Lecture 12 - Vestibular System - Peripheral Transduction and Central Pathways Flashcards
What are the two labyrinths in the inner ear that contain the five vestibular organs (two otolith organs and three semicircular canals) of the inner ear?
bony labyrinth
membranous labyrinth
What does the bony labyrinth do?
-it is part of the temporal bond and it contains perilymph fluid and the perilymph fluid suspends the membranous labyrinth
-has the three semicircular canals
What does the membranous labyrinth do?
-within the bony labyrinth and contains the endolymph fluid which is potassium rich
-has the two otolith organs the utricle and saccule
What are the two otolith organs and what do they do?
-utricle and saccule
-detect horizontal and vertical movement of the head and body
What type of movement does the utricle detect?
detects horizontal movement of the head and body
What type of movement does the saccule detect?
detects vertical movement of the head and body
What are otoconia and where are they located?
ear crystals that are layers on top of the otolithic membrane and their added and and movement drags the otolithic membrane which in tuns bends the stereocilia of the hair cells
What are the semicircular canals how many are there and what do they do?
-there are three and are oriented 90 degrees to each other and detect rotation in three directions
What are the three directions of rotation the three semicircular canals detect?
roll - x-axis rotation - nodding your head side to side
pitch - y-axis rotation - nodding you head yes
yaw- z-axis rotation - nodding your hear no
What is located within each semicircular canal?
ampulla - a swelling
What is located within each ampulla?
-crista ampullaris which contains cupula
What does movement of the endolymph fluid cause to move in the semicircular canals?
within the ampulla there is the crista ampullaris which contains the cupula which is what moves and bends the stereocilia of hair cells
What is a type 1 hair cell?
more modern in their evolution and they have a kinocilium that modulates the sensitivity of the cell and the afferent ending which is the calyx ending which is cup shaped
What is a type 2 hair cell?
evolutionarily older has a kinocilium and many stereocilia
`What are the steps in vestibular transduction?
- movement of the endolymph fluid in the membranous labyrinth in repsone to head and body movements causes the otolithic membrane in the utricile and saccule and the cupula in the semicircular canals to move
- the stereocilia and kinocilium bend which opens the tension gated K+ channels which cause depolarization
- influx of potassium causes release of neurotransmitters to stimulate the vestibular nerve
What is the key difference between auditory and vestibular transduction?
-the direction of the fluid matters because in the vestibular the direction can cause the channels to open or close while in auditory any sort of movement of the fluid will cause the channels to open
What is the overview of the central vestibular pathway?
vestibular nerve —> vestibular nuclei in medulla and pons —-> cranial nerve nuclei for CN III, IV, and VI which is the oculomotor nerve , trochlear nerve, and abducens nerve and this coordinate eye movement with balance
What are the two descending vestibulospinal tracts and what do they do?
-communicate with muscles in the periphery to maintain balance
-medial vestibulospinal tract
- controls the medial muscle and the intercostals
-lateral vestibulospinal tract
- controls the lateral muscles in the arms and legs
What is the vestibulocerebellar circuitry?
vestibular nerve —-> vestiubular nucleus —–> flocculonodular lobe/vermis —–> fastigial nucleus —–> gaze centers, vestibular nucelus, reticular nucleus
fastigial nucleus coordinate eye movements and motor movement for balance
What is vertigo?
characterized by dizziness and nausea due to irritation of the vestibular nerve
What is Meniere’s Disease?
rare disease caused by buildup of endolymph fluid which leads to swelling in the vestibular and cochlear structures
-causing vertigo and tinnitus
