Vestibular system

Question 1

Where does the vestibular system lie?

Answer 1

Deep within the temporal bone adjacent to the cochlea

Question 2

What is the vestibule, where does it lie, what does it communicate with?

Answer 2

Central part of the bony labyrinth.

Communicates anteriorly with the cochlea and posteriorly with the semi-circular canals.

Question 3

How is the vestibule separated from the middle ear?

Answer 3

Oval window

Question 4

What are the three semi-circular canals?

Answer 4

Anterior, lateral and posterior

Question 5

What lies inside the vestibule?

Answer 5

Saccule and utricle

Question 6

Where does endolymph from the saccule and utricle drain?

Answer 6

Into the endolymphatic duct

Question 7

Endolymph composition

Answer 7

High K+ content (like ICF)

Question 8

Where do cell bodies of vestibular nerves lie?

Answer 8

Vestibular ganglia

Question 9

Where do vestibular nerves project to?

Answer 9

Vestibular nuclei (medial, lateral, superior and inferior) and cerebellum

Question 10

What are ampullae?

Answer 10

Swellings at the base of the semi-circular canal where sensory receptors lie

Question 11

Where do ampullae stereocilia project?

Answer 11

Into gelatinous cupula

Question 12

What movements do semi-circular canals respond to?

Answer 12

Rotation and angular acceleration

Question 13

What happens in the ampullae upon angular acceleration?

Answer 13

Endolymph lags behind the head due to the inertia of the fluid, this flexes the cupula and bends the cilia

Question 14

What happens when hair cells bend towards the kinocilium?

Answer 14

Hair cell depolarises and leads to increased glutamate release onto CNVIII which generates a train of action potentials in the vestibular nerve

Question 15

What happens when the hair cells bend away from the kinocilium?

Answer 15

Hair cells hyperpolarize leading to inhibition of transmitter release.

Question 16

Does hair cells stimulation cause discharge?

Answer 16

No, only increase/decrease discharge rate compared to tonic resting position.

Question 17

What happens inside the semi-circular canals in rotation?

Answer 17

Displacement of the fluid in the horizontal canal -activating the vestibular system on one side (rapid firing increase), whilst inhibiting it on the other side.

Question 18

How long does the vestibular response to head rotation in one direction last and why?

Answer 18

Happens immediately but ceases after several seconds (about 6 secs) (falling to zero) even when the head is still rotating - this is because the fluid starts to rotate as well, hair bundle is no longer deflected.

Question 19

What happens inside the semi-circular canals when the head stops rotating?

Answer 19

Endolymph continues to move around, we perceive this as the opposite, causing an imbibition of the stereocilia

Question 20

What are the axes that the semi-circular canals detect?

Answer 20

Pitch (y-axis nodding yes), roll (x-axis shoulder to shoulder), yaw (z-axis shaking no)

Question 21

Each semicircular canal (anterior, posterior or horizontal) responds maximally to

Answer 21

A rotation about an axis perpendicular to its plane.

Question 22

Fibres from the horizontal and anterior canals primarily synapse in the

Answer 22

Superior, lateral and medial nuclei

Question 23

Fibres from the posterior canals primarily synapse in the

Answer 23

Superior, descending (inferior) and medial nuclei

Question 24

In the saccule and utricle what do the hair cells project into?

Answer 24

Gelatinous otolithic membrane and is overlaid by otoconia/otoliths

Question 25

What is the otolithic membrane covered by (saccule and utricle)?

Answer 25

Otoconia/otoliths

Question 26

What are otoconia/otoliths?

Answer 26

Calcium carbonate crystals that have inertia.

Question 27

What are type I hair cells?

Answer 27

Surrounded by an afferent calyx

Question 28

What are type II hair cells

Answer 28

More efferents that synapse directly on the hair cell body (punctate boutons)

Question 29

How is the saccule/utricle membrane divided?

Answer 29

Central striola, on either side there is a division of hair cell type

Question 30

What does the saccule detect?

Answer 30

Vertical linear acceleration

Question 31

What does the utricle detect?

Answer 31

Horizontal linear acceleration

Question 32

Why are hair cells arranged in the way they are in the saccule and utricle?

Answer 32

So they can detect changes in motion in any direction

Question 33

What responds to gravity?

Answer 33

Saccule and utricle

Question 34

Afferents from the utricle and saccule terminate mainly in the

Answer 34

Inferior and medial nucleus. Lateral nuclei receive synapses from saccule and utricle too.

Question 35

Vertigo

Answer 35

Inputs from vestibular system do not match environment

Question 36

How does the cerebellum influence the VOR?

Answer 36

Visual feedback that can detect errors in the VOR is too slow to correct the very rapid responses generated by the VOR during a head movement. These adaptive changes are lost following a lesion of the cerebellar flocculus.

Question 37

The vestibular part of the cerebellum is the

Answer 37

Flocculus and nodulus

Question 38

Benign paroxysmal positional vertigo (BPPV)

Answer 38

Pieces of otolithic membrane break off and fall into semi-circular canal displacing fluid. Common in elderly.

Question 39

Meniere's disease

Answer 39

Improper drainage of endolymph via endolymphatic duct. Gentamycin can be used to kill hair cells in severe cases.

Question 40

Vestibular nystagmus

Answer 40

VOR rapid eye movement and slow movement to reset eye gaze Vestibular nystagmus is normal when a person is being rotated.

Question 41

Egocentric coordinate system.

Answer 41

Relative position of parts of body with respect to each other

Question 42

Exocentric coordinate system.

Answer 42

Relative position of body with respect to environment

Question 43

Geocentric coordinate system.

Answer 43

Orientation of body in gravitational field

Question 44

Vestibulocollic reflex

Answer 44

Neural reflex that activates neck muscles when head motion is sensed by the vestibular organs in the inner ear Mediated by the medial vestibulospinal tract

Question 45

The semi-circular canals lie within the...

Answer 45

Petrous part of the temporal bone

Question 46

The semi-circular canals are concerned with...

Answer 46

Angular acceleration

Question 47

The nerves innervating the utricle and saccule arise in the...

Answer 47

Vestibular ganglion

Question 48

The vestibular nuclei have strong interconnections with the...

Answer 48

Oculomotor nuclei

Question 49

The major target of the output from the vestibular part of the cerebellar cortex is the..

Answer 49

Fastigeal nucleus