Lecture 24: Vestibular System

Question 1

Two components of the vestibular system

Answer 1

1. Semicircular canals- angular acceleration
2. Otoliths- linear acceleration

Question 2

Where is the vestibular organ located?

Answer 2

Temporal bone

Question 3

What supplies blood to the vestibular organ?

Answer 3

AICA, Internal auditory artery

Question 4

Describe vestibular hair cells

Answer 4

• Hair cells have stereocilium that gradually get longer across the cell
• Kinocilium causes hair cells to activate
• Otoliths on top of a fibrous membrane help activate the cells by being displaced during acceleration
• Maculae of the utricle and saccule are in different planes, so they can measure movement in three dimensions

Question 5

Describe the ampulla in the vestibular organ

Answer 5

• At the end of each semicircular canal
• Contain sensory epithelium, cristae, where the hair cells are
• Hair cells embedded in gelatinous mass (cupula)
• Fluid flows past and causes kinocilia when the head is moved
• Info from each ear is integrated to determine movement

Question 6

Where is the vestibular nuclei located in the brainstem?

Answer 6

At the pons/medulla junction

Question 7

Where does the vestibular nuclei project to?

Answer 7

1. Cerebellum for motor correction
2. Contralateral vestibular nerve
3. Extraocular muscles for gaze stabilization
4. Spinal cord via vestibulospinal path for posture adjustment

Question 8

Area of brain that processes vestibular information

Answer 8

Parietal operculum

Bilateral but stronger on ipsilateral side

Question 9

How does the vestibular system interact with the cerebellum?

Answer 9

Vestibular system gives info about where the head is moving so the cerebellum can make corrections

Question 10

What is the vestibulo-ocular reflex?

Answer 10

Keeps the eyes still in place while the head moves

Question 11

What is the vestibulo-cervical reflex?

Answer 11

Keeps the head level when walking

Question 12

What is the vestibular-spinal reflex?

Answer 12

Adjusts posture for rapid changes in position; via vestibulospinal path

Question 13

What does the otolith signal mostly act on?

Answer 13

Spinal cord via lateral vestibulospinal tract in ventral funiculus; ipsilateral

Acts on proximal muscles in legs/arms to adjust for head movements

Question 14

How do semicircular canal inputs reach the spinal cord?

Answer 14

Medial vestibulospinal tract

Mostly but not all ipsi; mostly to cervical segments

Question 15

What semicircular canals sense rotation in which plane?

Answer 15

• Horizontal canals- horizontal plane
• Vertical 45° to the left: LARP
• Vertical 45° to the right: RALP

Question 16

Describe how the vestibular system moves the eyes

Answer 16

Question 17

Optokinetic nystagmus

Answer 17

Eyes will snap to the other direction when the head rotates away from something too far

Question 18

Artificial activation of optokinetic nystagmus

Answer 18

• Inject water into ear
• Cold opposite; warm same (COWS)
• Warm water in left ear causes eyes to turn right and snap back to left
• Cold water in left causes eyes to turn left and snap back to right

Question 19

Benign Paroxysmal Vertigo

Answer 19

Otoliths can fall off membrane and get stuck in cupola and cause hair cells to sense gravity = vertigo in certain position

Can rotate head a certain way to get them back