Physio Ex Exercise 2 Activity 3 PDF

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11/4/2020

PhysioEx Exercise 2 Activity 3

PhysioEx Lab Report Exercise 2: Skeletal Muscle Physiology Activity 3: The Effect of Stimulus Frequency on Skeletal Muscle Contraction Name: Dana M. Paolino Date: 4 November 2020 Session ID: session-1732c09f-512a-4172-6a8f-1ae8e9b729e3

Pre-lab Quiz Results You scored 100% by answering 4 out of 4 questions correctly. 1 During a single twitch of a skeletal muscle You correctly answered: maximal force is never achieved. 2 When a skeletal muscle is repetitively stimulated, twitches can overlap each other and result in a stronger muscle contraction than a stand-alone twitch. This phenomenon is known as You correctly answered: wave summation. 3 Wave summation is achieved by You correctly answered: increasing the stimulus frequency (the rate of stimulus delivery to the muscle). 4 Wave summation increases the force produced in the muscle. Another way to increase the force produced by a muscle is to You correctly answered: increase the number of activated motor units.

Experiment Results Predict Questions 1 Predict Question 1: As the stimulus frequency increases, what will happen to the muscle force generated with each successive stimulus? Will there be a limit to this response? Your answer: As the stimulus frequency increases, the muscle force generated by each successive stimulus will increase. There will be a limit to this increase. 2 Predict Question 2: In order to produce sustained muscle contractions with an active force value of 5.2, do you think you will need to increase the stimulus voltage? Your answer: No. Stop & Think Questions https://media.pearsoncmg.com/bc/bc 0media ap/physioex/10/ex2/act3/

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PhysioEx Exercise 2 Activity 3

1 Was there any change in the force generated by the muscle during the second stimulated twitch? You correctly answered: Yes, the second twitch generated more muscle force. 2 Is the total muscle force generated by the higher frequency stimulation greater than the force generated in previous stimulations? You correctly answered: Yes, it is greater than the previous stimulations. 3 Does the force generated by the muscle change with each additional stimulus? You correctly answered: As the stimulus frequency increased, the muscle tension generated by each successive stimulus also increased, and a limiting maximum value was observed. Experiment Data Voltage (v)

Length (mm)

Stimulus

Active Force Passive Force

Total Force

8.5

75

Single

1.83

0.0

1.83

8.5

75

Multiple

2.86

0.0

2.86

8.5

75

Multiple

3.26

0.0

3.26

8.5

75

Multiple

4.52

0.0

4.52

10

75

Multiple

4.31

0.0

4.31

8.5

75

Multiple

5.20

0.0

5.20

Voltage = 8.5 V Single Stimulus Active Force = 1.83

Voltage = 8.5 V Multiple Stimulus Active Force = 2.86 i https://media.pearsoncmg.com/bc/bc 0media ap/physioex/10/ex2/act3/

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Voltage = 8.5 V Multiple Stimulus Active Force = 3.26

Voltage = 8.5 V Multiple Stimulus Active Force = 4.52

Voltage = 10 V Multiple Stimulus https://media.pearsoncmg.com/bc/bc 0media ap/physioex/10/ex2/act3/

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Active Force = 4.31

Voltage = 8.5 V Multiple Stimulus Active Force = 5.20

Post-lab Quiz Results You scored 100% by answering 4 out of 4 questions correctly. 1 Which of the following is not one of the ways that the body can increase the force produced by a skeletal muscle? You correctly answered: application of higher voltages to the whole muscle. 2 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 You correctly answered: treppe. 3 In this experiment the isolated skeletal muscle was repetitively stimulated such that individual twitches overlapped with each other and resulted in a stronger muscle https://media.pearsoncmg.com/bc/bc 0media ap/physioex/10/ex2/act3/

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PhysioEx Exercise 2 Activity 3

contraction than a standalone twitch. This phenomenon is known as You correctly answered: wave summation. 4 Wave summation is achieved by You correctly answered: increasing the rate of stimulus delivery (frequency) to the muscle.

Review Sheet Results 1 What is the difference between stimulus intensity and stimulus frequency? Your answer: Stimulus intensity refers to the strength of the stimulus, whereas stimulus frequency refers to the rate of stimulus delivery to the muscle. 2 In this experiment you observed the effect of stimulating the isolated skeletal muscle multiple times in a short period with complete relaxation between the stimuli. Describe the force of contraction with each subsequent stimulus. Are these results called treppe or wave summation? Your answer: The effect of stimulating the isolated skeletal muscle multiple times in a short period with complete relaxation between the stimuli caused the force of contraction to increase with each subsequent stimulus. The increase was progressive, resembling a step-like increase in force; thus, the results are called treppe (or the staircase effect). 3 How did the frequency of stimulation affect the amount of force generated by the isolated skeletal muscle when the frequency of stimulation was increased such that the muscle twitches did not fully relax between subsequent stimuli? Are these results called treppe or wave summation? How well did the results compare with your prediction? Your answer: I predicted that as the stimulus frequency increased, the muscle force generated by each successive stimulus would also increase with a limit; thus, my prediction was correct. The frequency of stimulation caused the amount of force generated by the isolated skeletal muscle to increase when the frequency of stimulation was increased without muscle twitches fully relaxing between subsequent stimuli. The muscle fibers were already in a partially contracted state when the subsequent stimuli were delivered; thus, the results are called wave summation. 4 To achieve an active force of 5.2, did you have to increase the stimulus voltage above 8.5 volts? If not, how did you achieve an active force of 5.2? How well did the results compare https://media.pearsoncmg.com/bc/bc 0media ap/physioex/10/ex2/act3/

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with your prediction? Your answer: I predicted the stimulus voltage did not need to increases in order to produce sustained muscle contractions with an active force value of 5.2; thus, my prediction was correct. When the stimulus voltage was increased above 8.5 volts (10.0 volts), the active force only reached 4.31. In order to achieve an active force of 5.2, set at a stimulus voltage of 8.5 volts, the stimulus frequency needed to be increased. 5 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. Your answer: Frequency-dependent wave summation and motor unit recruitment are similar as both methods result in an increase of active and total force. However, frequency-dependent wave summation is influenced and achieved by increasing stimulus frequency, whereas motor unit recruitment is influenced and achieved by increasing stimulus intensity. In vivo, the recruitment of additional motor units increases (influences) the total muscle force produced.

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