vestibular system

Question 1

anatomy of the ear

Answer 1

Question 2

role of vestibular system

Answer 2

• not prominent conscious sensation
• reflexes evoked (equilibrium/balance & stabilization of visual field)

Question 3

2 suborgans of vestibular system

Answer 3

• semicircular canals
• otolith (macular) organs

Question 4

semicircular canals function

Answer 4

• sense angular acceleration (turning head)
• inertial mechanism
• rapidly adapting (phasic) receptors

Question 5

otolith (macular) organs

Answer 5

• sense linear acceleration and static position of the head
• gravitational mechanism
• slowly adapting (tonic) receptors

Question 6

semicircular canals structure

Answer 6

• filled with endolymph
• ampulla
• crista ampullaris
• hair cells
• cupula (watertight seal)

Question 7

each canal has an expansion called

Answer 7

ampulla which contain the endolymph

Question 8

hair cells are located within

Answer 8

the ampulla of the semicircular canals

Question 9

ampulla is innervated by

Answer 9

CN VIII

Question 10

cupula extends to

Answer 10

the top of the ampulla to divide the sides from each other
- important to only allow hair cells to go side to side

Question 11

hair cells

Answer 11

• flask (I) and tube (II) shapes
• 1 kinocilium (larger)
• 100 stereociia (smaller)
• synaptic vesicles

Question 12

depolarization and hyper polarization of hair cells

Answer 12

• to depolarize: kinocilium pushed away from stereocilium (then release neurotrasnmitter) because open channels
• to hyperpolarize: kinocilium pushed toward the stereocilium (less transmitter release) beacuse closed channels

Question 13

hair cells have ________ firing rate

Answer 13

high

Question 14

signaling to release neurotrasmitters of hair cells

Answer 14

• the kinocilium pulls away from the sterocilia
• the mechanically gated channels open up
• K+ to flow in >
• depolarization >
• Ca2+ flows in >
• synaptic vesicles release transmitter into
  synaptic cleft >
• activation of afferent nerve (CN VIII)

Question 15

vestibular afferents

Answer 15

• vestibular branch of CN VIII
• cell bodies in vestibular (Scarpa’s) ganglion
• have high firing rate

Question 16

endolymph - relative motion

Answer 16

• head moves to the right
• canal moves in that direction
• endolymph is fluid so it stays put by inertia
  differential movement
• pushes cupula in that direction

Question 17

orientation of sterocilia - horizontal canal

Answer 17

I = inhibition
E = excitation

Question 18

each semicircular canal transduces

Answer 18

angular velocity in plane of duct

Question 19

there is no signal if movement is

Answer 19

normal to plane of duct

Question 20

if rotation is at an angle to plane of duct

Answer 20

signal is a vector fraction

Question 21

otolith organs structure

Answer 21

• macula is a patch of hair cells
• covered by gelatinous mass
• otoconia embedded in mass
• otoconia are CaCO3 crystals

Question 22

otolith organs orientation

Answer 22

• located in saccule and utricle
• utricular macula is horizontal
• saccular macula is vertical

Question 23

otolith organ physiology

Answer 23

• shearing forces act on otoconia
• otoconial movements cause stereocilia to be deflected

Question 24

shearing forces are produced by

Answer 24

1. linear acceleration or deceleration
2. tilting of the head

Question 25

reflexes evoked by vestibular stimulation

Answer 25

1. maintenance of equilibrium 2. stabilization of visual orientation

Question 26

maintenance of equilibrium afferent fibers connect to

Answer 26

lateral vestibulospinal tract (extensor muscles of the eye) - abducens, oculomotor, trochlear nuclei

Question 27

stabilization of visual orientaiton afferent fibers connect to

Answer 27

medial longitudinal fasciculus (MLF) - this binds the 3 nuclei of eye movement

Question 28

vestibular afferents terminate in

Answer 28

- vestibular nuclei (border between medulla and pons) - cerebellum

Question 29

vestibular nuclei | #? projects down what tract? CN?

Answer 29

- 4 total (superior, lateral, inferior, medial) - lateral = projects down through spinal cord (LVST) - CN VIII distributes to all 4 nuclei

Question 30

vestibular nuclei efferents

Answer 30

1. to abducens, trochlear, oculomotor nuclei via ascending MLF 2. to neck motor neurons via descending MLF 3. to limb and trunk motor neurons via LVST 4. to cerebellum 5. to reticular formation 6. to VPM and cerebral cortex

Question 31

loss of vestibular function symptoms

Answer 31

- difficulty maintaining balance - visual disturbances while walking - nystagmus - vertigo - nausea

Question 32

vestibular system disorders

Answer 32

- Benign positional vertigo - meniere's disease - acoustic neuroma - ototoxic drugs - trauma

Question 33

motion sickness occurs when

Answer 33

motion signals transmitted by the eyes, vestibular system, and proprioceptors are at a variance with one another or with what is expected from previous experience

Question 34

motion sickness evokes what?

Answer 34

- autonomic reactions (nausea, vomiting, pallor, sweating, hypersalivation, stomach awareness) - drowsiness - fatigue

Question 35

continued exposure of motion sickness leads to

Answer 35

disappearance of reactions - "sensory conflict and neural mismatch" theory