Eye Movement Control Systems Flashcards
Definition of control system
A mechanical, optical, or electronic system that is used to maintain a desired output.
What is an open loop system?
An open loop system can be 1 step or multi step. It does not have a closure, and does not give feedback. Whatever the output is.. is what you get. Cannot make changes or alter.
Not a great set up for physiological control.
What is a closed loop system?
A closed loop system gives feedback, which is very important in biochemical or neurological processes.
Checkpoints are used to manipulate the output. Once you get the output, it goes through a sensor to determine how close it is to the desired output.
Ex: Oven or thermostat. You want oven to be at 400 degrees. If we are not at 400, then we need to turn power switch on or off to get to the desired output.
What was William James’ “idea of movement”?
When we think about things, conscious thought triggers some type of movement in the body.
When the sensory cell is excited by some stimulus coming in, it triggers the Kinesthetic neuron with a signal that says “Im going to attempt to make a movement to X location.” At the same time, it triggers the motor neuron. Those two signals come in parallel to each other and gives the closed loop system, which is needed to determine if the movement was successful or not.
If our thoughts are able to create movement, there has to be some way for us to determine if we made the correct movement or not.
Sever types of signals exist. What are the 3 major categories?
Pulse, step, and ramp.
What is pulse responsible for?
Getting the eye started. Overcoming the two forces that want to keep the eye in primary gaze: viscosity and elasticity.
Viscosity- Eye is packed in with fat and muscles. Eye is stuck in this and has to exert a lot of energy to rotate.
Elasticity- When eye is turned to an uncomfortable position, tendons have stretch receptors that will pull eye bak to primary gaze. They will resist the action of the step.
What is step responsible for?
Keeps the eye in the eccentric position. (AKA, once the eye is moved by pulse, then step will keep the eye in that new position). Otherwise, it would move back to the center.
What is ramp?
A slow increase in signal, rather than BAM on or off.
Example: NPC. Slow increase in signal as you do a slow motion inward. Slow build up for stimulus to converge eyes.
Neural integrators definition
Neural networks that receive input signals and generate appropriate output signals. May have input from multiple areas.
Types: perfect, leaky
What are perfect and leaky integrators?
Perfect: Input gives a CONSTANT output. No decay happens to the signal over time. When there is a pulse input, the perfect neural integrator will hold the eye at this position and never wavers.
Leaky integrator: What actually happens. The signal, or step, or output, decays over time. Eyes will drift back towards center with extended time in eccentric gaze.
What do factors cause the eyes to move back towards primary gaze?
Leaky integrator. Neurological signal decreases over time. And elasticity. EOMs and their tendons want to pull eye back to center when muscles are stretched.
How do we know where are our eyes are in our head? How do we know where our head is on our torso?
Proprioception in the supporting muscles of the neck and upper back.
Afferent fibers from the cervical ganglion give finer detail about head location on torso.
Development of human somatic muscle fibers
Mesenchymal tissue is the earliest to develop.
End up transforming into myoblast cells.
Then develop into muscle tissues that you see in EOMs.
If we do not get this development, you can have problems later on with ratios of fiber types in EOMs that can cause EOM deficits down the line.
Two types of mature muscle fibers
Fibrillin fibers (80%) for saccades. Fast twitch.
Sustained convergence, Felders fibers (20%) slow twitch
What happens if there is a decrease in the number of felder fibers?
There will be a resultant convergence problem and an inability to sustain at near.
Due to a lack of appropriate developmental experiences, enough myoblasts are not nurtured to become felder fibers.
