Control of Eye Movements

Question 1

What is a saccadic eye movement?

Answer 1

where the fovea shifts rapidly from one target to another

Question 2

What is a smooth pursuit eye movement?

Answer 2

where the eyes follow a moving image to keep it centred on the fovea

Question 3

What is a vergence eye movement?

Answer 3

moves eyes in opposite directions

Question 4

What is a vestibular ocular eye movement?

Answer 4

hold image still on retina during brief head movements

Question 5

What is an optokinetic eye movement?

Answer 5

holds image stationary during sustained head rotation or translation

Question 6

What are the 6 extraocular muscles?

Answer 6

lateral rectus, medial rectus, superior rectus, inferior rectus, superior oblique, inferior oblique

Question 7

What muscle is tested with abduction and elevation?

Answer 7

superior rectus

Question 8

What muscle is tested with abduction and depression?

Answer 8

inferior rectus

Question 9

What muscle is tested with adduction and elevation?

Answer 9

inferior oblique

Question 10

What muscle is tested with adduction and depression?

Answer 10

superior oblique

Question 11

What muscle is tested with abduction?

Answer 11

lateral rectus

Question 12

What muscle is tested with adduction?

Answer 12

medial rectus

Question 13

What neurons are involved in eye movement?

Answer 13

lower motor neurons (cranial nerves), reticular formation in the brainstem and frontal eye fields in the cortex

Question 14

Which cranial nerve innervates contralateral muscles?

Answer 14

trochlear nerve (IV)

Question 15

What is the medial longitudinal fasciculus?

Answer 15

a white matter tract in the brainstem connecting cranial nerve nuclei

Question 16

What is the pontine paramedian reticular formation?

Answer 16

the horizontal gaze centre

Question 17

What is the mesencephalic paramedic reticular formation?

Answer 17

the vertical gaze centre

Question 18

What are the two types of neurons in the pontine paramedian reticular formation?

Answer 18

burst neurons which fire at high frequency just before an eye movement and omnipause neurons which fire continuously except when there is an eye movement

Question 19

Describe the neural control of a saccade

Answer 19

Higher cortical centres signal to burst neurons in the PPRF. Excitatory burst neurons excite the ipsilateral abducens nucleus. Inhibitory burst neurons inhibit the ipsilateral abducens nucleus. The abducens nucleus signals via the MLF to the contralateral oculomotor nucleus. This results in simultaneous contraction of the lateral and medial rectus as well as inhibition of the opposing lateral and medial rectus muscles.

Question 20

What is internuclear opthalmaplegia?

Answer 20

a defect in the MLF (usually in MS) which means that horizontal eye movements can’t be coordinated

Question 21

Describe the vestibulo-ocular reflex

Answer 21

Movement of the head to the left causes the left semicircular canal to excite the left vestibular nucleus. The left vestibular nucleus will send an inhibitory signal to the left abducens nucleus and an excitatory signal to the right abducens nucleus. The abducens nucleus signals via the MLF to the contralateral oculomotor nucleus. This results in simultaneous contraction of the lateral and medial rectus as well as inhibition of the opposing lateral and medial rectus muscles.