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25 Cards in this Set
- Front
- Back
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What are the 5 types of voluntary conjugate eye movements?
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1. Smooth Pursuit
2. Optokinetic 3. Vestibular 4. Saccades 5. Vergence |
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What are the 3 ways that eye MN's are different that spinal MN's?
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1. Smallest innervation ratio in the body (lot of neurons to not many muscle fibers)
2. No stretch reflex (bc load is always the same) 3. Very fast twitch time |
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Where is the abducens nucleus located (vertically)?
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Ponto-medullary junction
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Where is the trochlear nucleus located?
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Medulla --> under the inferior colliculus
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Where is the occulomotor nucleus located?
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Beneath the superior colliculus
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What is the normal encoding of a saccade?
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Pulse + Step
Burst of spikes everytime eye moves + tonic firing to maintain position |
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The pulse generator for horizontal eye movements is located where?
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Paramedian Pontine Reticular Formation (PPRF) - near abducens nucleus
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What higher structures control the PPRF and what are their functions?
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Superior Colloculus - generates reflexive eye movements
Frontal Eye Fields - Generates conscious eye movements |
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The PPRF sends inputs to what 2 areas and what are their functions?
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1. CN VI nucleus - Creates Pulse Burst
2. Integrator - Creates tonic step |
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What is the mechanism for conjugate eye movements?
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Half of the CN VI neurons actually go through MLF and innervate CN III nucleus for MEDIAL rectus of opposite eye
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What is the general structrure of the HC units of the vestibular system?
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Kinocilia inside a cupula
Cupula in an apulla (surrounded by endolymphatic fluid) All inside semicircular canals |
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Does linear acceleration produce a net signal?
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NO
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If a head is rotating to the right, which side will increase its discharge rate?
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The right (toward where head is rotating)
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The vestibular system is designed to work extremely fast or slow?
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FAST
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What is the purpose of the Vestibular Ocular Reflex?
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Provides stability of gaze in spite of head movements
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Draw out the VOR pathway
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See 3E-19
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How is a Nystagmus named?
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For the direction of its FAST phase
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In a spontaneous nystagmus, what is usually lesioned?
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CN VIII - other CN VIII continues to fire causing the inbalance
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If the fast phase is directed to the right, where is the lesion in a spontaneous nystagmus?
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LEFT - AWAY from the lesion
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What is a calor nystagmus test?
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Put cold/warm water in patients ear and observe nystagmus?
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Cold water should give a nystagmus with what fast phase direction?
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OPPOSITE side
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Warm water should give a nystagmus with what fast phase direction?
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Same Side
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What is the gain defined as for VOR?
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Output (eye movement) / Input (head movement)
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What does the gain usually equal?
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-1
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What is very important in modifying the VOR?
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FN lobe of the cerebellum
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