Chapter 21: Skeletal Muscle physiology

Question 1

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

Answer 1

one

Question 2

the cell bodies of motor neurons are located in the _____

Answer 2

brain or spinal cord

Question 3

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

Answer 3

motor point

Question 4

motor point

Answer 4

site where a nerve enters a muscle

Question 5

each axonal branch supplies a _____ muscle cell.

Answer 5

single muscle cell

Question 6

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

Answer 6

one

Question 7

motor unit

Answer 7

a motor neuron and all the muscle cells it innervates

Question 8

electrical response to an action potential

Answer 8

depolarization and repolarization

Question 9

physical response to an action potential

Answer 9

contraction and relaxation

Question 10

muscle twitch

Answer 10

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

Question 11

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

Answer 11

muscle twitch

Question 12

muscle twitches three periods

Answer 12

latent period
contraction period
relaxation period

Question 13

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

Answer 13

latent period

Question 14

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

Answer 14

contraction period

Question 15

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

Answer 15

relaxation period

Question 16

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

Answer 16

twitch duration

Question 17

twitch duration

Answer 17

how long a muscle twitch lasts

Question 18

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

Answer 18

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

Question 19

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

Answer 19

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

Question 20

changing the strength of contraction is brought about by _____

Answer 20

force summation

Question 21

force summation occurs in what two ways

Answer 21

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)

Question 22

multiple fiber summation or motor unit recruitment

Answer 22

number of motor units contracting simultaneously

Question 23

frequency summation

Answer 23

frequency of contraction

Question 24

the body produces multiple fiber summation by _____.

Answer 24

increasing the number of motor neurons sending signals to a muscle

Question 25

in a weak contraction only a ____ motor units are active

Answer 25

only a few motor units are active in a weak contraction

Question 26

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

Answer 26

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

Question 27

the body produces frequency summation by increasing what

Answer 27

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

Question 28

frequency

Answer 28

number of signals per second

Question 29

at lower frequencies individual twitches occur when

Answer 29

one after the other

Question 30

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

Answer 30

before the preceding twitch is over

Question 31

why is the second twitch stronger?

Answer 31

because the muscle cells are contracting stronger

Question 32

frequency summation can lead to ___

Answer 32

tetnus

Question 33

tetnus

Answer 33

a sustained contraction

Question 34

tetnus occurs at the frequency where ____________.

Answer 34

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

Question 35

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

Answer 35

because it increases intracellular levels of calcium ions

Question 36

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

Answer 36

calcium ions

Question 37

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

Answer 37

an increase in contraction strength

Question 38

increasing the stenth of stimulation will result in

Answer 38

muscle fiber summation

Question 39

3 ways to increase muscle contraction strength

Answer 39

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

Question 40

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

Answer 40

a fine degree of control over muscle tension

Question 41

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?

Answer 41

with less precise control

Question 42

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?

Answer 42

treppe or staircase effect

Question 43

muscle tone or tonus

Answer 43

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

Question 44

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

Answer 44

true

Question 45

tonus in postural muscles allows what?

Answer 45

allows the body to remain upright

Question 46

the loss of tonus results in…

Answer 46

collapse of the body or fainting

Question 47

fatigue

Answer 47

occurs when a muscle is unable to contract

Question 48

what is one factor that plays a major role in fatigue

Answer 48

increase hydrogen ions

Question 49

an electromyogram is commonly used to….

Answer 49

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

Question 50

displacement

Answer 50

the distance the transducer is moved

Question 51

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

Answer 51

the non dominant hand fatigued faster

Question 52

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

Answer 52

slower

Question 53

which period of muscle twitch had the shortest duration?

Answer 53

latent period

Question 54

which period of the muscle twitch had the longest duration?

Answer 54

relaxation period

Question 55

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

Answer 55

less than

Question 56

what is the frequency of stimulation that caused frequency summation?

Answer 56

5 stimuli per second

Question 57

what is the frequency of stimulation that caused tetanus?

Answer 57

8 stimuli per second