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If you damage a CN, all effects are:
ipsilateral
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Damage R CN (peripheral N), then you lose all that function on which side?
R side
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What happens if the motor and sensory nuclei associated with the CN's in the brainstem are damaged?
the same clinical results will occur
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Which CN is the olfactory n?
CN I
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What helps CN I decussate?
anterior commissure
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What happens if CN I is damaged?
anosomia
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Does anosomia occur with a unilateral lesion to CN I?
no, there is a bilateral projection pattern so you can still smell
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Damage to one side of CN I causes:
loss in one nostril
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Amnesia:
can't smell out of one nostril
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Which CN is the optic N?
CN II
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What occurs with damage to CN II?
blindness
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blindness:
- loss of R and L visual fields
- occurs w/ damage to ipsilateral optic N
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L visual field will be perceived in:
R occipital lobe and vice versa
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If you cut L optic tract then you will no longer be able to:
see the R visual field
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When does loss of R visual field due to L optic tract lesion occur?
stroke victims
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If you cut R optic N, then you will be:
- blind in R eye; but you could still see straight
- Brain still gets info from both fields b/c you L eye will have both fields
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Which CN is the oculomotor n?
CN III
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Where are the cell bodies of CN III?
Edinger-Westphal nucleus and oculomotor nuclear complex in midbrain
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What occurs with damage to CN III?
LMN paralysis
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LMN paralysis:
- flaccidity of ipsilateral extrinsic eye mm and levator palpebrae superioris
- from damage to nerve or occulomotor neucleus
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What are the physical signs of CN III damage?
- ptosis
- diplopia
- abduction of eye
- strabismus
- mydriasis
- unresponsive of pupillary light reflexes
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ptosis:
drooping of upper eye lid due to dysfunction of levator palpebrae superioris
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diplopia:
- double vision; occurs when extrinsic eye mm are paralyzed
- eyes are no longer coordinated in vertical and horizontal axes (resolves w/ time bc brain makes adjustments)
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Diplopia happens with damage to:
midbrain
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Which CNs can cause diplopia?
CN III, IV, VI
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Abduction of eye:
- laterally away from nose
- inability of eye to move medially, upward, and downward (lateral rectus --innervated by CN III-- and superior oblique are unopposed by medial rectus)
- medial rectus isn't keeping eye in midline, CN III isn't innervated well or at all
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strabismus:
- eyes are crossed and not synchronized during movement
- extrinsic eye mm not properly innervated
- eye mm damaged
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Which CN damage can cause diplopia?
CN III, VI
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mydriasis:
- dilated pupil
- loss of preganglionic parasympathetic fibers in N
- lack of parasympathetic input to iris (can't constrict) --Edinger-Westphal nucleus
- anisocoria
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Anisocoria:
pupils of unequal size; due to 1 iris being innervated and one not due to loss of preganglionic parasympathetic fibers of affected N
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Unresponsiveness of pupillary light reflexes:
- loss of preganglionic parasympathetic fibers in N w/ resultant loss of innervation of iris which controls pupil size
- pupils are just space, not a structure
- iris is contractile structure around it
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What is the afferent input to the iris/pupil?
light
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What does light cause the iris to do?
constrict
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Light->CN II->Edinger-Westphal nucleus (midbrain)->neuron->
iris
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If something is going wrong with pupillary light reflex what is usually the problem?
midbrain
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Direct reflex:
one eye reflexes w/ light shined into it
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What does it mean if there is no direct reflex?
problems w/ CN II (sensory) or III (motor)
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Consensus reflex:
both eyes reflex w/ light in one of the eyes
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How does the consensus reflex work?
collateral of CN II goes to Edinger-Westphal nuclei of opposite eye then goes to CN III of that eye and causes it to reflex --CN II talks to both eyes
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Shine light in R eye and don't get a direct reflex in R eye but get consensus reflex in L eye:
- CN II of R eye is intact and sending sensory info
- assume R CN III (occulomotor) is not working b/c that one causes the R pupil to constrict
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Shine a light in R eye and don't get direct or consensus reflex:
R CN II (optic) is not working --no afferent sensory info
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What does a reflex diagnosis tell you?
which part of the brainstem you are dealing with
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Which CN is the trochlear N?
CN IV
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What occurs with damage to CN IV?
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CN IV LMN paralysis:
superior oblique extrinsic eye m
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Diplopia (CN IV):
pt may tilt head toward shoulder of side opposite paralyzed m in order to compensate for double vision
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Is strabismus included in CN IV damage?
no, b/c other occulant nn compensate
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