PowerPhys:Activity 2 Twitch Contractions and Summation Essay

1499 Words Jan 12th, 2014 6 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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60 Hz.
10. What was the maximum force generated in this experiment? 0.277 gf
11. How does increasing stimulation frequency affect force production? The tension produced during a sustained contraction is greater than that produced by a single twitch.
The more stimuli per second, the greater the force generated by the muscle due to a sustained contraction. Muscle tension depends on the frequency of stimulation of motor units and the number of motor units stimulated. By increasing the frequency of muscle stimulation, a sustained force generation is being produced.

DISCUSSION
1. Explain why muscle contraction does not occur below threshold stimulus. It does not occur below the threshold stimulus because it needs a minimal voltage that can induce an action potential. The stimulus causes depolarization in either the nerve or muscle. If depolarization doesn’t reach the threshold, then the nerve or the muscle will not generate that necessary action potential to cause a muscle contraction. A subthreshold stimulus does not cause an action potential because it does not bring the membrane potential to threshold.
2. The maximum stimulation voltage used was 500 mV. If the stimulation voltage was increased to 600mV volts, would the force of contraction decrease, stay the same, or increase? Explain your choice. The force of contraction will decrease. Once the stimulation voltage rises above threshold, force generation

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