25/ the vestibular system

Question 1

what is the vestibular system responsible for

Answer 1

• which way is up
• which way are you going
• keeps eyes still as we move
• maintain upright posture
• ability to perceive own movement within space

Question 2

main parts of vestibular system anatomy

Answer 2

• vestibular nerves
• ampulla
• semicircular canals (head rotation), set at 90 degrees from each other: anterior vertical, posterior vertical, horizontal
• otolith organs (linear motion): utricle, saccule

Question 3

what fluids are present? where is one of them, dif between fluids

Answer 3

• endolymph (high k)
• perilymph (normal)
• saccule, utricle, ampulla and semicircular canals all filled w endolymph
• perilymph around everything

Question 4

vestibular hair cells structure

Answer 4

• hair bundle w stereocilia (projections) and tip links
• kinocilium (in centre), defines polarity of hair cell by determining direction of staircase, longest projection
• stereocilia aren’t defined in obvious 3 length rows like cochlear hairs - still has staircase. works at lower frequency of movement

Question 5

mechanism of how vestibular hair cells work - mechanosensitive

Answer 5

• same principle as hairs of auditory system but at lower frequencies
• stereocilia move towards top of staircase = excitation and depolarisation, towards bottom = inhibition and hyperolarisation
• at rest = resting discharge - natural depolarisation at rest, allowing it to be turned up/down

Question 6

what frequencies does vestibular system respond to

Answer 6

0-20 Hz

Question 7

2 types of vestibular hair cell

Answer 7

• type I: had a massive dendritic terminal around while of hair cell, so v reliable transmission. called calyx
• type II: normal, dendritic terminal only around from where nt is released from

Question 8

what do the saccule and utricle detect

Answer 8

• saccule: up/down
• utricle: left/right
• head tilt and linear acceleration

Question 9

how do the saccule and utricle work

Answer 9

• gelatinous otolithic memb sits on top of hair bundles - hair bundles project into it
• on top of that is otoconia, calcium carbonate structure (like sprinkles on jelly)
• when head is moved, gravity pulls heavier otoconia down, which pulls hair bundles in a left/right direction

Question 10

what is the area vestibular hair cells are found in called

Answer 10

macula

Question 11

function and location of the striola

Answer 11

• found in the macula
• defines half way through the macula
• one one side hair bundles are rotated in one direction, other side hair bundles are rotated in the other direction

Question 12

how do we distinguish between increased firing in afferent fibres due to head tilt or linear acceleration

Answer 12

• we don’t rely on input from vestibular system alone
• inputs from visual and proprioception systems
• consciously moved

Question 13

structure of the semicircular canals

Answer 13

• cupula: gelatinous structure (softer than otolithic memb) penetrated by hair bundles
• ampulla: swelling around semicircular canal
• filled with endolymph

Question 14

how do semicircular canals detect angular acceleration

Answer 14

• inertia of endolymph during rotation displaces the cupula, which moves hair bundles in a direction - sensation of movement
• eg: if you spin to the left, endolymph moves as if to the right (its actually staying still)
• happens at start of spinning - takes longer to speed up, and longer to slow down

Question 15

how do semicircular canals work in pairs

Answer 15

• horizontal canals on both sides lie in same plane so act as a functional pair
• anterior canal lies in parallel w the posterior canal on the other side - acts as a functional pair
• when left side is activated, right is inhibited

Question 16

central pathways connected to the vestibular nerve

Answer 16

• vestibular organs feed into the cerebellum, which feeds into vestibular nuclei, and straight into vestibular nuclei
• vestibular nuclei feeds into spinal cord, oculomotor nuclei (leads to extraocular muscles - eyes movements), and reticular formation (sickness sensation when spinning), which also leads to oculomotor nuclei

Question 17

vestibulo-ocular reflex

Answer 17

• ensures when you move your head the field of vision stays basically constant
• vestibular system quicker than visual - ion channels and g proteins

Question 18

what does vestibular nystagmus do

Answer 18

• enables resettling of eye position during sustained head rotation
• slow phase: eyes rotate in opposite direction to head movement
• quick phase: rapid resettling movement back to centre of gaze
• quick phase is brainstem stepping in and stopping your eyes moving round your head