Exam #6: Vestibular Function

Question 1

What is the utricle? What is the function of the utricle?

Answer 1

This is an otolith organ that contains a macula with hair cells

• Oriented horizontally
• Contains calcium carbonate crystals
• Respond to LINEAR motion

Question 2

What is the saccule? What is the function of the saccule?

Answer 2

This is an otolith organ that contains a macula with hair cells

• Oriented vertically
• Contains calcium carbonate crystals
• Respond to LINEAR motion

Question 3

What are the semicircular canals? What is the function of the semicircular canals?

Answer 3

• Vestibular organ containing hair cells that respond to ANGULAR acceleration
• Endolymph actually bends the stereocilia

Question 4

What is the vestibular hair cell? What is the function of the vestibular hair cell?

Answer 4

• These are the sensory receptors of the vestibular system
• DEPOLARIZES when stereocilia bent TOWARD kinocilium
• HYPERPOLARIZES when stereo cilica bent AWAY

Question 5

What is endolymph? What is the function of endolymph?

Answer 5

This is the fluid that fills the vestibular division of the membranous labyrinth

Question 6

What is the vestibulo-ocular reflex in response to head tilt?

Answer 6

If the head is tilted to one side, the eyes rotate in the OPPOSITE direction

**This helps maintain the visual field in the horizontal plane

Question 7

What is the vestibulo-ocular reflex in response to head turn?

Answer 7

If the head makes a small turn one direction, eyes turn the OPPOSITE direction

**This facilitates fixation on a distant target

Question 8

What is post rotatory nystagmus. Explain why a patient shows post-rotatory nystagmus.

Answer 8

• Involuntary rhythmic oscillation of the eyes is called post-rotary nystagmus AFTER a patient stops spinning
• Inertia of the endolymph in the semicricular canal makes person think they are turning in the direction OPPOSITE to their initial turning

Question 9

What is the “slow phase of (vestibular) nystagmus?”

Answer 9

Slow phase is the eye movement OPPOSITE to the direction of turning

*Think of the person trying to maintain gaze

Question 10

What is the “fast phase of nystagmus?”

Answer 10

Fast phase is a rapid movement of the eyes back to midline after the slow phase

*Think of the eyes as “jumping ahead”

Question 11

If a patient is in a coma can they exhibit both phases of nystagmus?

Answer 11

NO–they can have the slow phase, but not the fast phase

**Note that the mnemonic gives you the direction of the FAST phase, the slow phase (seen in comatose patient) will be OPPOSITE of the mnemonic for caloric testing

Question 12

What are the directions for nystagmus during turning? After rotation?

Answer 12

During rotation=

• Slow= opposite
• Fast= same

Post rotation= person thinks he/she is turning opposite direction

• Slow= same
• Fast= opposite

*Note that nystagmus is named after the fast component of nystagmus

Question 13

What is the probable cause of positional vertigo?

Answer 13

• Free-floating particles in the semicircular canals
• Specifically, part of an otoconium (Calcium carboante) that is detached from the utricle
• Detachment is caused by trauma or viral labyrinthitis

Question 14

What are the symptoms of positional vertigo?

Answer 14

Episodic vertigo lasting ~40 seconds in different positions

Question 15

What is the probable cause of Meniere syndrome?

Answer 15

Imbalance between the production and reabsorption of endolymph

Question 16

What are the symptoms of Meniere Syndrome?

Answer 16

• Ear fullness/ pressure
• Decreased hearing
• Tinnitus
• Severe vertigo
• Nausea
• Vomiting

**Episodic attacks last minutes to hours at a time

Question 17

Outline the vestibular pathway. What are the main inputs to the vestibular nuclei?

Answer 17

1) Some vestibular hair cells, terminate in vestibular nuclei in the MEDULLA
- Medial & superior nuclei= semicircular canals
- Lateral nucleus= utricle
- Inferior nucleus= utricle, saccule, & semicircular canals

2) Others project to the floculonodular lobe of cerebellum & then the cerebellum projects to vestibular nuclei

Question 18

What are the main outputs of the vestibular nuclei? Assign a function to each output

Answer 18

1) Medial & superior vestibular nuclei synapse via the Medial Fongitudinal Fasciculus (MLF) to the extraocular muscles of the eye
2) Lateral vestibulospinal tract projects to motor neurons of limb & trunk (balance/ posture)
3) Medial vestibulospinal tract–neck muscles–>head position
4) Higher centers (thalamus & cortex)= awareness of body orientation & motion

Question 19

What are the three major roles for the vestibular system? What sensory systems help the vestibular system fulfill these roles?

Answer 19

1) Awareness of body position in space
2) Postural tone & equilibrium
3) Stabilization of the eyes during head movement

Question 20

What is the the doll’s eye maneuver. When is it performed? What is being tested?

Answer 20

• This is a maneuver to evaluate brainstem function in an unconscious patient
• Hold eyes open and tilt head
• See SLOW phase OPPOSITE the direction of head turn

Question 21

What is caloric testing of vestibular function? Describe the set-up for caloric testing of vestibular function.

Answer 21

• This is a test of vestibular function w/out turning the patient
• Cold or warm water irrigated in the ear can cause movement of the endolymph in semicircular canals via convection

Question 22

In caloric testing of vestibular function, how do the eyes move if cold water is put in the ear canal? How do they move in response to warm water? What kind of eye movements would you see in a comatose patient?

Answer 22

COWS–mnemonic to name the FAST phase of nystagmus

Cold= opposite 
Warm= same

Question 23

If a patient is tested by turning to the left, what direction does he or she think they are turning after rotation?

Answer 23

RIGHT

Question 24

After turning a patient to the left, what direction is slow phase post-rotary nystagmus?

Answer 24

Left

*****Mnemonic for post-rotary nystagmus: after turning, SLOW phase is in the SAME direction as turning

Question 25

After turning a patient to the left what direction is fast phase post-rotary nystagmus?

Answer 25

Right

**The fast phase is always opposite of the previous turning movement

Question 26

How is nystagmus named?

Answer 26

Direction of the fast phase