Chapter 21: Skeletal Muscle physiology Flashcards Preview

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Flashcards in Chapter 21: Skeletal Muscle physiology Deck (57)
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1
Q

each skeletal muscle is innervated by at least ____ motor nerve which contains axons of up to hundreds of motor neurons.

A

one

2
Q

the cell bodies of motor neurons are located in the _____

A

brain or spinal cord

3
Q

the site where a nerve enters a muscle is called the _____

A

motor point

4
Q

motor point

A

site where a nerve enters a muscle

5
Q

each axonal branch supplies a _____ muscle cell.

A

single muscle cell

6
Q

although a skeletal muscle is innervated by several neurons and the axonal branches of each neuron go to different muscle cells, each cell is usually innervated by only ____ motor neuron

A

one

7
Q

motor unit

A

a motor neuron and all the muscle cells it innervates

8
Q

electrical response to an action potential

A

depolarization and repolarization

9
Q

physical response to an action potential

A

contraction and relaxation

10
Q

muscle twitch

A

a motor unit’s physical response to a single stimulus from its neuron

11
Q

a motor unit’s physical response to a single stimulus from its neuron is called a ___

A

muscle twitch

12
Q

muscle twitches three periods

A

latent period
contraction period
relaxation period

13
Q

the time between the arrival of a stimulus and the beginning of muscle shortening. during this time excitation contraction coupling occurs. once the cross bridges become active, tension begins to develop in the muscle

A

latent period

14
Q

time between the beginning of muscle shortening and the development of peak tension

A

contraction period

15
Q

time between the development of peak tension and the return of the muscle to its resisting length

A

relaxation period

16
Q

the number of fast-twitch fibers in a muscle determines ___

A

twitch duration

17
Q

twitch duration

A

how long a muscle twitch lasts

18
Q

an ocular muscle is composed of mostly ____ twitch fibers and has a twitch duration of around _____ milliseconds

A

fast twitch fibers and has a twitch duration of around 10 milliseconds

19
Q

the soleus muscle (a postural muscle in the lower leg) has a lot of _____ fibers and its twitch duration is around ______ milliseconds

A

slow twitch fibers and has a twitch duration of around 200 milliseconds

20
Q

changing the strength of contraction is brought about by _____

A

force summation

21
Q

force summation occurs in what two ways

A
  1. by increasing the number of motor units contracting simultaneously (called multiple fiber summation or motor unit recruitment)
  2. by increasing the frequency of contraction (called frequency summation)
22
Q

multiple fiber summation or motor unit recruitment

A

number of motor units contracting simultaneously

23
Q

frequency summation

A

frequency of contraction

24
Q

the body produces multiple fiber summation by _____.

A

increasing the number of motor neurons sending signals to a muscle

25
Q

in a weak contraction only a ____ motor units are active

A

only a few motor units are active in a weak contraction

26
Q

in a stronger contraction more motor units are sending signals resulting in

A

resulting in more motor units being active or more muscle cells are contracting

27
Q

the body produces frequency summation by increasing what

A

by increasing the frequency (number of signals per second) at which motor neurons send signals

28
Q

frequency

A

number of signals per second

29
Q

at lower frequencies individual twitches occur when

A

one after the other

30
Q

as frequency increases there comes a point when another twitch occurs when

A

before the preceding twitch is over

31
Q

why is the second twitch stronger?

A

because the muscle cells are contracting stronger

32
Q

frequency summation can lead to ___

A

tetnus

33
Q

tetnus

A

a sustained contraction

34
Q

tetnus occurs at the frequency where ____________.

A

the successive contractions become so rapid they fuse together so there is no relaxation between stimuli

35
Q

one reason a higher frequency of stimulation causes muscle cells to contract stronger is

A

because it increases intracellular levels of calcium ions

36
Q

it is the binding of ____ ions to troponin that makes the binding sites available

A

calcium ions

37
Q

an increased level of calcium reults in more binding sites available to participate in contraction which, in turn, causes what

A

an increase in contraction strength

38
Q

increasing the stenth of stimulation will result in

A

muscle fiber summation

39
Q

3 ways to increase muscle contraction strength

A
  1. muscle fiber summation
  2. frequency summation and tetnus
  3. treppe (staircase effect)
40
Q

when a muscle has small motor units recruitment results in only a small increase in contraction strength. this allows what?

A

a fine degree of control over muscle tension

41
Q

a muscle with large motor units results in a large increase in the amount of tension developed. such muscles can produce powerful contraction but with what?

A

with less precise control

42
Q

when a well rested muscle is stimulated several times, there will be a slight increase in strength during the first few contractions. what is this called?

A

treppe or staircase effect

43
Q

muscle tone or tonus

A

continual activity of some motor units maintains a low level of tension

44
Q

true or false: even in a relaxed muscle some motor units are active

A

true

45
Q

tonus in postural muscles allows what?

A

allows the body to remain upright

46
Q

the loss of tonus results in…

A

collapse of the body or fainting

47
Q

fatigue

A

occurs when a muscle is unable to contract

48
Q

what is one factor that plays a major role in fatigue

A

increase hydrogen ions

49
Q

an electromyogram is commonly used to….

A

determine the intensity and frequency of a muscle electrical response under varying conditions as well as which muscle are active during specific movements

50
Q

displacement

A

the distance the transducer is moved

51
Q

is there any difference between hands in the amount of time it took for fatigue to occur?

A

the non dominant hand fatigued faster

52
Q

a muscle with a normal blood supply with fatigue ______ than a muscle with no blood supply

A

slower

53
Q

which period of muscle twitch had the shortest duration?

A

latent period

54
Q

which period of the muscle twitch had the longest duration?

A

relaxation period

55
Q

the strength of contraction of a muscle twitch was _____ the strength of contraction of tetanus

A

less than

56
Q

what is the frequency of stimulation that caused frequency summation?

A

5 stimuli per second

57
Q

what is the frequency of stimulation that caused tetanus?

A

8 stimuli per second

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