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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
Describe the central region of a muscle spindle?
* 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
You know that muscle spindles consist of 3-12 intrafusal fibers. What are the characteristics of these intrafusal fibers?
* innervated by small gamma motor neurons (group II afferents) * encapsulated within a sheath to form muscle spindle * run parallel to extrafusal fibers
27
True or False: Extrafusal fibers make up the "muscle fibers", which are innervated by alpha motor neurons.
True
28
What are the two types of intrafusal fibers?
* Nuclear bag fibers * Nuclear chain fibers
29
What do nuclear bag fibers, a type of intrafusal fiber, detect?
Detect rate of change in muscle length.
30
What do nuclear chain fibers, a type of intrafusal fiber, detect?
Detect static change in muscle length.
31
What are nuclear bag fibers innervated by?
* Group Ia afferents * Dynamic gamma efferents
32
What are nuclear chain fibers innervated by?
* Group II afferents * Static gamma efferents
33
How are nuclei arranged in nuclear bag fibers?
Multiple nuclei located in a central "bag-like" configuration.
34
How are nuclei arranged in nuclear chain fibers?
Multiple nuclei arranged in a single row.
35
Which type of intrafusal fiber is more nmerous in muscle spindles?
Muclear chain fibers are more numerous than nuclear bag fibers.
36
True or Fasle: The muscle spindle corrects for increase in msucle length (stretch).
True \*when muscle is stretched, spindle is stretched\*
37
In the sensory fibers from the central region of intrafusal fibers, what causes stimulation?
* lengthening of entire muscle * contraction of ends of intrafusal fibers
38
What does stimulation of sensory fibers from central region of intrafusal fibers result in?
Stimulation results in stimulation of alpha-motor neurons, resulting in contraction and shortening of muscle.
39
What are the types of sensory fibers of muscle spindles?
* Ia (primary fibers) * forms annulospiral ending * 17 micrometers in diameter * transmits at 70-120 m/sec * II (secondary fibers) * 8 micrometers
40
What fibers do muscle spindle gamma motor neurons innervate?
intrafusal fibers
41
What do muscle spindle gamma motor neurons do, besides innervate intrafusal fibers?
Adjust sensitivity of muscle spindle.
42
What other neuron is coactivated with muscle spindle gamma motor neurons?
* Coactivated with alpha-motor neurons. * stimulation results from: * lengthening of entire muscle
43
What simulation causes the coactivation of muscle spindle gamma motor neurons and alpha-motor neurons?
lengthening of entire muscle
44
What are the three types of gamma-motor neurons?
* A-gamma * gamma-dynamic * gamma-static
45
Which type of muscle spindle fibers do gamma-dynamic neurons excite?
Nuclear Bag Intrafual Fibers
46
Which type of muscle spindle fibers do gamma-static neurons excite?
Nuclear Chain Intrafusal Fibers
47
Which brain areas control gamma-motor neurons?
* Bulboreticular region of brain stem * Cerebellum * Basal nuclei * Cerebral cortex
48
What does the muscle spindle prevent?
Prevents jerkiness of body movements (damping).
49
For a dynamic stretch reflex, where are the signals transmitted from?
Signals transmitted from primary nerve endings.
50
For static reflex, where do muscle spindles get signals transmitted from?
Both primary and secondary endings.
51
What is the function of the dynamic stretch reflex?
Opposes sudden changes to muscle length.
52
What is the dynamic stretch reflex elicited by?
Rapid stretch or unstretch.
53
List the steps in the stretch reflex.
* 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
What is the Golgi tendon organ arranged in series with?
Arranged in series with extrafusal fibers.
55
How many muscle fibers attach to each Golgi organ?
10-15
56
What is the Golgi tendon organ?
* 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
What is the Golgi tendon organ stimulated by?
Contracting or stretching of muscle.
58
What does the Golgi tendon organ detect?
muscle tension
59
True or False: The Golgi tendon reflex is opposite of the stretch reflex.
True
60
What is the circuitry of the Golgi tendon organ?
Type Ib afferent (16 micrometer diameter) -( + )-\> inhibitory interneuron -( - )-\> anterior motor neuron
61

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

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