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D1 Spring - Physiology Exam 2 > 2/23: Skeletal Muscle and Reflexes II > Flashcards

2/23: Skeletal Muscle and Reflexes II Flashcards

1
Q

What are the three types of muscle fibers?

A

Slow twitch: Type I
Fast twitch:
Oxidative-glycolytic: Type IIA
Glycolytic: Type IIB

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2
Q

Rank the muscle fibers in order of diameter?

A

Type I - small
Type IIA - moderate
Type IIB - large

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3
Q

Rank the muscle fibers regarding resistance to fatigue

A

Type I - slow
Type IIA - fast resistant
Type IIB - Fast fatigable

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4
Q

How can a skeletal muscle fibers size change in response to use?

A
  1. Hypertrophy
  2. Atrophy
  3. Sarcopenia
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5
Q

When does jaw muscle thickness decrease?

A

With age

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6
Q

How do skeletal muscles change in fiber types as they are used?

A

With age, type 1 fibers decrease, type 2 fibers increase

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7
Q

How is contraction determined?

A

The amount of load and the force the muscle generates determines the type of contraction

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8
Q

What are two types of contraction?

A
  1. Isometric contraction
  2. Isotonic contraction
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9
Q

What is isometric contraction?

A

Force produced is less than the load; no movement
ex: Plank, not being able to curl 700lbs

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10
Q

What is isotonic contraction?

A

Force produced is great enough to move a load
ex: being able to curl 5 lbs

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11
Q

When does the force of contraction increase until?

A

The isometric contraction becomes an isotonic contraction - not always possible

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12
Q

Describe what happens with the sarcomere and muscle length in isometric contractions

A
  • sarcomeres shorten
  • muscle length remains the same
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13
Q

Describe what happens with the sarcomere and muscle length in isotonic contractions

A
  • sarcomeres shorten
  • muscles shorten
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14
Q

____ crossbridges = _____ force

A

More; more

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15
Q

What are two ways to increase the total force of a contraction?

A
  1. Increasing the number of muscle fibers contracting
  2. Increasing the frequency of fiber activation
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16
Q

What is a motor unit?

A

The alpha motor neuron and the muscle fibers it innervates

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17
Q

How are motor units recruited?

A

In order of size
a. small motor units first

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18
Q

Smallest motor units control _______ fibers

A

Fewer

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19
Q

What happens with an increase in the number of motor units?

A

There is an increase in tension produced by contraction of a muscle = spacial summation

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20
Q

What are small motor units composed of?

A

Slow twitch oxidative fibers

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21
Q

What has the slowest threshold for firing and are recruited first?

A

Slow twitch fibers

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22
Q

What are large motor units composed of?

A

Fast-twitch glycolytic fibers

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23
Q

What has the highest threshold and are recruited last?

A

Fast twitch fibers

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24
Q

How can you increase the total force of a contraction?

A
  1. Increasing the number of muscle fibers contracting (motor unit recruitment)
  2. Increasing the frequency of fiber activation
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25
Q

What happens if you increase the frequency of motor nueorn stimulation?

A

Increase the amount of tension produced
- the tension produced in response to each action potential will sum if the muscle has not yet relaxed

26
Q

For a single muscle twitch (one muscle fiber), how is the tension developed altered?

A

By sarcomere length

27
Q

What is optimal length?

A

Where there is the best degree of overlap between the thick and thin filaments

28
Q

What can form at optimal length?

A

The greatest number of actin/myosin cross bridges, which results to maximal tension production

29
Q

What happens if the muscle is not stretched enough or if its stretched too much?

A

Tension is reduced

30
Q

What does velocity of contraction (distance moved/time) dependent on?

A

the load a fiber is contracting against

31
Q

The greater the load, the _________ the speed of contraction

A

SLOWER
- as load increases, velocity, decreases

32
Q

Besdies load, what else dictates the speed of contraction?

A

Fiber type
Type I: isoform, slower ATPase activity
Type II: Fasy myosin ATpase

33
Q

What are the types of skeletal muscle reflexes?

A

A. Stretch reflex (muscle receptors)
B. Golgi tendon reflex (tendon receptors)

34
Q

What do gamma motor neurons innervate?

A

The ends of the intrafusal muscle in the spindle

35
Q

What are sensory fibers?

A

1a fiber (muscle spindle)
1b fiber (golgi tendon)

36
Q

What are extrafusal fibers?

A

Skeletal muscle fibers/cells that produce the contraction

37
Q

What kind of motor neuron is in extrafusal fibers?

A

Alpha motor neuron

38
Q

What is the alpha motor neuron?

A

Efferent neuron that releases ACh and causes contraction of the extrafusal fiber (skeletal muscle)

39
Q

What is the muscle spindle?

A

Small structure within the extrafusal fibers that contains intrafusal fibers that have sensory endings wrapped around them that are sensitive to changes in muscle length

40
Q

What kind of motor neuron does the muscle spindle have?

A

Gamma motor neuron

41
Q

What is the gamma motor neuron?

A

Efferent neuron that causes contraction of intrafusal fibers so they mimic what the EF fibers are doing

42
Q

How many muscle spindles do jaw closers have?

A

Lots of muscle spindles

43
Q

How many muscle spindles do jaw openers have?

A

Few to none

44
Q

What are the steps that occur when the muscle stretches in the muscle spindle reflex?

A
  1. Muscle stretches, the sensory fibers (1a) of the muscle spindle are squeezed
  2. Afferent information enters the spinal cord and
    a. Activates the alpha motor neuron
    b. activates the gamma motor neuron
45
Q

What happens when the alpha motor neuron is activated?

A

i. This stimulates muscle (extrafusal fiber) contraction.
ii. There is also simultaneous inhibition of the alpha motor
neuron of antagonistic muscles

46
Q

What happens when the gamma motor neuron is activated?

A

i. This stimulates intrafusal fiber contraction.
ii. If the intrafusal fibers did not contract, the sensory fibers
would not be able to sense a further change in muscle
length since they would be slack

47
Q

What is the effect of muscle spindle activation?

A

Contraction

48
Q

What are the components of the muscle spindle reflex?

A

The reflex has dynamic (immediate) and static (maintains tone- constant contraction) reflex components

49
Q

What happens to the gamma motor neuron when the alpha motor neuron is activated? What does this allow?

A

It is also activated; allows the muscle spindle to maintain sensitivity to changes in muscle length

50
Q

What are golgi tendon organs?

A

Mechanosensative receptors found at the junction of tendons and muscle

51
Q

What are golgi tendon rogans sensitive to?

A

A change in force

52
Q

What kind of reflex is golgi tendon organ?

A

Protective

53
Q

What is the stimulus for the golgi tendon organ?

A

Tendon stretch
1. Tendons stretch in response to
contraction (particularly isometric
—maximal—contractions)
2. Extreme stretch of the tendon will
squeeze the GTO and afferent
neurons will send information into
the spinal cord
a. Stimulates an inhibitory
interneuron.
b. This neuron decreases the
activity of the alpha motor
neuron
c. Skeletal muscle contraction is
decreased (relaxation)

54
Q

What is mastication a mix of?

A

Voluntary, reflex, and central (subconscious) processes

55
Q

What does mastication require?

A

Coordination of muscles controlling lips, tongue and cheeks

56
Q

Voluntary control of mastication is uni/bilateral?

A

Bilateral; although people tend to favor one side of the mouth over the other

57
Q

What is mastication controlled by?

A

Central pattern generator (CPG) of the brainstem, which when stimulated, elicits rhythmic, coordinated activation and inactivation of jaw-closers and jaw openers

58
Q

How is the central pattern generator (CPG) regulated?

A

Input from higher cortical regions via the corticobulbar pathway

59
Q

What is the jaw opening reflex?

A

– Pain inhibits the alpha motor neuron of jaw closing muscles such as when you bite down on your tongue, a metal spoon, with your incisors
– Jaw opens

60
Q

What is the jaw jerk reflex?

A

– Strong tap to the chin stretches the jaw closers
– The jaw closers respond by contraction so the jaw closes
– Stretch reflex

61
Q

How do you determine the force needed to take a bite of something hard?

A
  • CPG starts chewing by activating jaw closing muscles
  • When the jaw closing muscles connect with the food (ex. carrot), they initially meet with resistance:
    – The force of contraction is initially insufficient to
    overcome the load (carrot) – isometric contraction
    – Intrafusal fibers in muscle spindle are still contracting and stretching the muscle spindle so this signals further contraction of jaw closing muscles
  • Constant feedback from the muscle spindle in the jaw closing muscles is sufficient to overcome the load of the carrot — isotonic contraction
62
Q

To crack a nut, a tremendous amount of force is required.
Once the nut cracks, there is potential to damage the intra- oral structures.
What decreases the contraction in these situations?

A

Muscle spindles
– When the nut cracks, the force is now greater than the load (nut).
– At this point, there is more slack in the muscle spindle
which leads to less activation of the muscle (due to decreased alpha/gamma co-activation)

D1 Spring - Physiology Exam 2 (7 decks)

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