Bios 255 #2 Twitch Contractions and Summation

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LABORATORY REPORT Activity 2: Twitch Contractions and Summation Name: Ruthann Baker Instructor: Date: March 9, 2014 PREDICTIONS Effect of Muscle Fiber Length on Contraction 1. As muscle fiber length increases: force of contraction increases and then decreases 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.... fiber muscle length, tempeture, frequency of stimulation Effect of Muscle Length on Contraction 1. Dependent Variable... contraction force 2. Independent Variable... muscle fiber length 3. Controlled Variables... frequency of stimulation, temperature, stimulation voltage 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? Motor unit 5. Explain why the temperature of the water bath was 35ºC (95 ºF). Because it is near the normal body temperature of the mouse. 6. At a stimulation frequency of 15 Hz how many stimuli were there per second? 15 pulses 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? 0.084gf 3. How does increasing voltage above threshold stimulus affect force development? When the stimulas voltage is increased an increase within the entire muscle begins to take place. When the voltage is increased beyond the muscle's threshold stimulas, the force generated from the muscle increases.

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