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MOVEMENT NEUROSCIENCE EXAM 2 > MODULE 8- Lower Motor Neurons Circuits + Motor Control > Flashcards

MODULE 8- Lower Motor Neurons Circuits + Motor Control Flashcards

1
Q

4 neural centers responsible for movement

A

-lower motor neurons
-upper motor neurons
-cerebellum
-basal ganglia

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2
Q

what are considered the “final common path” for initiating movement

A

lower motor neurons

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3
Q

basal ganglia

A

initiation of intended movement + suppression of unwanted movement

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4
Q

cerebellum

A

coordination of ongoing movement

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5
Q

motor cortex

A

planning, initiating, + directing voluntary movements

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6
Q

brainstem centers

A

stereotyped movements, postural control, + gain adjustments

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7
Q

local circuit neurons

A

sensorimotor integration + central pattern generation

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8
Q

motor neuron pools

A

all the motor neurons innervating a single muscle

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9
Q

lower motor neurons in the spinal cord + brainstem map what

A

the body’s musculature

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10
Q

each lower motor neuron innervates muscle fibers within a single/multiple muscles

A

a single muscle

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11
Q

somatotopic organization of motor neuron pools in ventral horn of spinal cord

A

-proximal muscles towards center of ventral horn
-distal muscles towards periphery of ventral horn

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12
Q

describe axons of medical ventral horn

A

extend several spinal cord segments + terminate bilaterally

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13
Q

axons of medial ventral horn are concerned with what

A

control of posture + locomotion

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14
Q

describe axons of lateral ventral horn

A

extend over fewer spinal cord segments + terminate only ipsilaterally

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15
Q

axons of lateral ventral horn are concerned with what

A

fine control of distal extremities

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16
Q

2 types of lower motor neurons found in the ventral horn

A

-alpha (α) motor neurons
-gamma (γ) motor neurons

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17
Q

alpha motor neurons

A

-innervate striated muscles
-make up part of the motor unit

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18
Q

gamma motor neurons

A

sensory receptors arranged in parallel with muscle spindles

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19
Q

the motor unit

A

-1 α-motor neuron +all the muscle fibers it innervates.
-1 α-motor neuron contacts a relatively wide area of muscle
-smallest unit of force that can be activated by the muscle

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20
Q

individual motor axons branch within muscles to do what

A

to contact fibers distributed over a wide area
-allows spread of activation for smoother force
-protects the muscle from becoming dysfunctional when 1 motor neuron dies out

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21
Q

where are motor neurons controlling muscles in the head, eyes + neck located

A

in the brainstem

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22
Q

innervation number

A

the number of muscle fibers innervated by 1 alpha motor neuron
-aka the number of fibers innervated by a motor unit

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23
Q

innervation differs across ____

A

muscle groups

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24
Q

gastroc force innervation number

A

1:2000

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25
Q

extraocular eye muscles innervation number

A

1:5

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26
Q

poliovirus

A

invades the motor neurons, leading to muscle weakness + impaired motor control due to fewer nerve signals reaching muscle fibers

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27
Q

polio- what happens to motor neurons that survive

A

develop new terminal axon sprouts that re-innervate orphaned muscle fibers

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28
Q

polio- total number of motor units increase/decrease

A

decrease

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29
Q

polio- muscle fibers that belong to a single motor unit increase/decrease

A

increase

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30
Q

what does polio result in

A

enlarged, less efficient motor units, which are easier to fatigue, further affecting fine motor control

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31
Q

how do alpha motor neurons vary

A

in size

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32
Q

alpha motor neuron size is proportional to what

A

the amount of muscle force that can be generated

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33
Q

slow (S) motor units

A

sustained muscular contraction
-such as for maintaining posture

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34
Q

fast fatigable (FF) motor units

A

generating large forces for short periods of time
-such as for jumping
-few mitochondria

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35
Q

fast fatigue resistant (FR) motor units

A

generate 2X force as slow ones
-resistant to fatigue

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36
Q

what motor units have few mitochondria

A

fast fatigable (FF) motor units

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37
Q

twitch contraction

A

muscle tension in response to a single AP

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38
Q

see slides 13-15

A
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39
Q

motor neuron innervation to striated muscle changes in response to ____

A

exercise

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40
Q

chronic electrical nerve stimulation transforms the metabolic + contractile properties of muscle from FF to ____ type

A

S type

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41
Q

size principle

A

the orderly systematic recruitment of motor neurons from S to FR to FF muscle fibers as the physical demands of the task increases

42
Q

motor units are recruited from ____ to ____

A

weakest to strongest

43
Q

as the rate of stimulation on muscle tension increases…

A

AP firing frequency increases ->
temporal summation ->
unfused tetanus ->
fused tetanus

44
Q

increase in force occurs with increased ____

A

firing rate

45
Q

as the amount of voluntary force increases, what increases

A

the number + firing rate of active motor units

46
Q

the lowest firing rates of motor units during a voluntary movement are on the order of ____/second

A

8/second

47
Q

firing rate rises to about ____ per second

A

20-25 per second

48
Q

normal firing rates are much less than those required for ____

A

fused tetanus

49
Q

local circuitry mediates reflexes that rapidly adjust muscle tension in response to sensory input

slide 23?

A

8-10 intrafusal fibers arranged in parallel
-dynamic nuclear bag fibers
-static nuclear bag fibers
-nuclear chain fibers

50
Q

_____ coil around fibers

A

large-diameter afferents

51
Q

Ia afferent innervates what

A

all 3 types of fibers

52
Q

what does Ia afferent signal

A

velocity

53
Q

II afferent innervates what

A

nuclear chain fibers

54
Q

what do II afferent signal

A

length

55
Q

activation of ____ pulls central region of intrafusal fiber

A

gamma motor neuron

56
Q

activiation of gamma motor neuron contracts intrafusal fibers, making which afferents more sensitive

A

Ia

57
Q

stretching muscle leads to what

A

increased discharge (APs) from Ia afferents

58
Q

alpha motor neurons of agonist/antagonist increase discharge (APs) causing extrafusal muscle fibers to contract

A

agonist

-monosynaptic

59
Q

reciprocal innervation

A

-excite agonist muscle that is stretched
-inhibits antagonist muscle
-monosynaptic

60
Q

disynaptic pathway is mediated by what

A

reciprocal Ia inhibitory interneurons

61
Q

what happens during extrafusal contraction

A

the spindle afferents are quiet

62
Q

during extrafusal contraction, why are spindle afferents quiet

A

because the muscle spindle is not stretched – it is not loaded

63
Q

during alpha + gamma coactivation, what happens

A

when extra + intrafusal fibers contract, there is no change in spindle afferent firing, as they are being stretched or loaded

64
Q

stretch reflex operates as a feedback loop to regulate what

A

muscle length

65
Q

gain of stretch reflex depends on the level of what

A

gamma motor neuron activity

66
Q

high gain of stretch reflex

A

small stretch ->
large increase in alpha motor neuron activation

67
Q

low gain of stretch reflex

A

larger stretch is required to produce same amount of tension in extrafusal fibers

68
Q

gain of stretch reflex is high during what tasks

A

difficult tasks or uncertain conditions
-ex: walking across a narrow beam or standing on a moving bus

69
Q

golgi tendon organ

A

encapsulated nerve endings at junction of tendon + muscle

70
Q

what axons innervate GTOs

A

Ib axons

71
Q

how are GTOs arranged with extrafusal fibers

A

in series

72
Q

GTOs sense changes in ____ of the muscle

A

tension

73
Q

GTOs are sensitive/insensitive to passive stretch

A

insensitive

74
Q

GTOs work by positive/negative feedback system

A

negative

75
Q

decreased/increased GTO leads to APs of the Ib neuron

A

increasd

76
Q

which horn do GTOs enter

A

dorsal horn

77
Q

GTOs excite/inhibit alpha motor neuron of agonist muscle

A

inhibit

78
Q

GTOs excite/inhibit alpha motor neuron of antagonist muscle

A

excite

79
Q

GTOs prevent what

A

excessive tension

80
Q

GTOs maintain what during muscle fatigue

A

steady tone

81
Q

2 functions of GTOs

A

-prevent excessive tension
-maintain steady tone during muscle fatigue

82
Q

under passive stretch or tension, what happens to muscle spindle activity

A

increases + is maintained

83
Q

under passive stretch or tension, what happens to GTO activity

A

relatively unaffected

84
Q

when load is increased…

A

the increased force is transmitted to the GTO ->
increase in firing rate of its Ib afferents

85
Q

flexion reflex

A

-cutaneous (nociceptor) stimulated
-excites interneuron circuits in the spinal cord

86
Q

flexion reflex causes inhibition of flexor/extensor of stimulated foot

A

extensor

87
Q

flexion reflex causes excitation of flexor/extensor of stimulated foot

A

flexor

88
Q

flexion reflex is ___ in the other limb

A

opposite
-crossed extension reflex

89
Q

what does flexion reflex lead to

A

withdrawal of the limb from painful stimuli

90
Q

central pattern generator

A

local circuits in the spinal cord for generating rhythmic stereotypical patterns of movement, such as in walking, running, etc.

91
Q

central pattern generator extra info

A

-alternating between stance phase and swing phase
-flexors + extensors activated reciprocally
-increased speed means less time between each cycle
-module receives input from excitatory rhythm-generating interneurons, which are reciprocally inhibited by interneurons

92
Q

what alternates during stepping

A

contractions of flexor + extensor muscles

93
Q

after recovering from surgery (transection of spinal cord), are the cats hindlimbs able to walk on treadmill

A

yes
-reciprocal bursts of electrical activity can be recorded from flexors during the swing phase and from extensors during the stance phase of walking

94
Q

the basic rhythmicity of stepping is produced by what

A

neuronal circuits contained entirely within the spinal cord
-separate CPG for each leg

95
Q

are supraspinal commands necessary for producing the basic motor pattern for stepping

A

NO

96
Q

what initiates + modulates CPG activity

A

mesencephalic locomotor region

97
Q

do CPG networks require sensory input

A

NO

98
Q

what are CPG networks strongly regulated by

A

input from limb proprioceptors (e.g., speed changes)

99
Q

lower motor neuron syndrome

A

caused by damage to lower motor neurons

-depending on the extent of damage, can lead to paralysis, weakness, or loss of tone
-muscles may exhibit fasciculations and fibrillations – spontaneous twitches characteristic of degenerating motor units + fibers, respectively

100
Q

how is lower motor neuron syndrome clinically diagnosed

A

EMG

101
Q

amyotrophic lateral sclerosis (ALS)/Lou Gehrig’s disease

A

degeneration of lower motor neurons +/or upper motor neurons

MOVEMENT NEUROSCIENCE EXAM 2 (15 decks)

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