Brainstem and oculomotor

Question 1

The GSE nuclei of the brainstem

Answer 1

Comprised of CN III, IV, VI, and XII
(XI actually in upper cervical cord)
Paired organs, muscles
Conjugate and vergence movements
Works like the corticobulbar system (pre-motor…upper motor…lower motor… effector), although NO cotricobulbar fibers
All in dorsomedial region
Basal Plate derivatives
Contain cell bodies of lower motor neurons

Question 2

Cranial nerve nuclei also follow

Answer 2

Bell-Magendie Law

oculomotor stuff is going to be in the center of the brainstem

Question 3

Different neural circuits control different types of eye movements.

Answer 3

All involve coordination between the ocular GSE cranial nerve nuclei

Question 4

Nystagmus

Answer 4

(Drifting): Rhythmic, involuntary eye movements (may be fast or slow)

Vestibulo ocular reflex: Movement of the eyes to compensate for movement of the head

Optokinetic reflex: Nystagmus during movement of visual stimuli across the retina
Eyes following scenery through a train window (then ping back)

Question 5

Saccades:

Answer 5

Rapid, ballistic eye movements to move image into the fovea (may be voluntary or involuntary)

center the image.

Question 6

Smooth movement pursuits:

Answer 6

Smooth, voluntary, slow, tracking movements on a moving target

Question 7

Control of eye movements serves to

Answer 7

shift gaze or direct image to fovea

Question 8

Oculomotor nerve (III) also innervates

Answer 8

the superior rectus, inferior and medial recti and the inferior oblique

Question 9

Trochlear nerve (IV) innervates

Answer 9

the superior oblique

Question 10

The abducens nerve (VI)

Answer 10

innervates the lateral rectus

Question 11

The medial longitudnal fasciculus

Answer 11

connects the cranial nerves and integrates movements directed by gaze. It is a bundle of axons composed of ascending and descending fibers arising mainly from the medial vestibular nucleus. Ascending fibers travel ipsilaterally and connect cranial nerve nuclei that innervate extra-ocular muscles (III, IV, VI).

Question 12

Vestibulo ocular reflex (VOR):

Answer 12

A simple illustration of the MLF

Horizontal movement of head activates the medial longitudinal fasciculus (MLF)

Rule of thumb:
Head moves to the right, eyes move to the left

Scarpa’s Ganglion (decussates)–> abducens nucleus (lateral rectus) –> (decussates) contralateral oculomotor nucleus (medial rectus)

(The VOR also affects gaze in the upward/downward direction, uses the MLF across superior rectus, superior oblique and inferior oblique)

Question 13

The superior colliculus and PPRF are the two major areas controlling the MLF

Answer 13

There are retinotoptic maps in the superior colliculus as well similar maps for auditory, somatosensory systems

Superior colliculus through the PPRF (paramedian pontine reticular formation) to orient eyes toward visual stimulus
PPRF is a relay in the MLF
Innervates abducens nucleus

The Frontal Eye Fields (BA 8) activate the superior colliculus contralaterally, allowing for “voluntary” saccades
Parietal eye fields control “reflexive” saccades

Question 14

what is the only cranial nerve that exits from the dorsal side of the brainstem?

Answer 14

trochlear

Question 15

what can we not do saccades without?

Answer 15

superior colliculus

a place where we are orienting toward sounds, visual, touch stimuli.

Question 16

Pathways to voluntarily/involuntarily control saccades

Answer 16

Frontal eye fields (FEF): Intentional saccades [Area 8]

Parietal eye fields (PEF): Reflexive saccades [angular/supramarginal gyrus]

Dorsolateral prefrontal cortex (DLPFC): Inhibiting saccades

Question 17

omnipause neurons

Answer 17

RIP (OPN)

in the pontine raphe nuclei
keep the eyes from moving

tonically releasing glycine

Question 18

superior colliculus and the omnipause neurons

Answer 18

superior colliculus, acting through the MRF, will disinhibit the PPRF from the omnipause neurons.