Physio EX-02-02 PDF

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Name: Lily Rosenblum Exercise 2: Skeletal Muscle Physiology: Activity 2: The Effect of Stimulus Voltage on Skeletal Muscle Contraction Lab Report Pre-lab Quiz Results You scored 100% by answering 4 out of 4 questions correctly. 1. Skeletal muscle fibers are innervated (stimulated) by You correctly answered: c. motor neurons. 2. A single action potential propagating down a motor axon results in You correctly answered: d. a single action potential and a single contractile event in the muscle fibers it innervates. 3. In resting skeletal muscle, calcium is stored in You correctly answered: c. the sarcoplasmic reticulum. 4. During the latent period for an isometric contraction You correctly answered: c. the cellular events involved in excitation-contraction coupling occur.

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Experiment Results Predict Question: Predict Question: As the stimulus voltage is increased from 1.0 volt up to 10 volts, what will happen to the amount of active force generated with each stimulus? Your answer : a. The active force will continually increase. Stop & Think Questions: What do you see in the active force display when the stimulus voltage is set to 0.0, and why does this observation make sense? You correctly answered: a. 0.00 g; there was no activation of skeletal muscle fibers by this stimulus. What is the lowest stimulus voltage that induces active force in the skeletal muscle? You correctly answered: b. threshold voltage 6. Enter the threshold voltage for this experiment in the field below and then click Submit Data to record your answer in the lab report You answered: .8 volts 12. Enter the maximal voltage for this experiment in the field below and then click Submit Data to record your answer in the lab report. You answered: 8.5 volts Experiment Data: Voltage 0.0

Length 75

Active Force 0.0

0.2 0.3 0.4 0.5 0.6 0.7

75 75 75 75 75 75

0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0

0.8 1.0 1.5 2.0 2.5 3.0

75 75 75 75 75 75

0.02 0.15 0.43 0.66 0.87 1.04

0.0 0.0 0.0 0.0 0.0 0.0

0.02 0.15 0.43 0.66 0.87 1.04

3.5 4.0 4.5 5.0 5.5 6.0

75 75 75 75 75 75

1.19 1.32 1.42 1.51 1.59 1.65

0.0 0.0 0.0 0.0 0.0 0.0

1.19 1.32 1.42 1.51 1.59 1.65

6.5 7.0 7.5 8.0

75 75 75 75

1.70 1.74 1.78 1.81

0.0 0.0 0.0 0.0

1.70 1.74 1.78 1.81

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Passive Force 0.0

Total Force 0.0

Voltage 8.5 9.0 9.5

Length 75 75 75

Active Force 1.82 1.82 1.82

10.0

75

1.82

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Passive Force 0.0 0.0 0.0 0.0

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Total Force 1.82 1.82 1.82 1.82

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Post-lab Quiz Results You scored 100% by answering 6 out of 6 questions correctly. 1. Motor unit recruitment refers to You correctly answered: a. an increase in the number of active muscle fibers to increase the force developed in a muscle. 2. Active tension (or force) in a skeletal muscle fiber results from You correctly answered: a. activation of cross bridge cycling via increased intracellular calcium levels. 3. The ________ is the minimal stimulus needed to cause a depolarization of the muscle plasma membrane (sarcolemma). You correctly answered: d. threshold voltage 4. By definition, the ________ is the amount of stimulus required to successfully recruit all the muscle fibers into developing active force. You correctly answered: c. maximal voltage 5. Why was a maximal voltage observed in this experiment? You correctly answered: b. At the maximal voltage, all the muscle fibers contained in this muscle are depolarized and they all develop active force (that is, they were all successfully recruited). 6. 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? You correctly answered: c. The electrical stimulus mimics acetylcholine release at a neuromuscular junction

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Review Sheet Results 1. Describe the effect of increasing stimulus voltage on isolated skeletal muscle. Specifically, what happened to the muscle force generated with stronger electrical stimulations and why did this change occur? How well did the results compare with your prediction? Your answer: By increasing the stimulus voltage on the skeletal muscle it makes it so that the total force generated by the muscle also increases. My results confirmed my prediction but reached a threshold of 8.5 volts. 2. How is this change in whole-muscle force achieved in vivo? Your answer: Basically the change in the whole-muscle force was achieved "in vivo" where additional motor units were recruited to increase the total muscle force produced. However for the experiment to be succesful, at the beginning, the electric current must go beyond the threshold. Once the stimulus voltage went beyond the threshold, it created whole muscle force. As the force gets stronger with the higher stimulus voltage until it reached a maximum for 8.5. 3. What happened in the isolated skeletal muscle when the maximal voltage was applied? Your answer: All of the muscle fibers in the skeletal muscle became depolarized and resulted in making an active force. All of the fibers were needed to participate to make a maximal voltage occur.

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