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Clinical Neuroscience > Lower Motor Neurons > Flashcards

Lower Motor Neurons Flashcards

1
Q

What disease is this?

Degnerative disease of both upper and lower motor neurons in the nervous system?

A

Amyotrophich Lateral Sclerosis

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2
Q

Which motor activity system is this? (lower or upper)

Sum of the supraspinal descending influences on the lower motor neuron

A

Upper Motor Neuron System

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3
Q

What part of the brain do descending motor tracts arise from?

A

Cortex and brainstem

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4
Q

What motor tracts are from the cortex?

A
  • Corticospinal
  • Corticobular
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5
Q

What motor tracts are from the brainstem?

A
  • Vestibulospinal
  • Reticulospinal
  • Rubrospinal
  • Tectospinal
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6
Q

How is voluntary movement controlled?

A

Top-down; from the brain to spinal cord to muscle

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7
Q

Where does the descending motor system start with a decision when starting an action?

A

In the anterior region of the frontal lobe or the motor cortex to activate upper motor neurons

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8
Q

What makes up the descending control center?

A

Upper motor neurons in the motor cortex and brainstem

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9
Q

What actions is the motor cortex involved in?

A

Planning, initiating, and directing voluntary movements

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10
Q

What actions are the brainstem centers invovled in?

A

Rhythmic, sterotyped movements and postural control

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11
Q

What happens after a decision is made in the anterior region of the frontal lobe?

A

Motor planning areas and control circuits are activated

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12
Q

Where are the control circuits found?

A

Cerebellum and basal ganglia

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13
Q

What does the control center do?

A

Regulate activity of descending upper motor neurons in the motor cortex and brainstem centers

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14
Q

What action is the basal ganglia invovled in?

A

Initiation of intended movement and suppression of unwanted movement

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15
Q

What action is the cerebellum involved in?

A

Coordinates ongoing movement

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16
Q

What happens after motor areas and control circuits are activated?

A

Upper motor neurons deliver singals to local spinal and brainstem circuits and motor neuron pools (lower motor neurons)

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17
Q

What processs occur in the local circuit neurons?

A

Sensorimotor integration and central pattern generation processes

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18
Q

Where do the local circuit neuron proccesses occur?

A

Brainstem and spinal interneurons

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19
Q

What is the final event in activation of voluntary movement?

A

Transmission of signals from the lower motor neurons directly to skeletal muscles, eliciting contraction of muscle fibers

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20
Q

What is the following a definiton of?

Composite of voluntary and involuntary motor activity

A

Movement

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21
Q

Where are voluntary movements directed?

A

Distal muscle groups

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22
Q

How is lower motor neuron innervation mediated?

A

Through the lateral corticospinal tract

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23
Q

What muscle groups does involuntary movement involve?

A

Proximal and truncal muscle groups

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24
Q

Why is involuntary movement critical?

A

Critical for postural stability

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25
Q

What tract are postural adjustments under?

A

Anterior Corticospinal tract

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26
Q

What are the tracts that mediate postural stability?

A
  • Vestibulospinal
  • Reticulospinal
  • Rubrospinal
  • Tectospinal
27
Q

What tract does the brainstem pathway recieve input from?

A

Corticospinal pathways

28
Q

Lower motor neurons are the only neurons that convey signals to ____ and ____ skeletal muscle fibers

A

extrafusal; intrafusal

29
Q

What neurons are the final common pathways for signal transduction

A

Lower motor neurons

30
Q

Where are LMN located?

A

Anterior horn of the spinal cord and motor nuclei of cranial nerves in the brainstem

31
Q

LMN are organized into circuits to do what?

A

Sort and regulate the multitude of descending influences so that activity of truncal, proximal, and distal muscle groups are coordinated

32
Q

Where are cell bodies of the spinal lower motor neurons located?

A

Ventral horn

33
Q

Where do the cell bodies of the spinal LMN leave the spinal cord?

A

Ventral root

34
Q

Cell bodies whose axons project to a single muscle are clustered in ____ ____

A

Motor pools

35
Q

Medially located pools of motor cells bodies innervate what muscles?

A

Axial and proximal muscles

36
Q

Anteriorly located pools innervate what muscle?

A

Extensor muscles

37
Q

Posterior pools within ventral horn innervate what?

A

Flexor muscles

38
Q

Where are the cell bodies of alpha and gamma motor neurons located?

A

Ventral horn of the spinal cord

39
Q

Alpha and gamma motor neuron axons leave the spinal cord via ____ ____ then travel through the ____ ____ and then travel through the ____ ____ to reach skeletal muscle

A

ventral rool; spinal nerve; peripheral nerve

40
Q

Is the following alpha or gamma motor neuron?

large cell bodies and large myelinated axons

A

Alpha

41
Q

Is the following alpha or gamma motor neuron?

Medium sized myelinated axons

A

Gamma

42
Q

Where do the axons are alpha motor neurons project to?

A

Extrafusal skeletal muscles
branching into numerous terminals

43
Q

Where do gamma motor neurons project to?

A

Intrafusal fibers in the muscle spindle

44
Q

What does a motor unit consist of?

A

Alpha motor neuron and the muscle fibers it innervates

45
Q

What is the following a definition of?

Activated pattern that maintains the stretch on the central region of the muscle spindle intrafusal fiberes by contracting the ends of the intrafusal fibers when the extrafusal fibers actively contract

A

Alpha-gamma coactivation

46
Q

What is the purpose of the alpha-gamma coactivation?

A

Maintain stretch sensivity of the muscle spindle when extrafusal muscle fibers contract

47
Q

Why does alpha-gamma coactivation occur?

A

Because most sources of input to alpha MN have collaterals to gamma MN

MN = motor neurons

48
Q
A
49
Q

What neurotransmitter is released when alpha MN is activated?

A

ACh

50
Q

Smaller diameter slower conducting alpha MN innervates what type of motor unit?

A

Slow twitch

51
Q

Large diameter and faster conducting alpha MN innervated what type of motor unit?

A

Fast twitch

52
Q

What is the following a defintion of?

Order of recruitment from smaller to larger alpha motor neurons

A

Henneman’s size principle

53
Q

What does resistance to stretch that muscles generated depend on?

A

Muscle length

54
Q

A stretched muscle generates ____ resistance to stretch than when its ____

A

more; shortened

55
Q

What factors determine the total resistance to muscle stretch?

A
  • Active contraction
  • titin
  • connective tissue
  • weak actin-myosin bonds
56
Q

What is the following a defintion of?

Resistance to stretch in a resting muscle

A

Muscle tone

57
Q

When muscle tone is normal, resistance to passive stretch is what?

A

Minimal

58
Q

What is normal resistance to slow passive stretch in relaxed muscle produced by?

A

Weak actin-myosin bonds and titin

59
Q

The following functions are of what chemical?

Maintains the position of myosin relative to actin and prevents sacromere from being pulled apart

A

Titin

60
Q

How are weak actin-myosin bonds formed?

A

Myosin attaches to actin but myosin head doesn’t swivel so there is no power stroke

61
Q

What are the two forces that act on a joint to determine its resistance to movement called?

A

Elastic and contractile forces

62
Q

What does upper limb contraction allow for?

A

Precise movements

63
Q

What does lower limb contractions allow for?

A

Enables person to stand on unstable surface

Clinical Neuroscience (22 decks)

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