Vestibular System

Question 1

What is the function of the vestibular labrynths?

Answer 1

Sense head motion (each canal detects one of three different rotational movements)

Question 2

What are otoliths?

Answer 2

Utricle and saccule

Question 3

What aspects of motion do the vestibular labrynths detect?

Answer 3

Acceleration of the head and intertial forces

Question 4

What does info from the the vestibular system used to generate?

Answer 4

Vestibulo-ocular reflex (VOR)

Question 5

What is the purpose of the VOR?

Answer 5

To keep the visual scene steady on the retina during head movements

Question 6

The output of the vestibular system is proportional to what?

Answer 6

Head velocity

Example:

Head accelerates from 1-10 deg/ sec. The vestibular system detects the acceleration and it integrates over time to determine the head velocity. It then sends a signal to the eye muscles to counter rotate the eyes with a velocity of 10 deg/sec

Question 7

What are the components of the vestibular apparatus?

Answer 7

Ampulla of the superior canal, Saccular macula, Utricular macula

Question 8

Describe the orientation of the hairs in the ampulla:

Answer 8

Hairs are all oriented in the same direction

Question 9

Describe the orientation of the hairs in the saccular macula:

Answer 9

Striola sperates hairs with opposite polarity. Vertical organization

Question 10

Describe the orientation of the hairs in the utricular macula:

Answer 10

Striola sperates hairs with opposite polarity. Horizontal organization.

Question 11

Polarization of what hair cells gives the vestibular aparatus is directional sensitivity?

Answer 11

all three…Ampulla of the superior canal, Saccular macula, Utricular macula

Question 12

What is the significance of the striola?

Answer 12

Orientation of the hair cells relative to the striola in each structure gives continuous representation of ALL body movement directions

Question 13

What are hair cells connected to?

Answer 13

Primary afferent fiber and an efferent fiber

Question 14

Where do apical hair cells of the utricle and sacculus project to?

Answer 14

They project into the otolithic membrane (gelatinous mixture)

Question 15

Is the method of stimulating the hair cells in the ampulla the same as the utricle and sacculus?

Answer 15

No the mechanism is different.

Question 16

What is the otoconia?

Answer 16

Calcium carbonate that gives the gelstinous mixture weight

Question 17

What forces depolarize the hair cells?

Answer 17

Backward head tilt or forward acceleration

Hairs bend toward the kinocilia

Question 18

What forces hyperpolarize the hair cells?

Answer 18

Forward head tilt and forward deceleration

hairs bend away from the kinocilia

Question 19

When considering inertial forces….what directions do the hear cells move?

Answer 19

Displacement of the otolithic membrane and hair cells is in the OPPOSITE direction of the inertial force

Question 20

What does depolarization of hair cells produce?

Answer 20

Increase impulse frequency…this increases the response of the innervating CN 8 fiber

Question 21

What does hyperpolarization of hair cells produce

Answer 21

decrease impulse frequency…this decreases the response of the innervating CN 8 fiber

Question 22

What is kinocilia and steriocilia

Answer 22

the endings of the hair cells. Kinocilia is the tall cilia and it is singular. There are many, smaller sterocilia.

Question 23

What are the three degrees of rotation?

Answer 23

Yaw: z axis
Roll: x axis
Pitch: y axis

Question 24

How do the three degrees of rotation help in the vestibular system?

Answer 24

This is how we detect acceleration and deceleration….it is a very sensitive system

Question 25

The left anterior canal works with……

Answer 25

the right posterior canal

Question 26

The right anterior canal works with….

Answer 26

the left posterior canal

Question 27

What is the cupula?

Answer 27

a gelatinous membrane extending from the ampullary crest to the top of the ampulla

Question 28

Whta displaces the cupula?

Answer 28

the cupula is displaced by the inertia of the fluid in the semicircular canals due to angular acceleration or deceleration of the head

Question 29

If you move your yead to the right…which way does the fluid/ cupula move?

Answer 29

to the left

Question 30

Where do the cilia of hair cells project in the canals?

Answer 30

Into the cupula

Question 31

Why do pairs of canals on opposite sides of the head work together?

Answer 31

To provide bilateral information about rotation

Question 32

Does left rotation excite or inhibit left CN 8 and vestibular nuclei?

Answer 32

Excite (and it inhibits the right CN8 and VN)

Question 33

When you turn your head left and the left vestibular nuclei gets excited…what does the left VN then excite?

Answer 33

1. The right abducens nuclei (which then activates the right lateral rectus muscle
2. the MLF (which then excites the left oculomotor nucleus –CN 3)

Question 34

When resting, what are the vestibular nerves doing?

Answer 34

maintaining a resting discharge when there is no head movement

Question 35

What happens in pathologic conditions?

Answer 35

No activity is coming from one of the canals and when there is comparison of the activity from the two canals, it is interpreted as rotation to the side that is firing as normal (away from the silent side)

Question 36

Describe the nystagmus that results in a pathologic condition?

Answer 36

Slow eye movements toward the silent side and then a quick reset to the normally firing side (the side your brain thinks you are rotating towards)