Smooth Pursuit & Vergence

Question 1

What do higher control centres do (in regards to eye movements)?

Answer 1

• Initiate eye movements for different purposes & improve their coordination and accuracy
• Send Motor Commands to the:

Brainstem Generator Nuclei

[Which Generate specific burst patterns of activity & deliver these to Ocular Motor Neurons via axons in the Inter-Nuclear Pathways (MLF)]

Question 2

Which structure in the midbrain is ONLY concerned with smooth pursuit movements?

Answer 2

The Accessory Optic Nuclei

Question 3

Is smooth pursuit voluntary or involuntary?

Answer 3

Voluntary

Question 4

What is the brainstem generator used for smooth pursuit?

Answer 4

Medial Vestibular Nucleus

Question 5

True or False- The medial vestibular Nucleus is the slow conjugate eye movement generator for both voluntary and involunatry eye movements

Answer 5

True

Question 6

How does the Medial Vestibular Nucleus (MVN) cause eye movements?

Answer 6

Burst cells in the MVN send action potentials and have axons that travel through the MLF to the particular cranial nerve that needs to be innervated e.g. to look to the right for the right eye, the lateral rectus and so abducens nerve would be innverated.

This nerve would have axons that innervate muscles of that nerve and then the synergist (i.e. the other nerve (so in this case oculomotor nerve) needed to innervate a particular muscle, e.g. MR in left eye).

Question 7

First and foremost in order to percieve moving images what pathway/process needs to occur?

Answer 7

To percieve moving images, retinal image motion needs to be processed via the:

• Magnocellular pathways to Dorsal Stream Extra-striate Cortex (areas V5/MT & MST)
• Neurons in these areas have large Receptive Fields which pick up on the speed & direction (velocity) of targets as they move across the visual field (i.e., in the fronto-parallel plane)
• & Relay this info to the Parietal Eye Field, where motor commands for tracking are mainly initiated

Question 8

How does damage to V5/MT and/or MST affect smooth pursuit?

Answer 8

Damage to the motion areas V5/MT &/or MST prevents the initiation of smooth pursuit - if you can’t see object motion you can’t track the moving object!

Question 9

What is the pathway of the motor commands being issued from the Parietal Eye field in for smooth pursuit to occur?

Answer 9

Motor Commands Issued from

•PEF (+ some from V5/MT & MST)

Are sent via Descending Motor Pathway

• To Dorsal Lateral Pontine Nuclei (DLPN) then …
• To the Cerebellar Cortex (mainly the Flocculus) then..
• To the Deep Nuclei (mainly the Fastigial nucleus )
• & then to the Brainstem Generator for Slow, Conjugate Gaze = Medial Vestibular Nucleus

Question 10

Where is the PEF (Parietal Eye Field) located?

Answer 10

In the intra-parietal lobe