NEUROANATOMY - Supranuclear Gaze Pathways

Question 1

What are the originators of vertical saccades? (2)

Answer 1

1. frontal eye fields
2. superior colliculus

Question 2

What is the functional centre for horiontal eye movements / gaze?

Answer 2

The PPRF (paramedian pontine reticular formation)

Question 3

What are the 4 main systems to maintain fast eye movement?

Answer 3

1. Saccades
2. Pursuit
3. Vergence
4. Vestibulo-ocular

Question 4

What is the pathway for horizontal saccades? Where is the horizontal center located?

Answer 4

IN THE PONS.

Frontal eye fields in area 8 of frontal lobe (saccades) + parietal-occipitojunction (pursuit) –> superior colliculus –> CONTRALATERAL PPRF –>
1. ipsilateral 6th nerve nucleus –> ipsilateral LR
2. MLF –> contralateral 3rd nerve nucleus –> contralateral MR

Question 5

What is the pathway of vertical saccades? Where is the vertical center located?

Answer 5

THE THALAMO-MESENCEPHALIC JUNCTION IN THE DORSAL MIDBRAIN

Frontal eye fields & parietal-occipital junction –> superior colliculus —> contralateral RIMLF (rostral interstitial nucleus of medial longitudinal fasciculus) –> interstitial nucleus of cajal –> third nerve subnuclei

Question 6

Why is an upgaze palsy more common than a downgaze palsy?

Answer 6

upgaze pathway is mediated by single posterior commisure, downgaze pathway is bilateral

Question 7

What does the medial longitudinal fasciculus connect?

Answer 7

ipsilateral 6th nerve nucleus in pons to the contralateral 3rd nerve nucleus in the midbrain

Question 8

How can you tell if an INO is a pons lesion or a midbrain lesion?

Answer 8

Convergence test
If able to converge –> 3rd nerve nucleus is still intact in the midbrain –> PONTINE LESION

If not able to converge –> 3rd nerve nucleus is affected –> MIDBRAIN LESION

Question 9

What is the velocity of smooth pursuit movements?
What is the velocity of saccadic movements?

Answer 9

smooth pursuit: 30-50 degrees / second
saccades:
saccadic - 800-1000 degrees / second

Question 10

What is the latency of smooth pursuit movements?
What is the latency of saccadic movements?

Answer 10

smooth pursuit - 150ms
saccades - 100ms

Question 11

Which centre controls saccades?

Which centre controls smooth pursuits?

Answer 11

Saccades: Contralateral frontal eye field
Pursuit: Ipsilateral parietal area