Neuro Exam 4.9
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If you damage a CN, all effects are:
Damage R CN (peripheral N), then you lose all that function on which side?
What happens if the motor and sensory nuclei associated with the CN's in the brainstem are damaged?
the same clinical results will occur
Which CN is the olfactory n?
What helps CN I decussate?
What happens if CN I is damaged?
Does anosomia occur with a unilateral lesion to CN I?
no, there is a bilateral projection pattern so you can still smell
Damage to one side of CN I causes:
loss in one nostril
can't smell out of one nostril
Which CN is the optic N?
What occurs with damage to CN II?
- loss of R and L visual fields
- occurs w/ damage to ipsilateral optic N
L visual field will be perceived in:
R occipital lobe and vice versa
If you cut L optic tract then you will no longer be able to:
see the R visual field
When does loss of R visual field due to L optic tract lesion occur?
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
Which CN is the oculomotor n?
Where are the cell bodies of CN III?
Edinger-Westphal nucleus and oculomotor nuclear complex in midbrain
What occurs with damage to CN III?
- flaccidity of ipsilateral extrinsic eye mm and levator palpebrae superioris
- from damage to nerve or occulomotor neucleus
What are the physical signs of CN III damage?
- abduction of eye
- unresponsive of pupillary light reflexes
drooping of upper eye lid due to dysfunction of levator palpebrae superioris
- 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)
Diplopia happens with damage to:
Which CNs can cause diplopia?
CN III, IV, VI
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
- eyes are crossed and not synchronized during movement
- extrinsic eye mm not properly innervated
- eye mm damaged
Which CN damage can cause diplopia?
CN III, VI
- dilated pupil
- loss of preganglionic parasympathetic fibers in N
- lack of parasympathetic input to iris (can't constrict) --Edinger-Westphal nucleus
pupils of unequal size; due to 1 iris being innervated and one not due to loss of preganglionic parasympathetic fibers of affected N
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
What is the afferent input to the iris/pupil?
What does light cause the iris to do?
Light->CN II->Edinger-Westphal nucleus (midbrain)->neuron->
If something is going wrong with pupillary light reflex what is usually the problem?
one eye reflexes w/ light shined into it
What does it mean if there is no direct reflex?
problems w/ CN II (sensory) or III (motor)
both eyes reflex w/ light in one of the eyes
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
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
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
What does a reflex diagnosis tell you?
which part of the brainstem you are dealing with
Which CN is the trochlear N?
What occurs with damage to CN IV?
CN IV LMN paralysis:
superior oblique extrinsic eye m
Diplopia (CN IV):
pt may tilt head toward shoulder of side opposite paralyzed m in order to compensate for double vision
Is strabismus included in CN IV damage?
no, b/c other occulant nn compensate
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