Vestibular system

Question 1

What does the vestibular system determine?

Answer 1

Which way is up/down and direction of movement

Question 2

How many organs does the vestibular system use to measure head acceleration?

Answer 2

5 organs

Question 3

Where does the output of vestibular organs flow to?

Answer 3

Vestibular nuclei in brainstem

Question 4

What is the function of the vestibular nuclei?

Answer 4

Control of posture & balance

Question 5

What are the two types of accelerations transduced by the utricle and saccule?

Answer 5

Linear accelerations

Question 6

What do the three semi-circular canals transduce?

Answer 6

Angular accelerations of the head

Question 7

What type of fluid is endolymph?

Answer 7

Extracellular fluid rich in K+ & poor in Na+/Ca2+

Question 8

What is the shape of hair cells in the vestibular labyrinth?

Answer 8

Flask shaped

Question 9

What connects the end of stereocilia to adjacent stereocilia?

Answer 9

Tip link

Question 10

What happens when stereocilia are deflected towards kinocilium?

Answer 10

Ion channels open, depolarization occurs, and transmitter release increases

Tip link physically connected to ion channel at 1 end SO stretching of stereocilia cause opening of cation channels

Question 11

What is the role of hair cells in the vestibular system?

Answer 11

Mechanoelectrical transducers

Question 12

How do hair cells communicate with underlying neurons?

Answer 12

By releasing neurotransmitters, increasing firing rate

Question 13

What cranial nerve structure is associated with the vestibular system?

Answer 13

8th cranial - composed of cochlear and vestibular nerves

Question 14

What is the approximate number of myelinated axons in the 8th cranial nerve?

Answer 14

~20,000 myelinated axons

Question 15

What do otolithic organs consist of?

Answer 15

Utricle & saccule

Question 16

What is the orientation of the macula in the utricle?

Answer 16

Horizontal plane

Question 17

What is the function of octoconia in the otolithic organs?

Answer 17

Fine, dense particles of calcium carbonate embedded in + lie on otolithic membrane.

- These fill endolymphatic cavities of utricle & saccule

When the head moves or tilts, the otoconia shift against the hair cells in the utricle and saccule, bending the hair bundles and generating electrical signals.

Question 18

What detects angular acceleration in the vestibular system?

Answer 18

3 semi-circular canals

Question 19

What is the gelatinous diaphragm in semi-circular canals called?

Answer 19

Cupula

Question 20

What is the primary role of the anterior-posterior combination in the ears?

Answer 20

Allow complex detection of movement

Question 21

What is dizziness a result of?

Answer 21

Fluid rotates at the same speed as rotation, pushing hair cells even when rotation has stopped

Question 22

What is Meniere’s disease characterized by?

Answer 22

Sporadic, relapsing vertigo, tinnitus, & distorted hearing

Question 23

What is the main input to vestibular reflexes?

Answer 23

Output of labyrinths

Question 24

What are vestibulo-ocular reflexes responsible for?

Answer 24

Keeping images on eyes still when head moves

Question 25

How many major nuclei compose the vestibular complex?

Answer 25

4 major nuclei

Question 26

What are the 4 vestibular nuclei?

Answer 26

* Medial nucleus * Lateral nucleus * Superior nucleus * Descending nucleus

Question 27

What type of neurons does the medial nucleus contain?

Answer 27

Excitatory neurons

Question 28

What do lateral nuclei primarily output to?

Answer 28

Lateral vestibulospinal tract

Question 29

What is the function of the descending nucleus?

Answer 29

Integrates central motor signals with vestibular signals

Question 30

What is the main function of vestibular-ocular reflexes (VOR)?

Answer 30

Compensate for head movements to stabilize gaze on an object ## Footnote VOR helps maintain visual stability by adjusting eye movements in response to head motion.

Question 31

How does the vestibular system communicate head movement to the oculomotor system?

Answer 31

By sending signals about the speed and direction of head rotation ## Footnote This communication allows for the proper adjustment of eye movements.

Question 32

What are the three forms of VOR?

Answer 32

* Rotational vestibulo-ocular reflex * Translational vestibulo-ocular reflex * Ocular counter-rolling response

Question 33

What does the rotational vestibulo-ocular reflex compensate for?

Answer 33

Head rotation ## Footnote Eyes rotate slowly in the opposite direction of the head movement.

Question 34

What is vestibular nystagmus?

Answer 34

A combination of slow and quick eye movements in a repetitive pattern ## Footnote It can indicate clinical problems if constant when a scene is stationary. - issue w/ rotational VOR

Question 35

What is the challenge with the translational vestibulo-ocular reflex?

Answer 35

It must account for the distance of the object being viewed ## Footnote This adds complexity compared to the rotational VOR.

Question 36

What is the function of the ocular counter-rolling response?

Answer 36

Compensates for head tilt in the vertical plane ## Footnote This response helps maintain visual stability relative to gravity.

Question 37

What role does the optokinetic reflex play in visual processing?

Answer 37

Compensates for eye movement to keep images stationary in perception ## Footnote It helps stabilize the visual field during head movements.

Question 38

True or False: The optokinetic reflex works best with fast visual image motion.

Answer 38

False ## Footnote It is activated by very slow visual image motion.

Question 39

What happens during circular vection?

Answer 39

A perception of self-motion occurs when large parts of the scene move ## Footnote This can induce a false sensation of rotating around a stationary cylinder.

Question 40

How do vestibular and optokinetic inputs interact during prolonged rotation?

Answer 40

Vestibular input decays while optokinetic pathways generate a rising signal ## Footnote This interaction can lead to a false vestibular-like sensation.

Question 41

What are vestibulospinal reflexes responsible for?

Answer 41

Posture maintenance and early warning of odd postures ## Footnote They play a crucial role in balance.

Question 42

Define static equilibrium.

Answer 42

Balance of forces acting on the body at rest ## Footnote This is a key component of posture regulation.

Question 43

What is dynamic equilibrium?

Answer 43

Balance when the body is in motion ## Footnote It is important for maintaining stability during movement.

Question 44

How can posture be modified by learning?

Answer 44

Through classical conditioning to adjust center of gravity ## Footnote For example, cats can learn to shift their weight when losing support from one paw.

Question 45

What happens to adaptive postural control in cerebellar lesion patients?

Answer 45

They are unable to make adaptive changes in posture ## Footnote This can lead to falls and overcompensation.

Question 46

What is the impact of damage to the vestibular system?

Answer 46

Subjects quickly lose balance ## Footnote This highlights the vestibular system's importance in maintaining stability.

Question 47

What does the gaze reflex coordinate?

Answer 47

Head and eye movements towards a point of interest ## Footnote This ensures visual focus during movement.

Question 48

Fill in the blank: The vestibular system provides _______ input that is faster than visual input for posture maintenance.

Answer 48

vestibular