Laboratory Report

Predictions

Effect of Muscle Fiber Length on Contraction

Effect of Stimulation Frequency on Contraction

Materials and Methods

Measurement of Threshold Stimulus

Effect of Muscle Length on Contraction

Effect of Stimulation Frequency on Contraction

What structure was stimulated to cause a muscle contraction?
Explain why the temperature of the water bath was 35ºC (95 ºF).
At a stimulation frequency of 15 Hz how many stimuli were there per second?

Results

Measurement of Threshold Stimulus
	Voltage (mV)
	100 mV	200 mV	300 mV	400 mV	500 mV
Maximum Force (gf) (Motor unit 1)

Effect of Stimulation Value on Twitch Contraction Force

What is the threshold stimulus?
What is the maximum force generated at the threshold stimulus?
How does increasing voltage above threshold stimulus affect force development?

Muscle Length and Contraction Force
Muscle Length (mm)	6.5	7.0	7.5	8.0	8.5	9.0	9.5	10.0	10.5
Maximum Force (gf) (Motor unit 1)


Average

Effect of Muscle Fiber Length on Contraction Force

What was the average force of contraction at a muscle length of 7.0 mm?
What was the optimal muscle length (muscle length that generated the maximum force)?
What was the maximum force generated at optimal length?
How does increasing muscle fiber length affect force of muscle contraction?

Stimulation Frequency and Contractile Force
	Stimuli per second
	7.5	15	30	45	60
Maximum Force (gf) (Motor unit 1)

Effect of Stimulation Frequency on Contraction Force

What was the force of contraction at a stimulation frequency of 22.5?
At what frequency of stimulation was the maximum force generated?
What was the maximum force generated in this experiment?
How does increasing stimulation frequency affect force production?

Discussion

Explain why muscle contraction does not occur below threshold stimulus.
When stimulation voltage was increased above threshold, did the force of contraction increase, decrease, or stay the same? Explain why this occurred.
Explain why force of contraction changes with muscle fiber length.
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?
Explain why differences in intracellular calcium levels result in differences in force production.
In the experiment Effect of Stimulation Frequency on Contractile Force, why was muscle fiber length set to optimal length?
Restate your predictions that were correct and give data from your experiment that support them. Restate your predictions that were not correct and correct them with supporting data from your experiment.

Application

Botulinum toxin is taken up by axon terminals and inhibits the ability of a motor neuron to stimulate a skeletal muscle motor unit to contract by preventing the release of acetylcholine from the axon terminal. Explain how this prevents skeletal muscle contraction.
Explain why injecting Botox (derived from botulinum toxin) into a superficial facial muscle reduces the appearance of deep facial wrinkles called muscle lines. Hint: Superficial facial muscles are attached at one end to skin.

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Twitch Contractions and Summation

Effect of Muscle Fiber Length on Contraction 1. As muscle fiber length increases undefined Effect of Stimulation Frequency on Contraction 2. As the frequency of stimulation increases, the force of contraction: undefined Measurement of Threshold Stimulus 1. Dependent Variable undefined 2. Independent Variable undefined 3. Controlled Variables undefined; undefined; undefined Effect of Muscle Length on Contraction 1. Dependent Variable undefined 2. Independent Variable undefined 3. Controlled Variables undefined; undefined; undefined Effect of Stimulation Frequency on Contraction 1. Dependent Variable undefined 2. Independent Variable undefined 3. Controlled Variables undefined; undefined 4. What structure was stimulated to cause a muscle contraction? undefined 5. Explain why the temperature of the water bath was 35 C (95 F). undefined 6. At a stimulation frequency of 15 Hz how many stimuli were there per second? undefined Table 4: Measurement of Threshold Stimulus

Voltage (mV)

100 mV

200 mV

300 mV

400 mV

500 mV

Maximum Force (gf) (Motor unit 1)

Effect of Stimulation Value on Twitch Contraction Force 0 0.022 0.044 0.066 0.088 0.11 100 mV 200 mV 300 mV 400 mV 500 mV 1. What is the threshold stimulus? undefined 2. What is the maximum force generated at the threshold stimulus? undefined 3. How does increasing voltage above threshold stimulus affect force development? undefined Table 5: Muscle Length and Contraction Force

Maximum Force (gf) (Motor unit 1)

Muscle length (mm)

6.5

7.0

7.5

8.0

8.5

9.0

9.5

10.5

Effect of Muscle Fiber Length on Contraction Force 0.06 0.07 0.08 0.09 0.1 0.11 6 7 8 9 10 11 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 4. What was the average force of contraction at a muscle length of 7.0 mm? undefined 5. What was the optimal muscle length (muscle length that generated the maximum force)? undefined 6. What was the maximum force generated at optimal length? undefined 7. How does increasing muscle fiber length affect force of muscle contraction? undefined Table 6: Stimulation Frequency and Contraction Force

Stimuli per second

7.5

Maximum Force (gf) (Motor unit 1)

Effect of Stimulation Frequency on Contraction Force 0.1 0.15 0.2 0.25 0.3 0.35 10 20 30 40 50 60 7.5 15 30 45 60 8. What was the force of contraction at a stimulation frequency of 22.5? undefined 9. At what frequency of stimulation was the maximum force generated? undefined 10. What was the maximum force generated in this experiment? undefined 11. How does increasing stimulation frequency affect force production? undefined 1. Explain why muscle contraction does not occur below threshold stimulus. undefined 2. When stimulation voltage was increased above threshold, did the force of contraction increase, decrease, or stay the same? Explain why this occurred. undefined 3. Explain why force of contraction changes with muscle fiber length. undefined 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? undefined 5. Explain why differences in intracellular calcium levels result in differences in force production. undefined 6. In the experiment Effect of Stimulation Frequency on Contractile Force, why was muscle fiber length set to optimal length? undefined 7. Restate your predictions that were correct and give data from your experiment that support them. Restate your predictions that were not correct and correct them with supporting data from your experiment. undefined 1. Botulinum toxin is taken up by axon terminals and inhibits the ability of a motor neuron to stimulate a skeletal muscle motor unit to contract by preventing the release of acetylcholine from the axon terminal. Explain how this prevents skeletal muscle contraction. undefined 2. Explain why injecting Botox (derived from botulinum toxin) into a superficial facial muscle reduces the appearance of deep facial wrinkles called muscle lines. Hint: Superficial facial muscles are attached at one end to skin. undefined