Part 2 - Vestibular System

Question 1

What is proprioception?

Answer 1

The awareness of the position and movement of the body; perception of self
- provided by the vestibular, vision, and somatosensory systems

Question 2

Name the 3 parts of the vestibular system

Answer 2

The sensorial organs: the utricle, saccule, and semicircular canals

The vestibular nuclei (the first processor)

The cerebellum (supervisor)

Question 3

Is the vestibular system under our conscious control?

Answer 3

No
- the very fast sensory motor integration is necessary to prevent falls and keep a clear image on the retina; we do not have time to think

Question 4

Name 3 things the vestibular system is responsible for

Answer 4

• assessing movements of the head to maintain postural control
• stabilizing images on the fovea of the retina during head motion
• resolving inter-sensory system conflicts

Question 5

Which part of our system acts as the “judge” in resolving sensory disconnect?

Answer 5

The vestibular system, because it is internally referenced

Question 6

What are the 3 vestibular receptors and their roles?

Answer 6

The 3 semicircular canals
- detect angular accelerations in the 3 planes of space, therefore perceiving head rotations

The utricle
- detects linear accelerations of the head in the horizontal plane

The saccule
- detects linear accelerations of the head in the vertical plane (including gravity)

Question 7

The anterior canal is perpendicular to the ______ (anterior/posterior) canal on the opposite side

Answer 7

anterior

and perpendicular to the posterior canal on the same side

Question 8

What is the enlargement at the base of each semicircular canal called? What does it contain?

Answer 8

The ampulla

• consists of a gelatinous mass called the cupula
• cupula + the cells it rests on = ampullary crest (or crista ampullaris)
• crista ampullaris embeds the hair cells and supporting cells -> vestibular nerve

Question 9

How are the stimuli generated from the semicircular canals?

Answer 9

The endolymph of the semicircular canals moves in the opposite direction of head movement d/t inertia. This motion bends the cupula, activating the hair cells embedded inside and generating a stimulus

Question 10

The motion of the endolymph will be maximal when the canal rotates around its ______(longitudinal/perpendicular) axis

Answer 10

Perpendicular

Question 11

The vestibular hair cells have 50 - 100 hair cells (called ______), the longest of which is called a ________

Answer 11

Stereocilia

Kinocilium

Question 12

Inhibition occurs when the motion of the stereocilia is _____ (towards/away from) the kinocilium

Answer 12

Away from

Question 13

What are the 2 different types of hair cells good at?

Answer 13

Type I appear “flask-like” and are good for rapid detection of head motions or initiating the VOR

Type II are cylindrical and are the regular ones, sensitive to a wide range of motion

Question 14

Since the hair cells have a range of 0 to 400 spikes per second, and a resting rate of 70 to 100 spikes per second, what does this mean regarding excitation and inhibition?

Answer 14

Excitation is higher than inhibition (follows Ewald’s 2nd and 3rd laws)

Question 15

Which canals will be stimulated or inhibited if we look towards our left shoulder?

Answer 15

Right anterior stimulated

Left posterior inhibited

Question 16

When turning right, which horizontal canal is stimulated?

Answer 16

The right (left is inhibited)

Question 17

State Ewald’s 2nd law (Horizontal Canals)

Answer 17

Cupula displacement towards the ampulla generates greater responses that those generated by acceleration with displacement away from the ampulla

Question 18

Displacement towards the ampulla is called _____ and displacement away is called _______

Answer 18

Towards = ampullopetal
Away = ampullofugal

Question 19

For the vertical semicircular canals, we follow Ewald’s 3rd Law, which states:

Answer 19

Ampullofugal displacement will produce greater responses than ampullopetal displacements (opposite to the 2nd law for the horizontal canals)
- the hair cells are arranged differently

Question 20

Contrast Ewald’s 2nd and 3rd Laws

Answer 20

2nd Law (Regarding horizontal SCC's):
Ampullopetal responses > Ampullofugal

3rd Law (Regarding vertical SCCs):
Ampullofugal responses > Ampullopetal

So greater VOR responses will be seen with displacement towards or away from the ampulla, depending on which type of canals we are talking about