Case 4 - Labyrinth

Question 1

what does the vestibular system do

Answer 1

• monitors the position and movement of the head
• gives us our sense of balance and equilibrium
• helps coordinate movements of the head and eyes
• allows adjustments to body posture

Question 2

what does the vestibular system use to transduce movements

Answer 2

hair cells

Question 3

what do the otolith organs do

Answer 3

detect the force of gravity and tilts of the head

Question 4

what do the semi circular canals do

Answer 4

sensitive to head rotation

Question 5

what is the purpose of these two structures

Answer 5

transmit mechanical energy, derived from head movement to its hair cells

Question 6

what does each hair cell of the vestibular organs make

Answer 6

an excitatory synapse with the end of a sensory axon from the vestibular nerve, branch of the vestibulocochlear nerve CNVIII

Question 7

where do the cell bodies of the vestibular nerve axons lie

Answer 7

in scarpa’s ganglionb

Question 8

what is endolymph low and high in

Answer 8

high in K+ and low in Na+

Question 9

where does the perilymph lie and what is it made of

Answer 9

between the bony walls and the membranous labyrinth and is low in K+ and high in Na+

Question 10

what do the hair cells do within each ampulla

Answer 10

extend their hair bindles into the endolmyoh of the membranous labyrinth

Question 11

what do tight junctions do

Answer 11

seal the apical surfaces of the vestibular hair cells, ensuring that endolymph selectively bathes the hair cell bundle while remaining separate from the perilymph surrounding the basal potion of the hair cell

Question 12

what do movements of the stereo cilia towards the kinocilium do

Answer 12

opens mechanically gated transduction channels located at the tips of the stereo cilia

this causes depolarisation of the hair cells causing neurotransmitter release onto the vestibular nerve fibres

Question 13

what is the nature of the receptor potential and what does this mean

Answer 13

has a biphasic nature and this means that some transduction channels are open in the absence of stimulation, with the result that hair cells tonically release neurotransmitter, thereby generating considerable spontaneous activity in the vestibular nerve fibres

Question 14

what are the hair cells in the ampulla all doing

Answer 14

polarised in the same direction

Question 15

what divides the utricle and saccule hair cells

Answer 15

the striola divides the two populations which have opposing polarities

Question 16

what do both the utricle and saccule contain

Answer 16

sensory epithelium, the macula which consists of hair cells and associated supporting cells

Question 17

what overlies the hair cells and their hair bundles

Answer 17

a gelatinous layer, above this layer is a fibrous structure

Question 18

what is this fibrous structure

Answer 18

the otolithic membrane, in which are embedded crystals of calcium carbonate called otoliths

Question 19

what does the striola form

Answer 19

an axis of mirror symmetry such that hair cells on opposite sides of the striola have opposing morphological polarisations

Question 20

what would a tilt along the axis of the striola do

Answer 20

excite the hair cells on one side while inhibiting the hair cells on the other side

Question 21

which way is the saccular macula orientated

Answer 21

vertically

Question 22

which way is the utricular macula orientated

Answer 22

horizontally

Question 23

what happens to the change in firing rate in response to a given movement

Answer 23

can either be sustained or transient, thereby signalling either absolute head position or linear acceleration

Question 24

what motion is the utricle concerned with

Answer 24

horizontal