Skeletal Muscle Physiology Physioex Exercise 2

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I have only listed the questions that required answers that are a part of this exercise.

A C T I V I T Y 1
Identifying the Latent Period
How long is the latent period? _____2.78____ msec

Note: If you wish to print your graph, click Tools on the
menu bar and then click Print Graph.

5. Increase or decrease the stimulus voltage and repeat the
experiment. (Remember that you can clear the tracings on the screen at any time by clicking Clear Tracings.) Record your
data here:

Stimulus Latent
voltage: ____4.0____ V period: ____2.78____ msec

Stimulus Latent
voltage: ____3.0____ V period: ___2.78_____ msec

Stimulus Latent
voltage: ___10.0_____ V period: ____2.78____ msec

Does the latent period change with different stimulus
voltages? ____No____

A C T I V I T Y 2
Identifying the Threshold Voltage
2. Click Stimulate. What do you see in the Active Force
display? 0.00

7. Print out the graph(s) that you see on the oscilloscope
screen by clicking Tools at the top of the screen and then selecting Print Graph.

What is the threshold voltage? ____0.8____ V

How does the graph generated at the threshold voltage differ from the graphs generated at voltages below the threshold?
There is no movement below the threshold. However, there is a tiny increase between 10 and 50 of the force line.

A C T I V I T Y 3
Effect of Increases in
Stimulus Intensity

3. Observe your tracings. How did the increases in voltage
affect the peaks in the tracings?
They increased with each increase in voltage.

How did the increases in voltage affect the amount of active force generated by the muscle?
The force increased.

What is the voltage beyond which there were no further increases in active force? Maximal voltage: ____8.5____ V

Why is there a maximal voltage? What has happened to the
muscle at this voltage? Keep in mind that the muscle we are
working with consists of many individual muscle fibers.
For the prevention of damage to the muscle. The muscle fibers cannot contract any further.

An individual muscle fiber follows the all-or-none principle— it will either contract 100% or not at all. Does the muscle we are working with exhibit the all-or-none principle? Why or
why not?
No. The muscle will contract only if there is enough active force.

4. If you wish, you may view a summary of your data on a
plotted data grid by clicking Tools and then Plot Data.

5. Click Tools → Print Data to print your data. ■

A C T I V I T Y 4
Treppe

3. Click Single Stimulus once. You will watch the trace
rise and fall. As soon as it falls, click Single Stimulus again. Watch the trace rise and fall; when it falls, click Single Stimulus a third time.

What do you observe?
The peak rose higher each time. It created staircase-like tracings that showed latent, contraction, and relaxation phases of treppe.

A C T I V I T Y 5
Summation

2. Click on the Single Stimulus button and observe the oscilloscope screen.

What is the active force of the contraction? ___1.83____ gms

3. Click on the Single Stimulus button once. Watch the
trace rise and begin to fall. Before the trace falls completely, click Single Stimulus again. (You may want to simply click
Single Stimulus twice in quick succession in order to
achieve this.)

What is the active force now? ___3.26____ gms.

4. Click on Single Stimulus and allow the graph to rise and
fall before clicking Single Stimulus again.

Was there any change in the force generated by the muscle?
Yes, the force decreased.

5. Click on Single Stimulus and allow the graph to rise, but not fall, before clicking Single Stimulus again.

Was there any change in the force generated by the muscle?
Yes. (3.03 grams)

Why has the force changed?
The muscle was stimulated at different intervals.

6. Decrease the voltage on the stimulator and repeat this
activity.

Do you see the same pattern of changes in the force
generated? Yes.

7. Next,...
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