Chapter 15 Vestibulo-Ocular Response

Question 1

C15

Which parts of the inner ear are important for the translational vestibule-ocular response?

Answer 1

• semicircular canals
• utricle and saccule
• vestibule
• cochlea

Question 2

C15

Which canals in each ear are functionally paired? Are these canals parallel to each other or perpendicular to each other?

Answer 2

Right Ear Left Ear Orientation

• lateral -lateral -parallel
• anterior -posterior -parallel
• posterior -anterior -parallel

Motion Excited Inhibited
-right yaw -right lateral -left lateral
-down head pitch -right anterior -left posterior
(rightward roll)
-down head pitch -left anterior -right posterior
(leftward roll)

Question 3

C15

You want Breanna to hold her head so that the lateral semicircular canals are horizontal in space. Please draw a picture of a way she could do this. The posture you ask her to hold should not be uncomfortable.

Answer 3

Hey Breanna, tip your head down 30 degrees, sort of like you’re tipping your head to look over the top of your sunglasses.

(see picture)

Question 4

C15

Describe the input to and output of the semicircular canals hair cells.

Answer 4

Hair cells respond to forces along their plane of polarization but not forces perpendicular to that plane.

Input to the system in angular acceleration of the head

Output of the hair cells in related more to angular velocity if the rotation does not last too long

Question 5

C15

Make head rotations that (a) excited and (b) inhibit the hair cells in the christae of the right anterior semicircular canal.

Answer 5

(a) excites: downward head pitch, rightward roll

(b) inhibits: upward head pitch, leftward roll

Question 6

C15

Janet reclines on her back on a bed with a pillow so that her lateral semicircular canal is vertical in space (Figure 15.5.). She quickly turns (yaws) her head to her right shoulder. Which semicircular canal will produce the largest excitatory signal?

Answer 6

right lateral canal

Question 7

C15

What is the role of the vestibulo-ocular response in Schor’s functional category system?

Answer 7

Stabilization of gave for the environment despite head movements

Question 8

C15

Name a typical daily activity where the rotational vestibule-ocular response in important for vision. Explain why it is important.

Answer 8

• maintaining balance (on a boat)

- important because it stabilizes vision

Question 9

C15

To which temporal frequencies of head motion does the rotational vestibule-ocular system respond best? How would you describe the passband of this system?

Answer 9

• responds best to high temporal frequencies of head rotation
• a high pass system

(vestibulo-ocular response responds best to brief head rotations and is not well adapted to sustained rotation of the head)

Question 10

C15

Heather sits on a Barany chair. (We used this chair in the first lab class.) Her seatbelt is fastened. She is turned clockwise at a constant angular speed for 5 minutes. The chair is then stopped abruptly. In which directions will the slow and fast phases of her post-rotatory nystagmus go? Explain your answer.

Answer 10

post-rotatory nystagmus: observed when angular velocity changes after a long period of rotation at a constant angular velocity

• slow phase eye movements to the right
• fast phase eye movements to the left
• the halt will stimulate acceleration in the opposite direction to the original constant velocity motion
• after time (5 minutes) her endolymph will be traveling in a clockwise motion, and it will place forces on the cupola to the left, simulation a leftward head movement

Question 11

C15

Draw diagrams to show how (a) positive and (b) negative spectacles lenses alter the necessary vestibulo-ocular gain for viewing a distant target with head rotation.

Answer 11

(a) positive spectacle: eyes undershoot until they can accommodate, hyperopic eyes need vestibulo-ocular response gain >1.0 (see picture)
(b) negative spectacle: eyes overshoot until they can accommodate, myopic eyes need vestibulo-ocular response gain of <1.0 (see picture)

Question 12

C15

Jose has spectacle lens powers of +3.00 DS in right and left eyes. He normally wears spectacles, but decides to wear contact lenses today. What chance in vestibulo-ocular gain is required, and why?

Answer 12

• Jose is a hyperopia and requires a vestibulo-ocular gain of GREATER than 1.0 to accommodate with his glasses on (more eye turn than head turn since he undershoots with his plus lenses)
• Once he puts his contacts on, he will need to DECREASE his gain back to 1.0 (eye rotation = head rotation) but can’t have a gain less than 1.0)

Gain = eye rotation / head rotation

-prismatic effects are not important in the case of contact lens wear, because contact lenses generally move with the eye… even if they don’t move with the eye the distance of the line of sight from the optical center of the lens (c) is much smaller than with spectacle lenses

Question 13

C15

Which neural area assists to adjust the vestibulo-ocular response timing to obtain a more accurate response?

Answer 13

flocculus of the cerebellum

Question 14

C15

Which types of motions are better for the vestibulo-ocular system, and which types of motions are better for the optokinetic system? In your answer, take care to note the differences between bead motion stimuli and optic flow stimuli, and to use them appropriately.

Answer 14

• vestibulo-ocular responds better to fast, brief head rotations
• optokinetic responds better to ow temporal frequencies of optic flow and slow sustained optic flow
• the vestibulo-ocular response and the optokinetic response complement each other

Question 15

C15

What purpose does the otolithic counter-roll serve in humans?

Answer 15

Otolithic counter-roll maintains stable gaze for the environment despite head rotations

*it is NOT a very important system in humans

Question 16

C15

Using your knowledge of semicircular canal physiology, and with reference to Figure 15.18: (a) Explain why the pathways of those diagrams are appropriate for a rightward head yaw, noting the flow of information from head motion, to semicircular canal, to yoke muscles in the two eyes; (b) Give an example of Sherrington’s Law in those diagrams; (c) Give an example of Hering’s Law in those diagrams.

Answer 16

Receptor
-lateral canal excitatory iMR cLR
inhibitory iLR cMR
-anterior canal excitatory iSR cIO
inhibitory iIR cSO
-posterior canal excitatory iSO cIR
inhibitory iIO cSR

Question 17

C15

Johnathon’s vestibulo-ocular response are tested with caloric stimulation. He lies supine with his head pitched by 30 degrees so that the lateral canals are vertical (Figure 15.5). His left ear is irrigated with warm water. Draw a diagram(s) to show the reasoning behind your reduction of the direction of the slow and fast phases of the nystagmus. Does your explanation support the ‘COWS’ mnemonic?

Answer 17

X = left or right

• warmth in X ear causes upward vection currents that simulate Xward head motion, this is excitatory for the X later canal
• fast-phase eye movement (saccade) is observed to the X
• slow-phase eye movement is observed in the opposite direction of X
• cold is opposit of warm
• COWS: Cold Other, Warm Same

In regards to Johnathon, because his left ear is being irrigated with warm water, there will be upward vector currents that simulate leftward head motion, this is excitatory for the left later canal. His fast-phase eye movement will be observed to the left. His slow-phase eye movement will be observed to the right.

Question 18

C15

Use left and right origami semicircular canals to show the correct orientation of the canals when the head is in the erect position.

Answer 18

LAP

later canal - 30 degrees
anterior canal - 150 degrees
posterior canal - 270 degrees

Question 19

C15

Why is vision needed for good vestibulo-ocular responses? How does the presence of this negative feedback fit with my initial (simplified) class explanation of the rotational vestibulo-oculer response as a feed-forward system?

Answer 19

IDK