4 - the vestibular system lecture

Question 1

what does the vestibular system detect and act as?

Answer 1

detects forces generated by movement, acting as an accelerometer

Question 2

the vestibular system translates the forces detected into a sense of what?

Answer 2

balance

Question 3

what does the vestibular system provide information about?

Answer 3

the position of the head in space

Question 4

what effect does the vestibular system have on other CNS structures?

Answer 4

allows other CNS structures (eg. brainstem, cerebellum, basal ganglia etc) to rapidly compensate for changes

Question 5

what is the vestibular system embedded in?

Answer 5

bone (bony/membranous labyrinth)

Question 6

where is the vestibule located?

Answer 6

between the semi-circular canals and the cochlea

Question 7

semi-circular canals vs vestibule

Answer 7

semi-circular canals — balance with MOVEMENT
utricle and saccule — STATIC balance forces

Question 8

the vestibule contains the ____ and ____ which have equilibrium receptors called ____?

Answer 8

1. utricle and saccule
2. maculae

Question 9

describe the saccule

Answer 9

• continuous with the cochlear duct anteriorly
• vertical acceleration (lift)

Question 10

describe the utricle

Answer 10

• continuous with the semi-circular ducts posteriorly
• horizontal acceleration (car)

Question 11

what do the semi-circular canals form and detect?

Answer 11

• form the dynamic system
  -detect angular acceleration

Question 12

what do otolith organs form and detect?

Answer 12

• form the static system
• detect linear acceleration

Question 13

what are the otolith organs?

Answer 13

utricle and saccule

Question 14

what are otoconia?

Answer 14

• calcium carbonate crystals
• form the striola which in turn rests on the otolithic membrane
• give weight

Question 15

what do otolith organs detect?

Answer 15

changes in linear acceleration

Question 16

what layer are the hair cells embedded in?

Answer 16

gelatinous layer

Question 17

describe the unstable system of the otolith organs

Answer 17

• otoconia give weight — wobbly
• sensitive to changes in acceleration
• move to bend hair cells
• depolarisation or hyperpolarisation

Question 18

what are macula?

Answer 18

equilibrium receptors

Question 19

what is endolymph high in?

Answer 19

K+

Question 20

where is endolymph?

Answer 20

in the semi-circular canals/ducts

Question 21

where does signal transduction occur in the semi-circular canals?

Answer 21

in the ampullae (at the base of the canals)

Question 22

what are the semi-circular canals sensitive to and what is this essential for?

Answer 22

pitch, roll and yaw — essential for coordination of eye movement

Question 23

what semi-circular canals are there?

Answer 23

horizontal, superior and posterior

Question 24

the movement of what fluid has an effect in the vestibular system?

Answer 24

endolymph

Question 25

the movement of endolymph has what effect?

Answer 25

- displaces a gelatinous mass known as the CUPULA - this causes a physical strain on HAIR CELLS - the displacement of cells due to the sloshing of endolymph causes either depolarisation or hyperpolarisation > lots of hair cells project into the jelly-like cupula

Question 26

deflection towards vs. away from the kinocilium

Answer 26

towards = increases firing away = decreasing firing

Question 27

what do semi-circular canals allow for?

Answer 27

very rapid detection of changes in angular acceleration of the head

Question 28

what kind of transmission is used in the semi-circular canals?

Answer 28

glutamatergic

Question 29

what does the vestibulo-ocular reflex prevent?

Answer 29

retinal slip

Question 30

describe the vestibule-ocular reflex

Answer 30

- head rotates left, eyes rotate right - left eye: contracts medial rectus, relaxes lateral rectus - right eye : contract lateral rectus, relaxes medial rectus

Question 31

what is Scarpa’s ganglion?

Answer 31

- aka. vestibular ganglion - in internal auditory meatus - ganglion of the vestibular nerve

Question 32

describe the vestibular pathway from the vestibular ganglion

Answer 32

signals travel throguh the vestibular portion of CN VIII into the vestibular nuclei in the brainstem. the vestibular nuclei send projections into the cerebellum, spinal cord, thalamus and nuclei of the oculomotor (III), trochlear (IV) and abducens (VI) nerves

Question 33

what are slow vs fast phase movements triggered by?

Answer 33

slow — mediated by vestibulo-ocular pathway fast — triggered by cerebral cortex

Question 34

how can nystagmus be clinically tested?

Answer 34

- by introducing warm or cold water into the external auditory meatus - causes convention currents in the endolymph — stimulates hair cells as if the head was rotating leading to nystagmus - slow phase is still present in a comatose patient, but not the fast phase (as this is controlled by cortex)

Question 35

what does a dysfunctional slow phase imply?

Answer 35

a lesion in the vestibulo-ocular pathway

Question 36

describe the vestibulo-spinal tract

Answer 36

- basic balance and postural control - axons from vestibular nuclei descend ipsilaterally - synapse on LMNs - activity in the vestibular nuclei is modulated in the cerebellum

Question 37

what is Ménière’s disease?

Answer 37

- vestibular dysfunction - increase in endolymph pressure - disrupts signal transduction and can result in tinnitus, nausea, spontaneous nystagmus (by stimulating these reflexes)

Question 38

what is benign paroxysmal positional vertigo (BPPV)?

Answer 38

- vestibular dysfunction - dislodged bits of otolith stimulate the cupula in the posterior SSC causing vertigo

Question 39

what manoeuvre attempts to nudge the dislodged bits back to the vestibule in BPPV to remove nausea and dizziness?

Answer 39

the Epley manoeuvre

Question 40

when does motion sickness occur? treatment?

Answer 40

when there is a mismatch between data from different sensory modalities and with what the rest of the brain expects to happen (eg. on plane, vestibular system says you’re moving, vision and proprioception says you’re staying still) treat with antihistamines, look at horizon (to match vestibular and visual systems)