vestibular system

Question 1

what type of cells are found in the
vestibular apparatus of the inner
ear

Answer 1

hair cells

Question 2

what is the vestibular apparatus

Answer 2

a connected series of
ENDOLYMPH-FILLED,
membranous tubes that also
connect with the cochlear duct

Question 3

what do hair cells in the vestibular apparatus do

Answer 3

detect changes in the motion and position of the head by a stereocilia transaction mechanism

Question 4

what does the vestibular apparatus consist of

Answer 4

• 3 membranous SEMICIRCULAR
  CANALS
• 2 saclike swellings
  • the UTRICLE
  • the SACCULE

all of which lie in the temporal bone on either side of the head

Question 5

what do semicircular canals do

Answer 5

Detect angular acceleration during the ROTATION of the head along three
perpendicular axes

Question 6

what activates semi circular canals (3)

Answer 6

1. nodding the head up and down
2. shaking the head from side to side
3. tipping the head so that the ear
   touches the shoulder

Question 7

what do receptor cells of semicircular canals contain

Answer 7

stereocilia

Question 8

what are semi circualr canals stereocilia encapsulated in

Answer 8

within a gelatinous mass - the CAPULA

it extends across the lumen
of each semicircular canal at the
ampulla (a slight bulge in the
wall of each duct)

Question 9

what happens whenever the head moves

Answer 9

the semicircular canal within its bony
enclosure and the attached bodies of the hair cells all move with it

BUT the fluid (endolymph) filling the duct is not attached to the skull,
so due to inertia it doesn’t movie

so the moving ampulla is pushed against the stationary fluid which in
turn causes bending of the stereocilia and the alteration in the rate of
release of glutamate from the hair cells

Question 10

what does glutamate do

Answer 10

crosses the synapse and activates neurones associated with the hair cells, initiating the propagation of action potential towards the brain

Question 11

what do the speed & magnitude of rotational head movements determine

Answer 11

the direction in which the stereocilia are bent and which hair cells are stimulated

Question 12

what do the hair cells release at rest

Answer 12

glutamate

the release increases or decrease from the resting rate according to the direction in which the hairs are bent

Question 13

what causes depolarisation and hyperpolarisation of each hair cell receptor

Answer 13

each hair cell receptor has one direction of maximum neurotransmitter release so when its stereocilia are bent in this direction, the
receptor cell depolarises.

When the stereocilia are bent in the opposite direction the cell hyperpolarises

Question 14

what happens when the head continuously rotates at a steady velocity

Answer 14

the duct fluid begins to move at the same rate as the rest of the head and the stereocilia slowly return to resting position - thus hair cells are only stimulated during acceleration or deceleration

Question 15

what causes nystagmus

Answer 15

1. damage to the canals of one side
   - with the slow phase towards the
   damaged side and the rapid reset away from the damaged side
2. Pouring ice cold water into the external auditory meatus can cause
   convection currents in the semicircular calls

Question 16

what do the Utricle & Saccule (Otolithic organs) do

Answer 16

provide information about linear acceleration of the head, and about the
changes in head position in relation to gravity

Question 17

when do hair cells in the utricle respod

Answer 17

they point nearly straight up when standing and they respond when the the head is tipped away from the horizontal plane or to linear accelerations in the horizontal plane

Question 18

when do hair cells in the saccule respond

Answer 18

they project at right angles to those of the utricle and they responded when you move from lying to a standing position or to vertical accelerations like those produced when jumping on a trampoline

Question 19

what are the stereocilia projecting from the hair cells covered by

Answer 19

a gelatinous substance in which tiny stones known as otoliths are embedded

Question 20

what do the stereocilia of hair cells project into

Answer 20

into the otolithic membrane

Question 21

what makes the gelatinous substance heavier than the surrounding endolymph

Answer 21

The otoliths with are calcium carbonate crystals

Question 22

what does the gelatinous otolithic material do in response to a change in position

Answer 22

it moves according to the forces of gravity and pulls against the hair cells so that the stereocilia on the hair cells bend and the receptor cells are stimulated and the action potential is propagated via the VESTIBULAR NERVE
(branch of the vestibulocochlear nerve (CNVIII))

Question 23

3 uses of vestibular information

Answer 23

1. Control of eye muscles so that in spite of changes to head position, the
   eyes can remain fixed on the same point. Nystagmus is a large,jerky,
   back-and-fourth movement of the eyes that can occur in response to
   unusual vestibular input in healthy people, but can also be used as a sign of pathology
2. Reflex mechanisms of maintaining upright posture & balance. The
   vestibular apparatus plays a role in the support of the head during
   movement and orientation of the head in space
3. Conscious awareness of the position & acceleration of the body,
   perception of the space surrounding the body and memory of spatial
   information - i.e PROPRIOCEPTION

Question 24

where do the central processes of vestibular fibres mostly end

Answer 24

in the vestibular nuclei of
the rostral medulla