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Name some components of the auditory and vestibular system
- semicircular canal (anterior, horizontal, and posterior)
- vestibulocochlear nerve
- utricle and saccule
- oval window
- cochlea
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What is otoconia?
- "ear rocks"
- inside utricle and sacule that can become dislodged with aging leading to idiopathic balance
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What is the purpose of the auditory system?
- orients head and eyes toward sound
- activates CNS activity levels
- conscious awareness and recognition of sounds
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What are the basic 7 steps of the auditory system to convert sound to neural signals?
- sound hits eardrum
- tympanic membrane moves the ossicles
- fluid inside the cochlea distorts
- basilar membrane moves hair cells
- hairs bends against tectoral membrane
- receptor potential generated
- CN VIII depolarizes
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Where are the 3 places that the cochlear nuclei sends input to?
- medial geniculate body
- inferior colliculus
- reticular formation
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What is the function of the reticular formation in the auditory system?
helps activate NS- arousal
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What is the function of the inferior colliculus in the auditory systme?
orients eyes/head toward sound
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What is the function of the medial geniculate body in the auditory system?
conscious recognition of sound
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What are the 3 different types of deafness and their differences?
- nerve deafness: disruption of auditory portion of CN VIII
- conduction deafness: defect of external or middle ear (tympanic membrane/vessicles)
- central deafness: damage to central connections (cochlear nuclei, lateral lemniscus, etc)
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What is the Weber test?
- strike tuning fork and place on center of head
- should sound same in both ears
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How is nerve deafness and conduction deafness decided with the Weber Test?
- nerve deafness: sound centralized in normal ear
- conduction deafness: sound centralized in affected ear
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What is Rinne Test?
strike tuning fork and hold to mastoid process and remove when sound is gone
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What are the responses for the Rinne Test?
- normal: AC > BC
- nerve deafness: AC > BC but both reduced
- conduction deafness: BC > AC
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What is the purpose of the vestibular system?
- info on movement and head position in relation to gravity
- gaze stabilization
- posture adjustment/balance
- input to autonomic and arousal systems
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What types of movements stimulate the semicircular canals?
rotational movement of the head
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What types of movements stimulate the saccule and utricle?
linear movement of the head
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Input from the vestibular nuclei and vestibulocerebullum to the cerebral cortex causes what?
perception of head orientation
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Input from the vestibular nuclei and vestibulocerebullum to the oculomotor nuclei causes what?
eye movement
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Input from the vestibular nuclei and vestibulocerebullum to the spinal cord causes what?
postural control
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What is nystagmus?
Slow saccade in 1 direction followed by rapid compensation in opposite direction
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What is nystagmus a disruption of?
vestibular nuclei of MLF
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If you have a patient look to the R and the L MLF is damaged what happens
- L eye to midline and stops
- R eye will abduct and have nystagmus
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If you have a patient look to the R and the R abducens nucleus is damaged what happens?
- L forced lateral gaze
- R eye deviates to midline (no lateral rectus)
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If you have a patient look to the R and the R abducens nerve is damaged what happens?
- R eye deviates mediallys
- L eye could have convergence response and move medially
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Does convergence move under the MLF?
no, it's under cortical control
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What are the three places the retina sends information to?
- lateral geniculate of thalmus
- tectum
- pretectal area
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Input from the retina to the lateral geniculate body does what?
- specifies how to move (visual guidance)
- visual ojectification of objects
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Input from the retina to the tectum has what function?
orientation, visually guided movements of the eye
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Input from the retina to the pretectal area has what function?
pupillary reflex
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If in L visual field, where is it recieved?
R retinal field
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If in upper visual field, where is it received?
lower retinal field
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Where does the nasal retina fields send axons to?
project to the OPPOSITE lateral geniculate body
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Where does the temporal retina field send axons to?
project to lateral geniculate body on the SAME side
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What does right optic nerve disruption causes?
blindness of R eye
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What does optic chiasm disruption cause?
- complete midline transection causing bitemporal hemianopsia
- tunnel vision
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What does right angle of chiasm disruption causes?
- R nasal hemianopsia
- tunnel vision of R eye
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What is right angle of chiasm disruption often misdiagnosed as?
torticollus
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What does disruption of the right optic tract cause?
- L homonymous hemianopsia
- abcess or tumor of temporal lobe
- temporal blocked in left eye, nasal blocked in right eye
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What does complete capsular destruction of R optic radiation cause?
- L homonymous hemianopsia
- temporal blocked in left eye, nasal blocked in right eye
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What does disruption of R Meyer loop or lower part of geniculocalcenne tract cause?
- L homonymous superior quadrantic anopsia
- top left quarter of both eyes blocked
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What does disruption of the upper part of the R geniculocalcerine tract cause>
- L homonymous inferior quadrantic anopsia
- bottom left quarter of both eyes blocked
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What does disruption of R striate area cause?
- L homonymous hemianopsia
- L half of both eyes blocked, with center not blocked?
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