentary in humans
medial olfactory stria to secondary olfactory area
lateral (primary) olfactory area is:
cortex over uncus, entorhinal area, limen insula, and amygdala
lateral (primary) olfactory area sends axons to ____ area which includes the uncus, entorhinal area, and limen insula
pyriform a
medial olfactory stria sends axons to:
subcallosal region of medial frontal lobe surface; emotional response to smell
olfactory bulb projections from the lateral olfactory stria
- cortex near lateral olfactory tract aka piriform area
- cortex covering amygdala aka periamygdaloid cortex
- small part of parahippocampal gyrus
- amygdala
- entorhinal area
olfactory information sent to:
thalamus, hypothalamus, hippocampus, orbital cortex, amygdala
olfactory association cortex:
orbital surface of frontal lobe and anterior insula (near taste)
axon type, origin, and termination of CN II
special sensory afferent
origin: retinal ganglion cells
termination: lateral geniculate nucleus (in thalamus), superior colliculus, hypothalamus
____ and ___ focus image on the retina
cornea; lens
focus requires ____ of light
refraction
accounts for about a third of the eyes refractive power; has major role in adjusting focus for near/far objects
the lens
most refraction is in the _____
air-water interface at the corneal surface
affects brightness and quality of image focused on the retina
iris
highly specialized cells with different structural regions
rods and cones (photoreceptors)
outer segment contains visual ____
protein/pigment
damage anterior to chiasm only affects _____ eye
ipsilateral
damage at chiasm causes _____ deficits
heteronymous
damage to optic tract causes ____ deficits
homonymous
CN III axon type, origin, termination
general somatic efferent from oculomotor nucleus to superior/inferior/medial rectus mm, inferior oblique m, and levator palpebrae superioris m.
general visceral efferent from EW nucleus to ciliary ganglion to sphincter pupillae m. (parasympathetics to the eye)
CN IV axon type, origin, termination
general somatic efferent from trochlear nucleus to superior oblique m.
CN VI axon type, origin, termination
general somatic efferent from abducens nucleus to lateral rectus m.
oculomotor nucleus is in the _____
rostral midbrain
trochlear nucleus is in the _____
caudal midbrain
abducens nucleus is in the _____
floor of the 4th ventricle, caudal pons
the near response (what happens to the eye during near vision)
ciliary muscle contracts, relaxing lens suspensory ligament and lens bulges of thickens; sphincter pupillae contracts, decreasing light coming through lens periphery (which is thinner)
accommodation for the near response involves:
constriction of the pupil, changing shape of the lens, and medial convergence of the eyes
all steps of accommodation for the near response is carried out by ____
CN III
results of CN III injury
- affected eye (ipsilateral to lesion) is “down and out”
- pt will experience diplopia or double vision
- cannot move eye medially (bc medial rectus is impaired)
- pt will experience ptosis or a drooping upper eyelid
- mydriasis- pupil on affected side is dilated
- pupil does not constrict in response to light
- lens cannot be focused for near vision
CN IV innervates ____ m.
superior oblique
results of CN IV injury
- eye tilts up slightly (pt may tilt their head to the opposite side of the defective eye to accomodate)
- pts report diplopia when going down stairs or reading
CN VI innervates ____, which abducts the eye
ipsilateral lateral rectus m.
CN VI has a long intracranial course, making it susceptible to increase ____ which usually results in _____
intracranial pressure; bilateral VI palsy
CN VI injury results in:
medial stabismus (affected eye deviates medially)
allows coordination of head and eye movement; interconnects CNs III, IV, and VI nuclei to allow this
medial longitudinal fasciculus (MLF)
CN III, IV, and VI nuclei contain ____ and ____ that ascend in MLF
motor neurons; internuclear neurons
CN VI nuclear damage causes ____ and _____
medial stabismus; lateral gaze paralysis
what happens with lateral gaze to the ipsilateral side of the lesion when CN VI nucleus is damaged
ipsilateral eye cannot abduct past midposition and contralateral eye cannot adduct past midposition
MLF injury results in:
- internuclear ophthalmoplegia
- removes excitatory input to ipsilateral CN III nucleus
- eye ipsilateral to lesion fails to look past midposition during horizontal gaze
- both VI nuclei intact so lateral movements of both eyes is intact
eyes move from one visual target to another in high-speed movement known as saccades
scanning
scanning gaze centers are in brainstem _____
reticular formation
where are the horizontal saccades
paramedian pontine reticular formation (PPRF); each pulls eye to its own side
where are the upward saccades
midbrain, rostral interstitial nuclei of the MLF (riMLF)
where are the downward saccades
in midbrain next to upward center
steps to voluntary saccade to the left
- projection from right frontal eye field activates left PPRF
- some PPRF neurons activate adjacent CN VI neurons (innervates left lateral rectus m)
- other PPRF neurons send heavily myelinated (fast) internuclear fibers in MLF to activate CN III, serving the right medial rectus
- simultaneous contraction of the respective rectus muscles yields a saccade to the left
