Vestibular

Question 1

What are the 3 general “balance” systems and how many at a time are essential for balance?

Answer 1

• Vestibular, proprioceptive, and visual systems

- 2 out of 3

Question 2

What are the 3 main structural parts of the vestibular apparatus?

Answer 2

1. Semicircular canals (SSCs)- ant/horizontal/post
2. Utricle- connects the 3 canals
3. Saccule- continuous w/the cochlea

Question 3

What is the main things that the semicircular canals measures?
Utricle?
Saccule?

Answer 3

• SSC: Angular/rotational motion
• Utricle: Primary gravity sensor (upright position/head tilt); horizontal linear accelleration
• Saccule: Detects general orientation and vertical linear accelleration

Question 4

What’s the name of the part of the semicircular canals that contains the hair cells?
What’s the name of the gelatinous substance covering the hair cells?

Answer 4

• Ampulla

- Cupula

Question 5

What is the physics term for why the hair cells bend w/head rotation?
How sensitive are they?

Answer 5

Inertial displacement, sensitive to accelleration (not velocity)
- 0.1 degree/sec^2 (very)

Question 6

Generally explain how inertial displacement affects the cupula.

Answer 6

Movement of the head results in an inertial displacement of the fluid, pushing the cupula in the opposite direction in the canal

Question 7

How does inertial displacement affect perception?

Answer 7

Differential displacement of the hair cells on the left and right horizontal canals causes the cortex to perceive these corresponding increases and decreases in output as directional movement (left or right) with a specific “velocity.”
The greater the difference, the faster the perceived velocity.

Question 8

How does alcohol affect our perception during inertial displacement?

Answer 8

If you change relative output b/w the 2 sides (ETOH alters their conduction velocity), it’s perceived as movement…brain thinks you’re moving in that particular direction…vertigo

Question 9

Explain how the hair cells of the 3 canals are paired and how they’re oriented w/respect to the utricle.

Answer 9

• Ant canal on R paired w/post canal on L. Ant canal on L paired w/post canal on R. Ant and post canals oriented away from the utricle.
• Horizontal canals are paired, oriented toward the utricle.

Question 10

How many stereocilia and kinocilia are their per hair cell in the SSC?

Answer 10

• 1 large kinocilium

- 40-70 stereocilia (linked to the kinocilium)

Question 11

How are hair cells depolarized/hyperpolarized?

Answer 11

• Bending towards kinocilium causes depolarization (AP more likely). Bending away causes hyperpolarization. Bending perpendicular has no effect.
• Gives hair cell orientation axis.
• They have tonic output; never give off APs (AP occur in bipolar cells of vestibular n.).

Question 12

What is the main difference b/w the tectorial membrane of the cochlea and the cupula covering the hair cells of the utricle and saccule?
What’s the functional reason?

Answer 12

Contains otolithic granules (Ca carbonate crystals), known as otolithic membrane.
- Allows perception of gravity–changes w/head position

Question 13

Explain the pw of input from a hair cell to the CNS.

Answer 13

*Hair cell > bipolar cell (AP) > vestibular ganglion > CN VIII > vestibular nuclei

Question 14

Is the posterior saccule and posterior SCC in the inferior or superior division of the vestibular ganglion?
What’s in the other ganglion?

Answer 14

• Inferior division (everything else is in superior division)

Question 15

On cross section, where on the brainstem would you find the vestibular nuclei?

Answer 15

*Rostral medulla/caudal pons, posterior and medial to inferior cerebellar peduncles

Question 16

*What do the ascending fibers of the medial longitudinal fasciculus (MLF) control?
What else is important about the MLF’s functional relation the vestibular system?

Answer 16

Eye movements

- Connects III, IV, and VI to the vestibular system

Question 17

What do the descending fibers of the medial longitudinal fasciculus control?

Answer 17

Head and neck movements

Question 18

What part of the cerebellum is the vestibular system associated with?
What gives it direct input? What gives it indirect input?

Answer 18

Flocconodular lobe

• Direct input from SSC and otolithic organs
• Indirect input from vestibular nuclei, LGN, sup colliculus, and pontine nucleus

Question 19

What are 2 main reasons why the cerebellum would send info back to vestibular nuclei?

Answer 19

• To control axial and proximal limb muscles associated with balance and posture
• To control eye movements and coordination of head & eye movements.

Question 20

• Lateral vestibulospinal tract:
• Name the nucleus.
• Crossed or uncrossed?
• Length along sc?
• What does it act on and why?

Answer 20

• Lateral vestibulospinal nucleus
• Uncrossed
• Entire length of sc
• Acts on proximal limb mm. to control balance

Question 21

• Medial vestibulospinal tract:
• Name the nucleus.
• Crossed or uncrossed?
• Length along sc?
• What does it act on and why?

Answer 21

• Medial vestibulospinal nucleus
• Uncrossed (bilateral)
• Cervical sc only
• Acts on neck mm. (head stays erect)

Question 22

When we use the vestibular system to stabilize our gaze, what is the effector system?
What major parts of the brain are involved?

Answer 22

Extra-ocular mm.

- Vestibular system, cerebral cortex, cerebellum, brainstem

Question 23

What is the function of the vestibular-ocular reflex (VOR)? How does it work?
What would happen w/o it?

Answer 23

• Stabilizes the image on the retina during a rotation of the head *faster than visual tracking. As the head rotates the VOR rotates the eyes with the same speed, but in the opposite direction
• W/o it, image would appear smeared on retina

Question 24

What nucleus accounts for the image stabilization that occurs during the vestibulo-ocular reflex?

Answer 24

Nucleus prepositus hypoglossi

attenuates w/tonic stimulation

Question 25

Explain what's happening at all levels of the VOR when the head is rotating to the right while looking at a stationary image.

Answer 25

* Both eyes will move to the left... - R horizontal canal is activated - R vestibular nucleus is activated - L CN VI nucleus is activated (via PPRF), L lateral rectus m. contracts - Left PPRF activates neurons in R CN III nucleus, R medial rectus contracts PPRF: Paramedian pontine reticular formation. Also, *MLF important for eye movement coordination.

Question 26

Explain the basics of nystagmus.

Answer 26

- Definition: Rhythmic back-and-forth movement of eyes (often involuntary; usually horizontal but can be vertical or rotary) - Usually the movement is slow in one direction (“smooth”) and fast (“saccadic”) in the other

Question 27

Explain the steps that occur in nystagmus when you induce it by spinning yourself around.

Answer 27

1. The VOR is generating the slow phase which helps to keep an eye on a target 2. Once the eye approaches the maximum that it can turn, a saccade will then occur moving the eyes in an opposite direction and onto a new target (Optokinetic nystagmus or OKN)

Question 28

How do you test clinically for nystagmus?

Answer 28

Caloric test - Hot and cold water produce currents in opposite directions and therefore a horizontal nystagmus in opposite directions. - COWS: Cold Opposite, Warm Same. (fast phase) Cold water = FAST phase of nystagmus to the side Opposite from the cold water filled ear Warm water = FAST phase of nystagmus to the Same side as the warm water filled ear

Question 29

Explain 3 ways we can become dizzy w/o illness?

Answer 29

1. Vestibular system activated w/o visual system (spin in chair w/eyes closed, vestibular system attenuates) 2. Sense of motion via visual system w/o vestibular confirmation - "a disconnect" (like in the automatic carwashes) 3. Sense of motion via vestibular system w/o visual confirmation - "a disconnect" (being in boat cabin during storm > motion sickness)

Question 30

A virus invades the stria vascularis cells of the left inner ear, resulting in a significant increase in the concentration of potassium in the endolymph. Which one of the following would you expect to happen? A. The outer hair cells hyperpolarize, causing a high pitched “ringing” in the ears. B. The patient complains of muffled sounds due to smaller receptor potentials in the inner hair cells. C. The hair cells in the left ampulae depolarize to a greater extent than those on the right, and the patient complains of vertigo/dizziness. D. The otoconia hyperpolarize, and the patient feels “light-headed.”

Answer 30

C. The hair cells in the left ampulae depolarize to a greater extent than those on the right, and the patient complains of vertigo/dizziness.

Question 31

When you voluntarily turn your head to the left, which one of the following events will occur in the vestibular system? A. Kinocilia in the ampullae of all the semicircular canals will be simultaneously activated. B. Movement of the stereocilia in the left horizontal canal move towards the kinocilia, resulting in depolarization of the hair cell. C. The medial and superior vestibular nuclei will be inhibited by the afferent fibers from the semicircular canals. D. The velocity of the movement is detected by the otolithic granules in the anterior and posterior semicircular canals. E. Compensatory eye movements will likely be inhibited by the descending MLF.

Answer 31

B. Movement of the stereocilia in the left horizontal canal move towards the kinocilia, resulting in depolarization of the hair cell.

Question 32

Vestibular function is tested in a 19-year-old man using the caloric test. Assuming a normal outcome, which one of the following is most likely to occur when warm water is introduced into the man’s RIGHT ear? A. Horizontal nystagmus, fast phase directed left. B. Horizontal nystagmus, fast phase directed right. C. Occular counter-roll (eversion of eyeball) to the right. D. Vertical nystagmus, fast phase directed downward. E. Vertical nystagmus, alternating fast phases.

Answer 32

B. Horizontal nystagmus, fast phase directed right

Question 33

Which of the following contain an otolithic membrane? - Semicircular canals - Utricle - Saccule

Answer 33

- Utricle | - Saccule