Eye Movement Control Systems

Question 1

Control System

Answer 1

A mechanical, optical, or electronic system that is used to maintain a desired output

Question 2

Open loop system

Answer 2

no feedback; input/stimulus/control signal goes through the system and results in an output/response/controlled variable

Question 3

T/F an open loop system only has one step

Answer 3

False, can be multistep

Question 4

Do biological systems usually use an open or closed loop system?

Answer 4

closed

Question 5

Closed loop system

Answer 5

start with goal/desired output –> control decision –> final control element –> process –> output –> sensor –> measured output (Compared to desired output)

Question 6

Idea of movement

Answer 6

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

Question 7

What are the three components of the idea of movement?

Answer 7

M= motor neuron; K=kinesthetic neuron “plan signal” aka what to expect; S = sensory cell

Question 8

Signal types

Answer 8

pulse, step, ramp

Question 9

Pulse signal

Answer 9

Responsible for getting eye movement started; needs to overcome viscosity (and elasticity?)

Question 10

Viscosity

Answer 10

Fat holding the eye still; overcome by pulse signal

Question 11

Elasticity

Answer 11

Wants to keep the eye in primary gaze; overcome by step signal

Question 12

Step signal

Answer 12

Keeps eye in eccentric position so it doesn’t move back to center; overcomes elasticity and fights against centripetal force

Question 13

How are pulse and step signals depicted on a graph?

Answer 13

Pulse are vertical lines w/ an amplitude, step are horizontal lines w/ width

Question 14

Ramp signal

Answer 14

Slow increase in signal NOT on/off, like NPC; diagonal line on a graph

Question 15

Neural integrator

Answer 15

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

Question 16

T/F there’s one kind of neural integrator

Answer 16

False- separate neural integrators exist for each type of eye movement

Question 17

Example of neural integrator

Answer 17

Superior colliculus

Question 18

Two types of neural integrators

Answer 18

Perfect and leaky

Question 19

Perfect Neural Integrator

Answer 19

Input gives constant output; no decay to the signal overtime; eye movements are not perfect integrators

Question 20

Leaky Neural Integrator

Answer 20

Signal decay= output decay

Question 21

Feedback theories: How do we know where our eyes are in our head?

Answer 21

Proprioception from EOM tendons and/or efferent plan signals

Question 22

Feedback theories: How do we know where our head is on our torso?

Answer 22

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

Question 23

Mesenchymal tissue

Answer 23

most prevalent early– infant development

Question 24

Myoblast cells

Answer 24

precursors to the different types of muscle tissue that develop in the extraocular muscles

Question 25

How does myoblast differentiation take place?

Answer 25

Innervation during development guides the emergence of which type of cell to develop into

Question 26

What age is the cut off for myoblasts?

Answer 26

8-9 years old

Question 27

Mature muscle fibers

Answer 27

Fibrillen and Felder

Question 28

Fibrillen fibers

Answer 28

80% of fibers, for saccades, fast twitch, fast fatigue, large diameter, peripheral nuclei, abundant sarcoplasm, single motor endplate

Question 29

Felder fibers

Answer 29

20%, for sustained convergence at near, slow twitch, slow fatigue, tonic, small diameter, some central nuclei, little sarcoplasm, local terminals

Question 30

What happens with too few Felder fibers?

Answer 30

Convergence problem and inability to sustain at near

Question 31

Are muscle fibers continuous or broken?

Answer 31

Broken by 18 months old, as shown by proprioception spindles in EOMs-- makes positional info not super accurate

Question 32

What is the effect of breaks in muscle fiber?

Answer 32

Doesn't allow accurate reporting of total degree of stretch; difficult to know where eyes are based on fibers

Question 33

What is the summary of Bruenech's research?

Answer 33

Proprioception does not have a large role in eye position monitoring-- only in infants before muscle breaks

Question 34

T/F There are stretch receptors in EOM tendons

Answer 34

False, stretch receptors are absent; different than tendons in the rest of the body

Question 35

T/F Myotendinous nerve endings are present during binocular visual development

Answer 35

False, they are not present aka we do not know where our eyes are in our head based on proprioception

Question 36

Efferent copy of position signal

Answer 36

loops back to perceptual like kinesthetic neuron

Question 37

Saccadic neuron types

Answer 37

pause, burst, burst-tonic, tonic, motor

Question 38

Pause saccadic neuron

Answer 38

constantly firing at a low rate to keep eye relatively still, must stop this signal in order to get a movement

Question 39

Burst saccadic neuron

Answer 39

takes care of the pulse signal-- short and fast signal to get over viscosity and start the movement

Question 40

Burst-tonic saccadic neuron

Answer 40

some low level signal, includes short burst to help with start (some pulse, some step)

Question 41

Tonic saccadic neuron

Answer 41

low-level signal that continues but higher intensity in the new position to keep the eye there (step)

Question 42

Motor saccadic neuron

Answer 42

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)

Question 43

Saccadic generation

Answer 43

signal sent from superior colliculus (neural integrator) --> long-lead burst and omnipause neurons --> excitatory burst neurons --> motor neurons

Question 44

What is inhibitions role in saccade generation?

Answer 44

input from inhibitory burst neurons and connections made thru interneurons and tonic neurons

Question 45

What is the ratio for EOM innervation?

Answer 45

1:1

Question 46

What is a ventral stream?

Answer 46

Form related brain areas that runs along the sides of the head-- "what"

Question 47

What is a dorsal stream?

Answer 47

Motion related brain areas that run up top from back of head-- "where"

Question 48

T/F There is overlap between the ventral and dorsal stream

Answer 48

true

Question 49

What are the two excitatory burst nerve centers?

Answer 49

EBNH (brainstem for horizontal movements) and EBNV (reticular formation of the mesencephalon for vertical eye movements

Question 50

What do EBNs do?

Answer 50

jump-start; discharge in EBNs is 10-15 msec before the saccade itself-- injury can affect just horizontal or just vertical

Question 51

How does pursuit control work?

Answer 51

gets input back and forth from FEF aka impulse control