Lab 3 - Oculomotor Muscle Control

Question 1

What is the objective of lab 3?

Answer 1

to measure and investigate the activity of the medial and lateral rectus muscles during eye movement

Question 1

describe the muscles of the eye

Answer 1

• 6 exterior muscles (3 antagonistic) pairs control horizontal, vertical, and torsional movement/position of the eye
• vertical axis:
  adduction (towards the nose): medial rectus muscle
  abduction (away from the nose): lateral
• horizontal axis:
  elevation (towards the sky) and intorsion (slightly towards the nose): superior rectus
  depression (towards the ground)
  and extorsion (slightly away from the nose): inferior rectus
  -torsional axis:
  intorts: superior oblique muscle
  extorts: inferior oblique
  -innervated by motor neurons:
  position of the eye: under tonic control
  velocity of movement: phasic control

Question 2

what are the 5 types of eye movement?

Answer 2

• saccades
• pursuit
• vestibular
• ocular reflex
• vergence

Question 3

describe the functions and properties of the saccades movement. give an example

Answer 3

• rotates the eye so that the image of interest falls on the fovea of the retina
• e.g., to point a the words in a sentence during
  -during movement, vision is poor, so this movement is very fast (velocity: 800 degrees/ second)
  -accuracy controlled by saccadic system. neural integrator internally estimates the eye position to guide and stop the saccades

Question 4

describe the functions and properties of the vestibular ocular reflex (VOR) movement

Answer 4

• keeps the eye still while the head moves
  -phasic response
• faster than phasic because simple central reflex arc involving only 3 neurons
• semicircular canals of the ear detect movement and send signal to afferent nerve to interneuron to ocular muscle
• muscle velocity rotates the eye at the same velocity of the hear, keeping the image stable
• eyes held on image through tonically controlled neural circuit

Question 5

describe the functions and properties of the optokinetic reflex movement

Answer 5

• active when a full field of vision has moved across a large portion of the retina
  -slower than VOR but better for slow and prolonged movement
  -tested by displaying rotating images on the walls of a small circular room (optokinetic drum)
  -e.g. occurs when a car next to u moves backwards and gives the sensation that u are moving forward
  NOT TESTED BC MATERIALS TOO COMPLEX

Question 6

describe the functions and properties of the pursuit movement

Answer 6

• keeps the fovea pointed at a moving target
  -e.g, keeping ones eye on a bouncing ball
• initial latency/delay in pursuit because signal from eye that indicates object is moving must be conducted through multiple synapses to the brainstem
  -saccades helps track movement until pursuit catches up

Question 7

describe the functions and properties of the vergence movement

Answer 7

• points the fovea of the eyes on two objects of different distances away (further/closer)
• eyes rotate in opposite directions, unlike saccades
  -eyes converge when looking far to near
  -eyes diverge when looking near to far
  -prevents double vision

Question 8

equipment in lab 3

Answer 8

iWorx kit
laptop
EMG electrodes and wires
ball/object on 5ft of thin string

Question 9

where are the electrodes placed in lab 3

Answer 9

Green (G)round): below the right ear
red (+1): next to the left eye
black (-1): next to the right eye

Question 10

lab 3 E1 (saccades) setup and results

Answer 10

• subject reads a simple 10 line paragraph while EOG is recorded. then a more complex, longer line paragraph. avoid head movement
• EOG reading: step-like increase from word to word on a line. a new line is indicated by a steep drop on the EOG.
  -slower saccadic movement = longer EOG step readings
• eye movement: saccadic/jerk-ey

Question 11

lab 3 E2 (VOR) setup and results

Answer 11

• subject looks at image and roates their head side to side. repeat with faster head movement
• EOG: sinusoidal reading. increased frequency of “waves” during faster head movement
  -eye movement was SMOOTH not saccadic (opp of pursuit)

Question 12

lab 3 E3 (pursuit) setup and results

Answer 12

• suspend ball on string in front of uniform coloured background. swing it from side to side. have the subject track the movement without moving their head. repeat with slower target movement (increase string length).
• EOG: sinusoidal but shaky. slower movement = longer wavelength
• eye movement: SACCADIC not smooth (opp of VOR). slower target= smoother eye movement

Question 13

lab 3 E4 (vergence) setup and results

Answer 13

• two targets of similar size and shape positioned at 3 and 6 ft respectively. subject looks back and forth btw objects for 4 sec intervals. repeat with slower intervals.
  -EOG: square peaks.
  convergence: downward peak/step
  divergence: upward peak/step
  repeats high-low-high-low.
  slower intervals = longer step time
  -eye movement: eyes cross when looking at close object and diverge slightly when looking at farther object. SACCADIC but smoother with longer interval time