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Ocular Motility > Eye Movement Control Systems > Flashcards

Eye Movement Control Systems Flashcards

1
Q

Control System

A

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

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2
Q

Open loop system

A

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

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3
Q

T/F an open loop system only has one step

A

False, can be multistep

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4
Q

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

A

closed

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5
Q

Closed loop system

A

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

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6
Q

Idea of movement

A

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

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7
Q

What are the three components of the idea of movement?

A

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

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8
Q

Signal types

A

pulse, step, ramp

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9
Q

Pulse signal

A

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

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10
Q

Viscosity

A

Fat holding the eye still; overcome by pulse signal

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11
Q

Elasticity

A

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

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12
Q

Step signal

A

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

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13
Q

How are pulse and step signals depicted on a graph?

A

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

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14
Q

Ramp signal

A

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

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15
Q

Neural integrator

A

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

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16
Q

T/F there’s one kind of neural integrator

A

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

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17
Q

Example of neural integrator

A

Superior colliculus

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18
Q

Two types of neural integrators

A

Perfect and leaky

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19
Q

Perfect Neural Integrator

A

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

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20
Q

Leaky Neural Integrator

A

Signal decay= output decay

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21
Q

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

A

Proprioception from EOM tendons and/or efferent plan signals

22
Q

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

A

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

23
Q

Mesenchymal tissue

A

most prevalent early– infant development

24
Q

Myoblast cells

A

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

25
Q

How does myoblast differentiation take place?

A

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

26
Q

What age is the cut off for myoblasts?

A

8-9 years old

27
Q

Mature muscle fibers

A

Fibrillen and Felder

28
Q

Fibrillen fibers

A

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

29
Q

Felder fibers

A

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

30
Q

What happens with too few Felder fibers?

A

Convergence problem and inability to sustain at near

31
Q

Are muscle fibers continuous or broken?

A

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

32
Q

What is the effect of breaks in muscle fiber?

A

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

33
Q

What is the summary of Bruenech’s research?

A

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

34
Q

T/F There are stretch receptors in EOM tendons

A

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

35
Q

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

A

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

36
Q

Efferent copy of position signal

A

loops back to perceptual like kinesthetic neuron

37
Q

Saccadic neuron types

A

pause, burst, burst-tonic, tonic, motor

38
Q

Pause saccadic neuron

A

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

39
Q

Burst saccadic neuron

A

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

40
Q

Burst-tonic saccadic neuron

A

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

41
Q

Tonic saccadic neuron

A

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

42
Q

Motor saccadic neuron

A

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)

43
Q

Saccadic generation

A

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

44
Q

What is inhibitions role in saccade generation?

A

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

45
Q

What is the ratio for EOM innervation?

A

1:1

46
Q

What is a ventral stream?

A

Form related brain areas that runs along the sides of the head– “what”

47
Q

What is a dorsal stream?

A

Motion related brain areas that run up top from back of head– “where”

48
Q

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

A

true

49
Q

What are the two excitatory burst nerve centers?

A

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

50
Q

What do EBNs do?

A

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

51
Q

How does pursuit control work?

A

gets input back and forth from FEF aka impulse control

Ocular Motility (13 decks)

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