PowerPhys:Activity 2 Twitch Contractions and Summation

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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: muscle fiber length.
3. Controlled Variables: temperature, stimulation voltage, frequency of stimulation.
Effect of Stimulation Frequency on Contraction
1. Dependent Variable: contraction force.
2. Independent Variable: frequency of stimulation.
3. Controlled Variables: temperature, stimulation voltage.
4. What structure was stimulated to cause a muscle contraction? The motor unit was stimulated. 5. Explain why the temperature of the water bath was 35ºC (95 ºF). The water bath was 35ºC because is near the mouse’s normal body temperature.
6. At a stimulation frequency of 15 Hz how many stimuli were there per second?
There are 15 pulses (stimuli) per second.

RESULTS
See Table 4: Measurement of Threshold Stimulus
See Graph: Effect of Stimulation Value on Twitch Contraction Force
1. What is the threshold stimulus? 400mV.
2. What is the maximum force generated at the threshold stimulus? The maximum force generated was 0.084 gf.
3. How does increasing voltage above threshold stimulus affect force development?
The stimulus is measured in volts, and its role is to cause depolarization of the muscle fiber or the nerve. A minimum voltage is needed in order to induce an action potential.
This minimal voltage is called a

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