Lecture 16 - Occulomotor Systems Flashcards
What are the two main reseaons we move our eyes? [2]
- To look at something
- To track something
What are the five types of eye movement? [5]
- Saccades
- Smooth pursuit movements
- Vergence eye movements
- Vestibulo-ocular movements
- Optokinetic movements
What are saccades?
Shifting the fovea to a peripheral target
What are Smooth pursuit movements?
Keeping the images of a moving target on the fovea
What are Vergence eye movements?
Moving the eyes in opposite directions so an image is on both foveae
What are Vestibulo-ocular movements?
- Keeps image on retina during brief head movements
- Driven by the vestibular system
What are Optokinetic movements?
- Keeps image on fovea during sustained head movements
- Driven by visual stimulation
Saccades are very […].
Fast
What can we change about a saccade?
- Direction
- Aplitude
What direction does Abduction rotate the eye?
Away from the nose
Which direction does Adduction rotate the eye?
Towards the nose
Which direction does Elevation rotate the eye?
Vetically up
Which direction does Depression rotate the eye?
Veritcally down
Which direction does Intorsion rotate the eye?
Rotates top of cornea towards the nose
Which direction does Extorsion rotate the eye?
Rotates top of cornea away from the nose
What are the six muscles that move the eye? [6]
- Superior rectus
- Inferior rectus
- Medial rectus
- Lateral rectus
- Superior oblique
- Inferior oblique
Which muscle is responsible for adduction of the eye?
Medial rectus
Which muscle is responsible for abduction of the eye?
Lateral rectus
What happens to individuals with lesion on extraocular muscles/nerves?
- Suffer double vision
- Image is no longer on the same point of both fovea
What are the three cranial nerves that control the extraocular muscles? [3]
- The abducens nerve (CN VI)
- The occulomotor nerve (CN III)
- The trochlear nerve (CN IV)
What is the relationship between eye velocity and extraocular motor neuron firing rate?
As the velocity increases the firing rate also increases
What happens once the eye has reached its desired position?
It is held in place by contraction of the extraocular muscles
Where do the motor circuits for saccades reside?
In the brain stem
Where is the horizontal component of a saccade located?
In the pons and meddula
Where is the vertical component of the saccade loacted?
In the mesencaphaluc reticular formation (in midbrain)
What does the pulse part of the step-pulse signal show?
The speed of the saccade
What does the step part of the step-pulse signal show?
The extent of the saccade
Whcih neurons give rise to the pulse component?
Burst cells
What is the role for medium-lead burst cells?
Making direct conections to the motor neurons
What is the role for long-lead burst cells?
- Driving medium-lead burst cells
- Recieving inputs from higher centres
What is the role for inhibitory burst cells?
- Supressing contralateral abducens neurons and excitatory burst neurons
- Driven by medium-lead burst cells
What is the role for Omnipause cells?
They inhibit burst neurons
How do omnipause cells work?
- Fire continuosly
- Stop firing around the time of a saccade
Which parts of the brain stem is responsible for maintaining a signal relating to eye position? [2]
- Medial vestibular nucleus
- Nucleus prepositus hypoglossi
What are saccades controlled by?
The cerebral cortex
What controls the output for the pontine and mescenphalic burst cells?
The superior colliculus
What are the two function regions of the superior colliculus? [2]
- Superficial layers
- Intermediate & Deep layers
Where do the superficial layers recieve input from?
- Retina
- Primary visual cortex
The activity in neurons of the intermediate and deep layers is related to what?
Occulomotor actions
What affect do the basal ganglia have on the super colliculus?
They send powerful inhibitory signals
What is the role of Frontal eye field neurons?
- They excite movement related neurons in the intermediate layers of the supper colliculus
- Inhibit the inhibitory projection from the basal ganglia
Where are the neurons that are responsible for smooth pursuit located? [3]
- The medial vestibular nucleus
- The nucleus prepositus hypoglossi
- The pons
Which muscles control vergence?
The horizontal rectus muscles
Which neurons control vergence?
Neurons in the occulomotor nucleus of the midbrain
