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Neuro M101A > Module 2: Lower Motor Neurons > Flashcards

Module 2: Lower Motor Neurons Flashcards

1
Q

what does ‘motor systems’ mean

A

behavior and the biology that creates it; the neural connections that hook up to our brain with our muscles that allow us to move

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2
Q

where do simple behaviors usually have circuits in

A

brainstem and spinal cord

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3
Q

where do complex behaviors usually have circuits in

A

higher levels of the brain

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4
Q

descending systems composition

A

motor cortex, brainstem centers

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5
Q

motor cortex function

A

planning, initiating, and directing voluntary movements

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6
Q

brainstem centers function

A

basic movements and postural control

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7
Q

basal ganglia connectivity

A

to the motor cortex

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8
Q

basal ganglia function

A

gating proper initiation of movement

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9
Q

cerebellum connectivity

A

brainstem centers

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10
Q

cerebellum function

A

sensory motor coordination of ongoing movement

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11
Q

spinal cord and brainstem circuits composition

A

lower circuit neurons and motor neuron pools

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12
Q

where do motor neuron pools project to

A

skeletal muscles

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13
Q

where do local circuit neurons project to

A

motor neuron pools

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14
Q

where do sensory inputs first project to

A

local circuit neurons

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15
Q

where do descending systems mainly project to

A

local circuit neurons

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16
Q

where do descending systems mildly project to

A

motor neuron poolss

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17
Q

general classes of movement

A
  1. reflexes
  2. rhythmic
  3. voluntary
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18
Q

where does the circuit for reflexes lie

A

simple neural circuit that resides in spinal cord or brainstem

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19
Q

main component of rhythmic movement

A

central component (central pattern generator) that regulates brainstem or spinal cord oscillatory circuit

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20
Q

what parts of the brain does voluntary movement require

A

‘higher’ brain levels such as cortex, basal ganglia, cerebellum

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21
Q

In general, a reflex uses neurons located in _____ which voluntary movement requires neurons located in _______

A

the spinal cord; the cortex

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22
Q

what is the relationship between sensation and movement

A

there is blurring; you can’t separate sensory from motor systems
- behavior is continuously motivated and guided by sensory input

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23
Q

feed-forward control

A

watching a ball fall and moving the arm into a position to catch it

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24
Q

feedback control

A

after the ball hits the hand, the movement of the arm to return to its original position

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25
Q

kinds of tracer injections

A

anterograde, retrograde

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26
Q

anterograde dye path

A

travels from cell body –> axons
- yields complete reconstruction of axons

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27
Q

retrograde dye path

A

travels from nerve terminals back toward soma

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28
Q

pseudorabies function

A

jump synapses giving you multiple steps in the circuit
- often toxic

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29
Q

in vitro physiology

A

‘in a dish’
- dye is injected into two cells that appear to be synaptically coupled to determine connectivity

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30
Q

in vivo calcium imaging

A
  • inject a virus encoding a protein that fluoresces in response to ca
  • miniscope lets you record ca signals as a proxy for neural activity
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31
Q

optogenetics

A

neurons are triggered to become light sensitive and fire when activated by light

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32
Q

techniques to record patterns of energy use by the brain during behavior

A
  • positron emission tomography (PET)
  • functional or structural magnetic resonance imaging (MRI)
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33
Q

techniques to record patterns of immediate early gene activation

A

immediate early gene (IEG) mRNA detection

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34
Q

what is IEG

A

a gene whose mRNA is rapidly transcribed following neuronal activity within the active neuron
- requires a gene probe to detect them

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35
Q

what can IEG reveal

A

neurons that were active prior to death
- poor man’s fMRI

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36
Q

which of the following techniques would be most useful for discovering whether two neurons are synaptically connected to one another?

A

d. in vitro electrophysiology

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37
Q

types of muscle

A

smooth vs striated

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38
Q

types of striated muscle

A

cardiac vs skeletal

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39
Q

what is skeletal muscle composed of

A

extrafusal and intrafusal muscle fibers

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40
Q

extrafusal muscle fiber function

A

generate the mechanical forces required for movement

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41
Q

intrafusal muscle fiber function

A

embedded in the extrafusal fibers; sensory ending wrap around and report how much tension is in the muscle

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42
Q

what are the extrafusal fibers innervated by

A

alpha motor neurons

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43
Q

where do the cell bodies of alpha motor neurons lie

A

ventral horn of the spinal cord

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44
Q

what are the intrafusal fibers innervated by

A

gamma motor neurons

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45
Q

where do gamma motor neuron cell bodies lie

A

adjacent to alphas

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46
Q

synergist

A

muscle that produces a similar motor action when contracted
- eg soleus and gastrocnemius muscles

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47
Q

antagonist

A

muscle that produces the opposite motor action
- eg flexors vs extensor, biceps vs triceps

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48
Q

contralateral

A

muscle of the opposite limb

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49
Q

how can alpha motor neurons be labeled

A

by injecting a retrograde dye into the muscle

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50
Q

what kind of neurons. do lower motor neuron circuits include

A

alpha neurons and local interneurons

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51
Q

how are alpha motor neurons organized relative to the muscles that they control

A

somatotopically

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52
Q

topography in neuroscience

A

mapping of an external surface or stimulus onto a biological substrate

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53
Q

which direction does the somatotopic map run?

A
  • medial to lateral; motor neurons for distal muscles are located laterally a d proximal muscles are located more medially
  • segmentally; motor neurons are located at the same segmental level as the muscles they innervate
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54
Q

local circuit neurons

A

cell bodies and axons are all located within the spinal cord

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55
Q

projection neuron

A

cell body and nerve terminal are in separate brain areas

56
Q

interneuron placement

A

cell body and terminal are within the same general brain area

57
Q

motor unit

A

single alpha motor neuron and all the muscle fibers it innervates

58
Q

what do alpha motor neurons release at neuromuscular junction

A

acetylcholine

59
Q

what does acetylcholine release cause

A

an ‘endplate’ potential (epp), ie an epsp in the muscle fiber
- if large enough, there is an action potential –> the muscle twitches

60
Q

three ways to increase muscle force

A
  • stimulate a given motor unit more frequently
  • recruit more motor units
  • recruit fast-fatiguable motor units in addition to slow ones
61
Q

example of slow fatiguable muscles

A

soleus

62
Q

where is the threshold for slow fatiguable muscles

A

low

63
Q

comparative force produced by slow fatiguable

A

weaker

64
Q

slow fatiguable soma size

A

small

65
Q

slow fatiguable capillary bed color

A

red

66
Q

slow fatiguable energy source

A

oxidative
- requires blood flow

67
Q

slow fatiguable ration neuron/fiber

A

1:180

68
Q

slow fatiguable contraction speed

A

slow

69
Q

thanksgiving example for slow fatiguable muscles

A

dark meat

70
Q

fast fatiguable muscle example

A

gastrocnemius

71
Q

fast fatiguable muscle threshold

A

high

72
Q

fast fatiguable muscle force

A

stronger

73
Q

fast fatiguable muscle soma size

A

large

74
Q

fast fatiguable muscle capillary bed color

A

pale

75
Q

fast fatiguable energy source

A

glycolytic
- uses enzymes that run out

76
Q

fast fatiguable ratio neuron/fiber

A

1:2000

77
Q

fast fatiguable contraction speed

A

fast

78
Q

fast fatiguable thanksgiving example

A

white meat

79
Q

recruitment order of motor neurons

A

slow fatiguable –> fast fatigue resistant –> fast fatiguable

80
Q

what is in charge of the muscle fiber type?

A

alpha motor neuron

81
Q

what muscle type is a soleus muscle with a slow alpha motor neuron connection

A

slow

82
Q

what muscle type is a gastrocnemius muscle with a fast alpha motor neuron connection

A

fast

83
Q

what muscle type is a soleus muscle with a fast alpha motor neuron connectino

A

fast-like

84
Q

what muscle type is a gastrochemius muscle with a slow alpha motor neuron connection

A

slow-like

85
Q

what does 10 Hz stimulation favor

A

the development of slow units

86
Q

what does 100 Hz stimulation favor

A

the development of fast units

87
Q

what is meant by a circuit

A

a series of neurons synaptically linked that work together to perform some function
- usually have an ‘input’ and an ‘output’

88
Q

afferents

A

nerves that carry info into the CNS

89
Q

efferents

A

nerves that send signals out of the CNS

90
Q

where are most motor neurons located

A

in the ventral horn

91
Q

1a afferents

A

sensory neurons

92
Q

where are 1a afferents cell bodies located

A

dorsal root ganglia

93
Q

proprioceptors

A

provide info about self-movement, force, & body position
- spindles & their afferents are examples

94
Q

what neurons are essential for the myotatic reflex

A

1a afferents

95
Q

when are mechanosensitive ion channels on the 1a afferents gated

A

when the intrafusal fibers are stretched

96
Q

what happens when intrafusal fibers on 1a afferents are stretched

A

stretch –> opens channels –> sodium flows in –> action potential travels into the spinal cord

97
Q

metaphor for myotatic reflex

A

like putting your fingers into a fishing net and someone stretching it

98
Q

how does the knee tap reflex occur

A

tap on patellar tendon stretches quadriceps –> activates the muscle spindle –> burst of APs in 1a spindle afferents –> release of glutamate onto the alpha motor neuron innervating the extensor –> motor neuron depolarizes –> fires APs –> releases ACh onto the muscle –> muscle contracts

99
Q

what does the burst of action potentials in the 1a spindle afferents cause in the knee tap reflex

A

a release of glutamate onto the alpha motor neuron innervating the extensor

100
Q

what does a release of glutamate on the alpha motor neuron innervating the extensor cause in the knee tap reflex

A

the motor neuron depolarizes and fires action potentials

101
Q

what happens when the motor neuron depolarizes and fires an action potential in the knee tap reflex

A

it releases ACh onto the muscle and it contract

102
Q

what is the function of the interneuron in terms of spindle afferents

A

the spindle afferents also synapse on an inhibitory interneuron which releases GABA onto the alpha motor neuron innervating the flexor; motor neuron hyperpolarizes and the muscle relaxes

103
Q

What does stimulation of nocireceptive sensory fibers do

A

excite the ipsilateral flexor and inhibit the extensor
- on the contralateral side, stimulus inhibits the flexor and stimulates the extensor

104
Q

what happens when gamma motor neurons fire?

A

intrafusal fibers contract

105
Q

what do small gamma motor neurons do

A

adjust the tension, or ‘gain’ in the spindle

106
Q

what does increasing the tension of muscle fibers do

A

increases the sensitivity of the system

107
Q

what are Golgi tendon organs

A

second sensory system associated with muscles

108
Q

what is the difference between Golgi tendon organs and muscle spindles

A

tendons are in series with the muscle while spindles are in parallel

109
Q

what evokes the biggest response in the Golgi tendon system

A

contraction

110
Q

happens when a tendon is stretched

A

mechanosensitive ion channels on the 1b afferents gate
- happens when the muscle contracts

111
Q

characteristics of muscle spindles (signal, position, and senstivity)

A
  • signals mostly about muscle length
  • it is in parallel with extrafusals
  • sensitivity is set by gamma motor neurons in spinal cord
112
Q

characteristics about Golgi tendon organ (signals, position, and sensitivity)

A
  • signals mostly about muscle contraction
  • is in series with extrafusals
  • no known setting of sensitivity
113
Q

does rhythmic walking require sensory info?

A

no

114
Q

first step of rhythmic activity in a spinal interneuron

A

without glutamate the receptors are closed and there is no activity

115
Q

what happens when glutamate is applied in rhythmmic activity in a spinal interneuron

A

it binds to both the AMPA and NMDA receptors

116
Q

what happens when glutamate binds to the AMPA and NMDA receptors in rhythmic activity in a spinal interneuron

A

the membrane begins to depolarize due to sodium ions entering through the AMPA receptor

117
Q

what initially happens to the NMDA receptor in rhythmic activity in a spinal interneuron

A

initially no ions flow through the NMDA receptor because the channel is blocked by magnesium

118
Q

what happens as the membrane starts to depolarize in rhythmic activity in a spinal interneuron

A

the magnesium is electrostatically repulsed

119
Q

what happens when the AMPA and NMDA receptors open in rhythmic activity in a spinal interneuron

A

they let in sodium leading to lots of action potentials
- NMDA receptor is also permeable to calcium

120
Q

what happens over time in rhythmic activity in a spinal interneuron

A

the AMPA receptor desensitizes and closes, then resensitizes and re-opens because glutamate is still around

121
Q

what happens when calcium that comes in through the NMDA receptor binds to the calcium-activated potassium channel

A

the receptor opens and lets potassium out of the cell, which repolarizes the membrane

122
Q

what happens during the hyperpolarization in rhythmic activity in a spinal interneuron

A

magnesium re-blocks the NMDA receptor but once the AMPA receptors resensitize, the cycle repeats

123
Q

true or false: in vitro application of glutamate ensures that those neurons expressing glutamate receptors will be tonically (consistently) active

A

false

124
Q

what is one way to translate tonic excitation into alternating rhythmic

A

reciprocol inhibition

125
Q

first step of reciprocal inhibition

A

action potentials causing glutamate release onto both excitatory interneurons

126
Q

what happens after glutamate is released onto both excitatory interneurons in reciprocal inhibition

A

stochastically, the extensor excitatory interneuron fires first

127
Q

what happens after the extensor excitatory interneuron fires first in reciprocal inhibition

A

both excitatory interneurons have axon collaterals that release glutamate onto inhibitory interneurons

128
Q

what happens after both excitatory interneurons release glutamate onto inhibitory internuerons in reciprocal inhibition

A

one of the inhibitory interneurons releases GABA onto the top excitatory interneuron, hyperpolarizing it so it doesn’t fire

129
Q

what happens after an excitatory interneuron is hyperpolarized in reciprocal inhibition

A

an inhibitory interneuron also releases GABA onto itself via an autapse
- so it no longer inhibits the flexor interneuron

130
Q

what happens after the first interneuron autapse?

A

the flexor interneuron is free to respond to the glutamate and begins firing
- also releases glutamate onto the other inhibitory interneuron

131
Q

what happens after the flexor interneuron responds to the glutamate

A

the inhibitory interneuron releases GABA onto the extensor excitatory interneuron, hyperpolarizing it so it no longer fires

132
Q

what happens after the excitatory interneuron is hyperpolarized in reciprocal inhibition DELETEEEE

A

an inhibitory interneuron also releases GABA onto itself via an autapse
- it inhibits itself and stops inhibiting the extensor excitatory interneuron

133
Q

what happens after an inhibitory interneuron inhibits itself and stops inhibiting the extensor motor neuron

A

the extensor excitatory interneuron is now able to respond to the glutamate and starts firing, thereby regenerating the cycle

134
Q

what mechanisms can lead to escape from inhibition

A

inhibitory autapse, fatigue of presynaptic release, or accommodation of the postsynaptic response

135
Q
A

Neuro M101A (6 decks)

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