Week 3 - Ach (Gaze Systems)

Question 1

What are saccadic movements?

Answer 1

• Rapid/jerky eye movements
• Bring image of a new object onto the fovea
• Allow us to quickly scan points on an image (eyes on a new face)

Question 2

What are smooth pursuit eye movements?

Answer 2

• Eye movements that keep a moving image centered on the fovea
• Tracking

Question 3

What does the Vestibulo-ocular gaze do?

Answer 3

Keeps an image steady on the fovea during head movements.

Question 4

What is vergence?

Answer 4

Eye movements that keep an image on the fovea when the viewed object is moved near –> far.

Question 5

Describe the Saccadic Gaze System.

(7 steps, give or take one or two)

Answer 5

1. Signal comes in from visual field, retina, auditory, somatosensory system.
2. Superior colliculus sends axon to
3. Lateral Gaze Center (PPRF) –> sends two axons to
4. Abducens Nucleus –> sends one axon to Lateral rectus musce & one axon to
5. Medial longitudinal fasciculus –>
6. Oculomotor Nucleus in midbrain –> sends axon to
7. Medial Rectus muscle

Question 6

What does PPRF stand for?

Answer 6

Paramedian Pontine Reticular Formation

-area in midbrain that initiates saccaidic gaze system

Question 7

What classic skill is due to smooth pursuit eye movements?

Answer 7

Eye-Hand Coordination

Question 8

How does the initiation of smooth pursuit eye movements begin?

(4 steps)

Answer 8

1. See moving object
2. Message from Optic Nerve
3. Message received by Frontal cortex
4. Signal travels to Superior Colliculus & several Pontine Nuclei

Question 9

Name the 5-6 major stops in the Vestibulo-ocular reflex.

Answer 9

1. Left horizontal semicircular canal
2. Vestibular nucleus
3. Abducens nucleus
4. Lateral Rectus (right)
5. Oculomotor nucleus (via internucleus neuron from Abducens nucleus traveling along MLF)
6. Medial rectus (left)

Question 10

What does convergence mean in terms of the pupils?

Answer 10

Interpupillary distance DECREASES.

Question 11

What eye muscles does convergence require contraction and relaxation of?

Answer 11

Contraction: both Medial recti muscles

Relaxation: both Lateral recti muscles

Question 12

What is Divergence?

Answer 12

A voluntary abduction of both eyes to primary position.

Question 13

What is the position of the eyes if a lesion in the Right Abducens Nerve (CN VI) is present?

Answer 13

​Right Abducens (CN VI) Nerve Palsy:

• Leftward gaze unaffected.
• Rightward gaze
  
  • Right eye straight
  • Left eye inward at nose

Question 14

What is the position of the eyes if a lesion of the Abducens nucleus was present?

Answer 14

Right Lateral Gaze Palsy:

• Leftward gaze unaffected.
• Rightward gaze:
  
  • Both eyes straight forward
  • (no saccadic movements to the right)

Question 15

What is the position of the eyes if a lesion of the right Paramedian pontine reticular formation (PPRF) was present?

Answer 15

Right Lateral Gaze Palsy:

• Leftward Gaze unaffected.
• Rightward Gaze:
  
  • Eyes straight forward.
  • (no saccadic movements to the right)

Question 16

What is the position of the eyes if a lesion of the Medial Longitudinal Fasciculus (MLF or interneuron) was present?

Answer 16

Left INO

• Leftward gaze unaffected.
• Rightward gaze:
  
  • Right eye abducted (rightbeating nystagmus?).
  • Left eye straight forward.

Question 17

What is the position of the eyes if a lesion of the Left Medial Longitudinal Fasciculus (MLF) and Left Abducens Nucleus?

Answer 17

Left MLF and Left Abucens nucleus (1 1/2 Syndrome):

• Leftward gaze unaffected.
• Rightward gaze:
  
  • Right eye abducted (rightbeating nystagmus?)
  • Left eye straight forward.