Physiology 3120 Lecture Notes - Lecture 8: Reticular Formation, Smooth Pursuit, Saccade

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Hore Lecture 8
-vestibular system is adjacent to auditory system
-vestibular system consists of hair cells inside membranous tubules filled with fluid
-vestibular system has two functions: record position and movement of head in space
-we never consciously think about the function of the vestibular system
-we are conscious of it only in abnormal situations when get symptoms of dizzy, nauseous or
get vertigo (think the world is turning round and round)
-three semi circular canals are made up of hair cells in fluid filled space in different planes
-records angular motion
-one semi circular canal filled with fluid called endolymph
-cupula consists of hair cells and the hair cells are embedded in a gelatinous wedge
-endolymph has mass and inertia so when head turns counter clockwise, the endolymph due to
inertia gets left behind and wrt to the head will move clockwise
-endolymph pushes on cupula which causes the hair cells to bend to signal rotational
acceleration
-also have otolith organs(utricle and saccule) that consists of hair cells and otoliths in different
orientations – in utricle have otoliths lying horizontally and in saccule have otolith lying
vertically
-otolith organs have hair cells with hairs attached to gelatinous substance containing calcium
carbonate crystals which are called otoconia or otoliths
-calcium carbonate crystals add inertia to cause different effects depending on what position
the head is in
-otolith system signals linear acceleration so horizontal or vertical acceleration
-KEY is acceleration so if have constant angular velocity, endolymph catches up with head and
no bending
-if have constant linear velocity, otoliths catch up with head and no bending
-benign positional vertigo is not uncommon
-when head whips in car accident, otoliths detach from otolith organs and get into endolymph
space which distorts its function
-leads to abnormal hair cell bending to get constant feeling of nausea and dizziness when turn
head
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