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Bio 222 Exam 3
Lec 16 - Vestibular system
13
Biology
Undergraduate 4
11/16/2010

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Term
vestibular labyrinth and cochlea
Definition
organ of balance and organ of hearing
vestibular portion of cranial never VIII, auditory portion of cranial nerve VIII
-membranous sacs within both bony strucutres are filled with ENDOLYMPH=high K+ and low Na+ (similar to cytoplasm
Term
Vestibular labyrinth
Definition
consists of 2 types of structures: 2 otolith organs, 3 semicircular canals
-each structure has a sensory epithelium containing hair cells, sensory cells for movement
Term
sensory epithelium has polarized organization
Definition
-groups of hairs cells have their kinocilia oriented in the same direction
-deflection of cilia towards kinocilium causes depolarization
Term
otolith organs (function, division)
Definition
-Function: detects head tilt and linear accelerations
-sensory epithelium=macula
Utricle=macula oriented parallel to the ground, detects motion on horizontal plane
SACCULE=macula oriented perpendicular to ground, detects gravity and vertical fall
Term
semicircular canals
Definition
-Function: to detect angular accelerations (rotation)
-sensory epithelium=crista
-has 3 canals (superior, posterior, lateral)
-each canal joins the utricle at an enlargement called the AMPULLA that houses the crista and a gelatinous structure called the cupula
Term
crista orientation in semicircular canals
Definition
in the cirsta, unlike the macula, the kinocilia of ALL the hair cells are oriented in the same direction
Term
signal transduction in hair cells
Definition
stretch activated cation channels open when cilia deflected towards kinocilium
1. Ca2+ influz leads to membran depolarization
2. voltage gated Ca2+ channels open
3. neurotransmitter is released to vestibular ganglion cells
Term
structure of the macula
Definition
hair cells of macula covered by:
-a gelatinous layer (cilia embedded here)
-otolithic membrane (embedded with otoliths)
-weight of otoliths causes deflection of cilia during movement
Term
push-pull activation of horizontal semicircular canals during head rotation
Definition
TURNING LEFT
L canal:
1. increased firing during accell
2. adaptation in firing rate during constant velocity
3.decreased firing during deceleration

R canal=oppposite responses
Term
vestibular axons project to...
Definition
-cerebellum
-lateral vestibular nucleus (otolith)
-medial vestibular nucleus (semicircular)
Term
Lateral vestibular nucleus projects to...
Definition
limb motor neurons (maintain posture)
Term
medial vestibular nucleus project to..
Definition
-neck motor neurons (orient head)
-extraocular motor nucleai III, IV, VI
Term
vestibulo-ocular reflex (VOR)
Definition
-maintains focus during head motion
-direction of eye movement is opposite the direction of the head turn
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