Lab 8 Muscle worksheet PDF

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From Dr. Garrison...

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BIO 270 Lab 8: Muscle worksheet

score ______ /10

Instructions: Type your answers directly on this document and print out when completed. Names: 1. Exercise 2: Twitch response and recruitment a. Copy the table for this exercise (in Lab Tutor) by clicking on the spreadsheet icon in the upper right hand corner of the table that contains the data for contraction force as a function of stimulus strength in LabTutor. Paste the data into excel and produce a scatter plot (Figure 1) of force as a function of stimulus strength. Paste the resulting figure here and provide an appropriate caption beneath the figure. (1 pt)

b. You should not have seen a measurable twitch at a stimulus of 0 mA. What does this tell you about the number of muscle fibers contracting at this stimulus current? (0.25 pt) At 0 mA, muscle fibers didn’t contract because the stimulus wasn’t strong enough to hit threshold right away which is why there was no change until it hits threshold. The stronger the stimulus, the more motor neurons are recruited which leads to a stronger contraction. c. What was the smallest current required to produce a contraction (the threshold current)? What proportion of the fibers in the muscle do you think were contracting to produce this minimal response? (0.25 pt) The muscles began twitching at 4 mA because the threshold was reached to generate an action potential. Just a few of the muscle fibers were contracting. d. What was the smallest current required to produce the maximum (largest) contraction? What proportion of the fibers in the muscle do you think were contracting to produce this maximal response? (0.25 pt) The maximum contraction was produced at 8 mA. 100% of the fibers in the muscle were contracting to produce this maximal response. e. Physiologically, why does varying the stimulus strength affect the twitch force? (1 pt) Increasing motor unit recruitment occurs by increasing the stimulus magnitude (strength of stimulus). When the stimulus strength increases, more nerve fibers are stimulated, and the muscle

contractions are stronger (graded strength). Innervating more motor units increases the number of muscles contracting which increases the twitch force.

2. Exercise 3: Single twitch a. Copy the table for this exercise (in Lab Tutor) by clicking on the spreadsheet icon in the upper right-hand corner of the table. Paste into Excel and adjust column widths as necessary, then select the entire table and from the Borders menu, select All Borders. Paste this formatted table (Table 1) into the space below. Be sure to enter appropriate units. (0.5 pt) Table 1: Various Parameters Associated with Single Twitch Parameter

Value

Contraction Strength

0.0432 FU

Latent Period

0.1380 sec

Contraction Period

0.0700 sec

Relaxation Period

0.2990 sec

Contraction Velocity

0.6171 FU/sec

Relaxation Velocity

0.1445 FU/sec

b. Calculate the contraction velocity here (show all work). (0.25 pt) 0.0432 FU / 0.0700 sec = 0.6171 FU/sec c. Calculate the relaxation velocity here (show all work). (0.25 pt) 0.0432 FU / 0.2990 sec = 0.1445 FU/sec d. Give a physiologically sound explanation for any differences observed between contraction and relaxation velocities. If no differences were observed, which do you think should be slower and why? (1 pt) Contraction is faster than relaxation because calcium is released faster than it is being pumped back into the SR by the Ca2+ ATPase Pump. 3. Exercise 4: Summation a. What was the frequency of stimulation at the beginning of summation? Be sure to include the units and show your calculations. (0.5 pt)

f=1/i f = 1 / 0.125s f = 8 stimuli/ second b. Explain the mechanism of summation. (1 pt) Motor recruitment can be increased by increasing stimulus frequency (sequential recruitment). Summation occurs as a result of muscle fibers undergoing a second action potential before the muscle is able to relax. The second twitch builds upon the first twitch, resulting in a greater response. When the first amount of calcium is released it triggers a contraction however before all of it can be pumped back into the SR another stimuli occurs which triggers the release of even more calcium that adds to the previous amount of calcium released, causing a stronger contraction. 4. Exercise 5: Tetany a. Copy the table for this exercise (in Lab Tutor) by clicking on the spreadsheet icon in the upper right-hand corner of the table. Paste into Excel and remove data concerning relaxation. Adjust column widths as necessary, then select the entire table and from the Borders menu, select All Borders. Paste this formatted table into the space below. Be sure to enter appropriate units. (0.5 pt) Table 2: Percent Increase from a Single Twitch to the Magnitude at Tetany Parameter

Value

Force of a single twitch

0.007 FU

Magnitude at Tetany

0.0175 FU

Percent increase

150%

b. Calculate the percent increase in force here (show all work). (0.25 pt) Percent Increase = [(Magnitude at Tetany - Force of single twitch) / Force of single twitch] x 100 % Increase = [(0.0175 FU - 0.007 FU) / 0.007 FU] x 100 % Increase = 150 c. You use a short period of electrical stimuli to observe muscle fibers contracting continuously (tetany). Chemical agents can cause tetanus by interfering with the motor neurons. These agents include a toxin produced by the soil bacterium Clostridium tetani. One of the symptoms of these agents is called spastic paralysis. Explain in your own words why these agents would be a bad thing for you and your muscles. (0.5 pt) Agents that produce tetanus are dangerous for people and their muscles because it causes chronic muscle spasms which can lead to death. Tetanus makes it hard for people to control and relax their muscles making it impossible to open their mouth or swallow. The diaphragm is the muscle that divides a person’s chest into two cavities and creates the pressure difference to fill the lungs with oxygen. Tetanus of that muscle, inhibits relaxation, resulting in the person not being able to breath because they cannot relax the muscle and exhale resulting in asphyxiation which is deadly.

5. Exercise 5a: Muscle fatigue a. Copy the table for this exercise (in Lab Tutor) by clicking on the spreadsheet icon in the upper right-hand corner of the table. Paste into Excel and remove all data except those concerning relaxation. Adjust column widths as necessary, then select the entire table and from the Borders menu, select All Borders. Paste this formatted table into the space below. Be sure to enter appropriate units. (0.5 pt) Table 3: The Effect of Fatigue on Relaxation Time Parameter

Value

Recovery time after tetany of fresh muscle

0.4 sec

Recovery Time from Fatigue

1.22 sec

b. Which relaxed faster, the muscle before exercise or the muscle after exercise? Explain why this happened with good physiological reasons as to why the relaxation times should have been different (include the mechanism for relaxation). (1 pt) The muscle relaxed faster before exercise. When a muscle in contracted or used for an extended period of time, the ATP supply is depleted. This depletion of ATP is called “muscle fatigue”. Muscle fatigue interferes with the reuptake of calcium, which will slow the rate that another muscle relaxation will occur. c. Since your body operates by means of action potentials which are all-or-none, how does your body mimic the same effect of increasing current? (0.5 pt) The body mimics the same effect of increasing current through spatial summation, which happens when the brain activates multiple motor units being recruited at the same time to increase the force of contraction.

d. How does your body mimic the same effect of increasing stimulation frequency? (0.5 pt) Your brain can send action potentials down to cause contraction at a faster rate....