Exam 3- skeletal muscle phys

Question 1

skeletal muscles are composed of hundreds to thousands of individual cells called [a] [b] which produce muscle tension

Answer 1

muscle fibers

Question 2

an action potential in a motor neuron triggers the release of ________ from its terminal

Answer 2

aceytlcholine

Question 3

a motor unit consists of a [a][b] and all of the muscle fibers it innervates

Answer 3

motor neuron

Question 4

the motor neuron and muscle fiber intersect at what is called the [a] [b]

Answer 4

neuromuscular junction

Question 5

The graded depolarization in the skeletal muscle fiber that is elicited in response to one action potential from the motor neuron is called

Answer 5

EPP (end-plate potential)

Question 6

the end-plate potential is a

Answer 6

graded potential

Question 7

one contractile response to a single action potential is a [a][b]

Answer 7

muscle witch

Question 8

the length of time that elapses the peak of tension muscle tension to the end of muscle contraction is the [a][b]

Answer 8

relaxation phase

Question 9

A sufficiently strong electrical stimulus applied to an isolated, mounted skeletal muscle induces the development of muscle force, or muscle tension. Which of the following statements concerning this observation is true

Answer 9

the electrical stimulus mimics acetylcholine release at a Neuromuscular junction

Question 10

by definition the ________ voltage is the amount of stimulus required to successfully recruit ALL the muscle fibers into developing active force

Answer 10

maximal

Question 11

In Pex 2-1 you changed the stimulus voltage

did this alter the duration of the latent perio

Answer 11

no changing the stimulus voltage did not change the latent period

Question 12

the [a] [b] is the smallest stimulus required to induce an action potential in a muscle fiber’s plasma membrane or sarcolemma

Answer 12

threshold voltage

Question 13

the threshold voltage for this experiment in PEX 2 act 2 was______volts

Answer 13

0.8

Question 14

What occurs during the latent period of isometric contractions?

Answer 14

All the steps of excitation-contraction coupling occur

Question 15

the lowest voltage that produced the peak force (the maximal voltage) in exercise 2 PEX 2 was_______volts

Answer 15

8.5

Question 16

in exercise 2 PEX 2 as the stimulus voltage increased from 1.0 volt to 10 volts

Answer 16

the active force increased as the simulus voltage increased but then plateaud at a maximal value

Question 17

the maximal active force in exercise 2 PEX 2 was_______g

Answer 17

1.82

Question 18

contraction phase

Answer 18

myofilaments utilize the cross-bridge cycle

Question 19

latent phase

Answer 19

calcium is released into the sarcoplasmic reticulum

Question 20

relaxation phase

Answer 20

crossbridges between actin and myosin are released

Question 21

the reason a maximal voltage was observed is that

Answer 21

at the maximal voltage, all the muscle fibers contained in this muscle are depolarized and they all develop active force

Question 22

a weak muscle contraction

Answer 22

implies that few motor units are activated

Question 23

In activity PEX 2 exercise 2 the simulations rely on indirect stimulation of the skeletal muscle by an electrode. This differs from In VITRO

Answer 23

because in vivo each muscle fiber receives direct stimulation via Ach from a nerve ending

Question 24

motor unit recruitment refers to

Answer 24

an increase in the # if active muscle fibers to increase the force developed in a muscle

Question 25

a decline in a skeletal muscle’s ability to maintain a constant level of force or tension after prolonged, repetitive stimulation is ______

Answer 25

fatigue

Question 26

when a skeletal muscle is stimulated repeatedly, such that the stimuli arrive one after another within a short period of tie, muscle twitches can overlap with each other and result in a stronger muscle contracton than a stand-alone twitch. This phenomenon is [a][b]

Answer 26

wave summation

Question 27

the progressive increase in force generated when a muscle is stimulated in succession, such that muscle twitches follow one another closely with each successive twitch peaking slightly higher than one before is ________

Answer 27

treppe

Question 28

Wave summation is achieved by increasing the stimulus______

Answer 28

frequency

Question 29

When a muscle receives a stimulus frequency that causes NON-overlapping twitches to follow each other closely in time such that the peak tension of each twitch rises in a stepwise fashion up to a plateau value, the result is known as

Answer 29

treppe

Question 30

Which of the following is NOT one of the ways that the body can increase the force produced by a skeletal muscle

Answer 30

application of higher voltages to the whole muscle

Question 31

In Activity 3 you repeated a stimulus as the relaxation phase started what happened to the muscle force generated with each successive stimulus?

Answer 31

as the stimulus frequency increased the muscle force generated by each successive stimulus increased there is a limit to the increase

Question 32

isolated skeletal muscle was repetitively stimulated such that individual twitches overlapped with each other and resulted in a stronger muscle contraction than a stand alone twitch. This phenomenon is

Answer 32

wave summation

Question 33

in activity 3 you elicited a second stimulus as soon as the muscle force returned to baseline from the first stimulus

select the true statement

Answer 33

the 2nd twitch generated more muscle force

Question 34

Wave summation is achieved by

Answer 34

increasing the rate of stimulus delivery (frequency) to the muscle

Question 35

To achieve an active force of 5.2 g did you have to increase the stimulus voltage above 8.5 volts? If not how did you achieve an active force of 5.3 g? How well did the results compare with your prediction?

Answer 35

I did not increase the stimulus above 8.5 volts. I achieved the active force of 5.3g by repeatedly stimulating the muscle continuously through the contraction phase. My results proved to be consistent with the prediction I made that voltage would not have to be increased

Question 36

What is the difference between stimulus intensity and stimulus frequency

Answer 36

Stimulus intensity is related to the amount of voltage being applied to the muscle where stimulus frequency is related the the number of times the muscle is stimulated by the voltage in a time frame.

Question 37

compare and contrast frequency-dependent wave summation with motor unit recruitment (previously observed by increasing the stimulus voltage) How are they similar: How was each achieved in the experiment: Explain how each is achieved in vivo?

Answer 37

Frequency- dependent wave summation is dependent upon stimulation by the nervous system. The motor recruitment depends on the number of motor fibers available. They both work to increase force production by the muscle. Wave summation depends on the frequency of the stimulation whereas motor unit recruitment depends on the intensity of the stimulus- more motor units recruited for stronger stimulus.

Question 38

n the introduction to exercise 2 activity the major factor causing fatigue, in the case of high-intensity exercise,were listed as

Answer 38

accumulations of lactic acid
accumulations of ADPi
accumulations of Pi

Question 39

during fatigue

Answer 39

the # of active cross bridges begins to decline although the rate of stimulus delivery remains constant

Question 40

if a rest period is imposed on active skeletal muscle

Answer 40

the development of fatigue will be delayed

Question 41

tetanus refers to

Answer 41

sustained muscle tension due to repetitive stimuli

Question 42

during cross bridge cycling in skeletal muscle force is created by the

Answer 42

power stroke of the myosin heads

Question 43

maximal active tension will be produced in a skeletal muscle fiber when

Answer 43

the fiber is at its resting length

Question 44

what key variable was studied in activity 6 in an isometric contraction of skeletal muscle

Answer 44

starting muscle length

Question 45

xplain why active force varies with the muscle’s starting length relative to its resting length

Answer 45

active force depends on the number of crossbridge cycles. At the resting length the maximum number of myosin heads can attach to actin

Question 46

over what length in activity 6 did you start to see passive force

Answer 46

over 80 mm

Question 47

explain what effect a heavier load had on the latent period and why it had this effect

Answer 47

heavier loads increased the latent period

more force is required to move a heavier load so more fibers had to be recruited. This takes more time

Question 48

during an isotonic contraction there is a [a][b] during which there is a rise in muscle tension but no observable movement of the weight

Answer 48

latent period

Question 49

as the load on the muscle increased what happened to the latent period, the shortening velocity, the distance the weight moved and the contraction duration

Answer 49

the latent period increased
the shortening velocity decreased
the distance moved decreased
the contract duration decreased

Question 50

which takes more time: 10 repititions of 10kg or 10 repititions of 5kg?

Answer 50

the 10kg repititon would have a longer latent period-start more slowly, and lower velocity thus longer duration