Eye Movement Control Systems Flashcards
Control System
A mechanical, optical, or electronic system that is used to maintain a desired output
Open loop system
no feedback; input/stimulus/control signal goes through the system and results in an output/response/controlled variable
T/F an open loop system only has one step
False, can be multistep
Do biological systems usually use an open or closed loop system?
closed
Closed loop system
start with goal/desired output –> control decision –> final control element –> process –> output –> sensor –> measured output (Compared to desired output)
Idea of movement
William James’ closed loop system; sensory cell excitation triggers kinesthetic and motor neuron at the same time which provides closed loop feedback allowing the body to compare anticipation and reality
What are the three components of the idea of movement?
M= motor neuron; K=kinesthetic neuron “plan signal” aka what to expect; S = sensory cell
Signal types
pulse, step, ramp
Pulse signal
Responsible for getting eye movement started; needs to overcome viscosity (and elasticity?)
Viscosity
Fat holding the eye still; overcome by pulse signal
Elasticity
Wants to keep the eye in primary gaze; overcome by step signal
Step signal
Keeps eye in eccentric position so it doesn’t move back to center; overcomes elasticity and fights against centripetal force
How are pulse and step signals depicted on a graph?
Pulse are vertical lines w/ an amplitude, step are horizontal lines w/ width
Ramp signal
Slow increase in signal NOT on/off, like NPC; diagonal line on a graph
Neural integrator
Neural networks that receive input signals and generate appropriate output signals; may have input from multiple areas; combined with calculus we ain’t gonna do
T/F there’s one kind of neural integrator
False- separate neural integrators exist for each type of eye movement
Example of neural integrator
Superior colliculus
Two types of neural integrators
Perfect and leaky
Perfect Neural Integrator
Input gives constant output; no decay to the signal overtime; eye movements are not perfect integrators
Leaky Neural Integrator
Signal decay= output decay
Feedback theories: How do we know where our eyes are in our head?
Proprioception from EOM tendons and/or efferent plan signals
Feedback theories: How do we know where our head is on our torso?
Proprioception in the supporting muscles of the neck and upper back (functional origin of EOMs) or afferent fibers from the cervical ganglion give finer detail
Mesenchymal tissue
most prevalent early– infant development
Myoblast cells
precursors to the different types of muscle tissue that develop in the extraocular muscles
How does myoblast differentiation take place?
Innervation during development guides the emergence of which type of cell to develop into
What age is the cut off for myoblasts?
8-9 years old
Mature muscle fibers
Fibrillen and Felder
Fibrillen fibers
80% of fibers, for saccades, fast twitch, fast fatigue, large diameter, peripheral nuclei, abundant sarcoplasm, single motor endplate
Felder fibers
20%, for sustained convergence at near, slow twitch, slow fatigue, tonic, small diameter, some central nuclei, little sarcoplasm, local terminals
What happens with too few Felder fibers?
Convergence problem and inability to sustain at near
Are muscle fibers continuous or broken?
Broken by 18 months old, as shown by proprioception spindles in EOMs– makes positional info not super accurate
What is the effect of breaks in muscle fiber?
Doesn’t allow accurate reporting of total degree of stretch; difficult to know where eyes are based on fibers
What is the summary of Bruenech’s research?
Proprioception does not have a large role in eye position monitoring– only in infants before muscle breaks
T/F There are stretch receptors in EOM tendons
False, stretch receptors are absent; different than tendons in the rest of the body
T/F Myotendinous nerve endings are present during binocular visual development
False, they are not present aka we do not know where our eyes are in our head based on proprioception
Efferent copy of position signal
loops back to perceptual like kinesthetic neuron
Saccadic neuron types
pause, burst, burst-tonic, tonic, motor
Pause saccadic neuron
constantly firing at a low rate to keep eye relatively still, must stop this signal in order to get a movement
Burst saccadic neuron
takes care of the pulse signal– short and fast signal to get over viscosity and start the movement
Burst-tonic saccadic neuron
some low level signal, includes short burst to help with start (some pulse, some step)
Tonic saccadic neuron
low-level signal that continues but higher intensity in the new position to keep the eye there (step)
Motor saccadic neuron
the actual MOVE signal, slow at rest then faster as eye moves, slow when eye reaches new position and lets tonic help out (accounts for drift and refixation)
Saccadic generation
signal sent from superior colliculus (neural integrator) –> long-lead burst and omnipause neurons –> excitatory burst neurons –> motor neurons
What is inhibitions role in saccade generation?
input from inhibitory burst neurons and connections made thru interneurons and tonic neurons
What is the ratio for EOM innervation?
1:1
What is a ventral stream?
Form related brain areas that runs along the sides of the head– “what”
What is a dorsal stream?
Motion related brain areas that run up top from back of head– “where”
T/F There is overlap between the ventral and dorsal stream
true
What are the two excitatory burst nerve centers?
EBNH (brainstem for horizontal movements) and EBNV (reticular formation of the mesencephalon for vertical eye movements
What do EBNs do?
jump-start; discharge in EBNs is 10-15 msec before the saccade itself– injury can affect just horizontal or just vertical
How does pursuit control work?
gets input back and forth from FEF aka impulse control
