PowerPhys:Activity 2 Twitch Contractions and Summation Essay

1520 Words Feb 2nd, 2014 7 Pages
LABORATORY REPORT
Activity 2: Twitch Contractions and Summation

PREDICTIONS
Effect of Muscle Fiber Length on Contraction
1. As muscle fiber length increases: contraction force increases, becoming maximum at an optimal length, then decreasing at longer lengths.
Effect of Stimulation Frequency on Contraction
2. As the frequency of stimulation increases, the force of contraction: increases.

MATERIALS AND METHODS
Measurement of Threshold Stimulus
1. Dependent Variable: contraction force.
2. Independent Variable: stimulation voltage
3. Controlled Variables: temperature, frequency of stimulation and muscle fiber length.
Effect of Muscle Length on Contraction
1. Dependent Variable: contraction force.
2. Independent Variable:
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Maximum force occurs when all the motor units of a muscle are stimulated and all muscle fibers are contracting. After reaching this optimal threshold, there is a voltage above which any further increase in stimulation intensity results in no further increase in force generation. Thus a stimulus to the muscle greater than the maximal stimulus (voltage) does not produce a greater force.
3. Explain why force of contraction changes with muscle fiber length. There is a muscle length-tension relationship between the length of the fiber and the force produced by that fiber at that length. When an isolated muscle fiber is stretched to the point of minimal or maximal overlap of actin and myosin and then stimulated to contract, the force of contraction measured is minimal. On the other hand, if an isolated muscle fiber is stimulated to contract when there is optimal overlap of actin and myosin the force produced will be maximal.
4. Compare the maximum force generated when stimulation frequency was increased with the maximum force generated at threshold stimulus. In your opinion, which experiment resulted in the highest level of intracellular calcium? The maximum force generated, when stimulation frequency was increased, was 0.227 gf (for
60Hz) vs. the maximum force generated at threshold stimulus was 0.084 gf (for 400 mV).
The experiment that resulted in the highest level of intracellular Ca was when stimulation

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