Inner Ear Assessment - Fitz

Question 1

What are vestibulospinal reflexes used for?

Answer 1

coordinating the position of the head and body while maintaining the head in an upright position during movement

Question 2

Compare the lateral and medial vestibulospinal tracts:

Answer 2

Afferent source:
Lat = entire labrynth
Med = only semicircular canals

Function:
Lat = Postural changes to compensate for body movement
Med = stabilize head position during walking

Efferent connection:
Lat = ipsilateral (excitatory)
Med = bilateral (excitatory and inhibitory)

Question 3

What is the vestibulo-ocular reflex’s importance in the clinic?

Answer 3

Dolls eyes
If you don’t have doll’s eyes, this is one of the signs of brain death (Obviously not always true)

In normal people, you should be abel to adjust eyes position to compensate for head motion

Question 4

Explain as simple as possible the pathway for the vestibular-ocular reflex.
Turning your head to the left!
Go! You can do it!

(this thing is so awesome)

Answer 4

Left turn causes a depol to the left and hyperpol to the right semicircular canal.
The left depol excites the left vestibular nucleus
Right hyperpol inhibits right vst nucleus

The left vest nucleus excites inputs to the left occulomotor nucleus and right abducens nucleus to excite the left medial rectus and right lateral rectus

Inhbition will occur oppositely to inhibit the left lateral rectus and right medial rectus

So both eyes look to the right!
(opposite the direction the head turned)

Question 5

What is nystagmus?

Answer 5

Can be provoked in normal person be spinning fast with a sudden stop. Without provocation, it is pathological

It is a slow eye drift (pursuit) followed by rapid compensation in opposite direction (saccade)

Pursuit controlled by the vestibular-ocular reflex
Saccade controlled by cortex

Question 6

Caloric test to measure brain function.

Pouring cool water in the left ear of:
Normal individual
Comatose individual
Brain dead individual

Answer 6

Normal - rightward nystagmus

Comatose - Nystagmus absent

Brain dead - both saccade/pursuit absent

Question 7

Caloric test to measure brain function.

Pouring warm water in the left ear of:
Normal individual
Comatose individual
Brain dead individual

Answer 7

Normal - leftward nystagmus

Comatose - eye drift with no nystagmus

Brain dead - both saccade/pursuit absent