Topics: Skeletal muscle, Muscular system, Neuromuscular junction Pages: 5 (1330 words) Published: November 7, 2013
NAME __Molly Manning__
LAB TIME/DATE ___10/24/13__
Exercise 2
Skeletal Muscle Physiology

The Muscle Twitch and the Latent Period
1. Define the terms skeletal muscle fiber, motor unit, skeletal muscle twitch, electrical stimulus, and latent period. Skeletal muscle fiber-fibers attached to the skeleton that produce muscle tension. Motor unit-consists of the motor neuron and all of the muscle fibers. Skeletal muscle twitch-mechanical response to a single action potential. Electrical stimulus-muscle contractions. Latent period- during a contraction there is a rise in muscle tension.

2. What is the role of acetylcholine in a skeletal muscle contraction? -Trigger action potential.

3. Describe the process of excitation-contraction coupling in skeletal muscle fibers. –The motor end plate produces potential and results in contraction of a single cell.

4. Describe the three phases of a skeletal muscle twitch. 1) Latent period-time lapse between action potential and muscle contraction. 2) Contraction phase-starts at end of latent period and ends when muscle tension peaks. 3) Relaxation phase-starts at peak of tension until the end of the muscle contraction.

5. Does the duration of the latent period change with different stimulus voltages? How well did the results compare with your prediction? – Yes, the results varied in different time amounts.

6. At the threshold stimulus, do sodium ions start to move into or out of the cell to bring about the membrane depolarization? –They start to move out of the cell. A C T I V I T Y 2
The Effect of Stimulus Voltage on Skeletal Muscle Contraction 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? -Contraction occurred with increasing voltage in skeletal muscle. These results matched my prediction.

2. How is this change in whole-muscle force achieved in vivo -Changing the stimuli and collecting and recording data.

2. What happened in the isolated skeletal muscle when the maximal voltage was applied? -The muscle contracted

The Effect of Stimulus Frequency on Skeletal Muscle Contraction 1. What is the difference between stimulus intensity and stimulus frequency? -Stimulus frequency is the rate of stimulus delivery to the muscle. –Stimulus intensity is the action potential by the amplitude.

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? -They are Treppe

3. The frequency of stimulation affected 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? -These are called Wave summation. This did not match the results I predicted.

4. 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 5.2 g? How well did the results compare with your prediction? -you had to increase the stimulus to above 8.5 volts. The results matched my prediction.

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. -They are different forces. –They were achieved in the experiment by adding stimuli and observing and tracing results. – Each is achieved in vivo by setting the voltage, adding stimuli,...
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