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Human Physiology 2 - Unit 2 - Zach H. > Lecture 10: Spinal Cord, Brainstem, & Cortex Control of Motor Function > Flashcards

Lecture 10: Spinal Cord, Brainstem, & Cortex Control of Motor Function Flashcards

1
Q

What are the 3 groups of neurons in the spinal cord?

A
  • Sensory (afferent)
  • Anterior motor neurons (efferent)
  • Interneurons
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2
Q

What is a motor unit composed of?

A
  • Composed of a single motor neurons and the muscle fibers it innervates.
  • Composed of extrafusal fibers.
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3
Q

What is a motor neuron pool?

A

Group of motor neurons that innervate fibers within the same muscle.

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4
Q

When talking about motor units, what does the term recruitment refer to?

A

Refers to the increase in tension of muscle contractions by the activation motor units (size principle).

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5
Q

What are the characteristics of small motor neurons?

A
  • innervate a few muscle fibers
  • lowest thresholds
  • fire first
  • generate smallest force
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6
Q

What are the characteristics of large motor neurons?

A
  • innervate many muscle fibers
  • highest thresholds
  • fire last
  • generate largest force
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7
Q

Do small or large motor neurons fire first?

A

Small motor units fire first.

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8
Q

What are Renshaw cells?

A

Inhibitory cells in anterior horns of the spainal cord.

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9
Q

From what cell type do Renshaw cells receive collateral branches from?

A

Receive collateral braches from alpha motor neurons.

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10
Q

What is the function of Renshaw cells?

A
  • Transmit inhibitory signals to surrounding motor neurons.
    • results in lateral inhibition
    • enhance fluidity of limb movement
  • Transmit inhibitory signals to same motor neuron.
    • results in recurrent inhibition
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11
Q

What action of Renshaw cells enhance fluidity of limb movement?

A

Transmission of inhibitory signals to surrounding motor neurons.

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12
Q

List the functions of interneurons?

A
  • 30x as numerous as anterior motor neurons
  • small and highly excitable
  • capable of spontaneous activity
  • responsible for most of spinal cord integrative function
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13
Q

Are interneurons capable of spontaneous activity?

A

Yes

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14
Q

Which cells are responsible for most of the spinal cord integrative functions?

A

Interneurons

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15
Q

Which fiber type does alpha motor neurons give rise to?

A

A-alpha fibers

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16
Q

List the different muscle sensors?

A
  • Muscle spindle (group Ia and II afferents)
  • Golgi tendon organ (group Ib afferents)
  • Pacinian corpuscles (group II afferents)
  • Free nerve endings (groups III and IV afferents)
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17
Q

Which muscle sensor detects noxious stimuli?

A

Free nerve endings (groups III and IV afferents)

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18
Q

Which muscle sensor detects vibration?

A

Pacinian corpuscles (group II afferents)

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19
Q

Which muscle sensor is arranged in parallel with extrafusal fibers?

A

Muscle spindle (group Ia and II afferents)

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20
Q

Which muscle sensor is arranged in series with extrafusal fibers?

A

Golgi tendon organ (group Ib afferents)

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21
Q

Which muscle fiber detects BOTH dynamic and static changes in muscle length?

A

Muscle spindle (groups Ia and II afferents)

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22
Q

Which muscle sensor detects muscle tension?

A

Golgi tendon organ (group Ib afferents)

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23
Q

Which nerve fiber types are myelinated and which are not?

A
  • Groups I, II, and III -> myelinated
  • Group IV -> non-myelinated
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24
Q

What type of neurons are muscle spindles innervated by?

A

small gamma motor neurons (group II afferents)

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25
Q

Describe the central region of a muscle spindle?

A
  • Central region of spindle has no contractile fibers; functions as a sensory receptor.
    • sensory fibers originate from central region
    • stretching of central region of intrafusal fiber stimulates sensory fibers
26
Q

You know that muscle spindles consist of 3-12 intrafusal fibers. What are the characteristics of these intrafusal fibers?

A
  • innervated by small gamma motor neurons (group II afferents)
  • encapsulated within a sheath to form muscle spindle
  • run parallel to extrafusal fibers
27
Q

True or False:

Extrafusal fibers make up the “muscle fibers”, which are innervated by alpha motor neurons.

28
Q

What are the two types of intrafusal fibers?

A
  • Nuclear bag fibers
  • Nuclear chain fibers
29
Q

What do nuclear bag fibers, a type of intrafusal fiber, detect?

A

Detect rate of change in muscle length.

30
Q

What do nuclear chain fibers, a type of intrafusal fiber, detect?

A

Detect static change in muscle length.

31
Q

What are nuclear bag fibers innervated by?

A
  • Group Ia afferents
  • Dynamic gamma efferents
32
Q

What are nuclear chain fibers innervated by?

A
  • Group II afferents
  • Static gamma efferents
33
Q

How are nuclei arranged in nuclear bag fibers?

A

Multiple nuclei located in a central “bag-like” configuration.

34
Q

How are nuclei arranged in nuclear chain fibers?

A

Multiple nuclei arranged in a single row.

35
Q

Which type of intrafusal fiber is more nmerous in muscle spindles?

A

Muclear chain fibers are more numerous than nuclear bag fibers.

36
Q

True or Fasle:

The muscle spindle corrects for increase in msucle length (stretch).

A

True

*when muscle is stretched, spindle is stretched*

37
Q

In the sensory fibers from the central region of intrafusal fibers, what causes stimulation?

A
  • lengthening of entire muscle
  • contraction of ends of intrafusal fibers
38
Q

What does stimulation of sensory fibers from central region of intrafusal fibers result in?

A

Stimulation results in stimulation of alpha-motor neurons, resulting in contraction and shortening of muscle.

39
Q

What are the types of sensory fibers of muscle spindles?

A
  • Ia (primary fibers)
    • forms annulospiral ending
    • 17 micrometers in diameter
    • transmits at 70-120 m/sec
  • II (secondary fibers)
    • 8 micrometers
40
Q

What fibers do muscle spindle gamma motor neurons innervate?

A

intrafusal fibers

41
Q

What do muscle spindle gamma motor neurons do, besides innervate intrafusal fibers?

A

Adjust sensitivity of muscle spindle.

42
Q

What other neuron is coactivated with muscle spindle gamma motor neurons?

A
  • Coactivated with alpha-motor neurons.
    • stimulation results from:
      • lengthening of entire muscle
43
Q

What simulation causes the coactivation of muscle spindle gamma motor neurons and alpha-motor neurons?

A

lengthening of entire muscle

44
Q

What are the three types of gamma-motor neurons?

A
  • A-gamma
  • gamma-dynamic
  • gamma-static
45
Q

Which type of muscle spindle fibers do gamma-dynamic neurons excite?

A

Nuclear Bag Intrafual Fibers

46
Q

Which type of muscle spindle fibers do gamma-static neurons excite?

A

Nuclear Chain Intrafusal Fibers

47
Q

Which brain areas control gamma-motor neurons?

A
  • Bulboreticular region of brain stem
  • Cerebellum
  • Basal nuclei
  • Cerebral cortex
48
Q

What does the muscle spindle prevent?

A

Prevents jerkiness of body movements (damping).

49
Q

For a dynamic stretch reflex, where are the signals transmitted from?

A

Signals transmitted from primary nerve endings.

50
Q

For static reflex, where do muscle spindles get signals transmitted from?

A

Both primary and secondary endings.

51
Q

What is the function of the dynamic stretch reflex?

A

Opposes sudden changes to muscle length.

52
Q

What is the dynamic stretch reflex elicited by?

A

Rapid stretch or unstretch.

53
Q

List the steps in the stretch reflex.

A
  • Stretching of muscle stretches group Ia afferent fibers.
  • Group Ia afferents synapse directly on alpha-motor neurons of same muscle.
  • The muscle contracts and decreases tension on muscle spindle.
  • Synergistic muscles are activated and antagonistic muscles are inhibited.
54
Q

What is the Golgi tendon organ arranged in series with?

A

Arranged in series with extrafusal fibers.

55
Q

How many muscle fibers attach to each Golgi organ?

56
Q

What is the Golgi tendon organ?

A
  • Encapsulated sensory receptor through which muscle tendon fibers pass.
    • stimulated by contracting or stretching of muscle
    • detects muscle tension
    • Golgi tendon reflex is opposite of the stretch reflex
57
Q

What is the Golgi tendon organ stimulated by?

A

Contracting or stretching of muscle.

58
Q

What does the Golgi tendon organ detect?

A

muscle tension

59
Q

True or False:

The Golgi tendon reflex is opposite of the stretch reflex.

60
Q

What is the circuitry of the Golgi tendon organ?

A

Type Ib afferent (16 micrometer diameter) -( + )-> inhibitory interneuron -( - )-> anterior motor neuron

Human Physiology 2 - Unit 2 - Zach H. (11 decks)

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