[PhysioEX Chapter 2 exercise 2] PEX-02-02

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Exercise 2: Skeletal Muscle Physiology: Activity 2: The Effect of Stimulus Voltage on Skeletal Muscle Contraction Lab
Report
Pre-lab Quiz Results
You scored 100% by answering 4 out of 4 questions correctly.

1. Skeletal muscle fibers are innervated (stimulated) by
   You correctly answered: c. motor neurons.
2. A single action potential propagating down a motor axon results in
   You correctly answered: d. a single action potential and a single contractile event in the muscle fibers it innervates.
3. In resting skeletal muscle, calcium is stored in
   You correctly answered: c. the sarcoplasmic reticulum.
4. During the latent period for an isometric contraction
   You correctly answered: c. the cellular events involved in excitation-contraction coupling occur.

Experiment Results
Predict Question:
Predict Question: As the stimulus voltage is increased from 1.0 volt up to 10 volts, what will happen to the amount of active
force generated with each stimulus?
Your answer : a. The active force will continually increase.
Stop & Think Questions:
What do you see in the active force display when the stimulus voltage is set to 0.0, and why does this observation make
sense?
You correctly answered: a. 0.00 g; there was no activation of skeletal muscle fibers by this stimulus.
What is the lowest stimulus voltage that induces active force in the skeletal muscle?
You correctly answered: b. threshold voltage

1. Enter the threshold voltage for this experiment in the field below and then click Submit to record your answer in the lab
   report
   You answered: 0.8 volts
2. Enter the maximal voltage for this experiment in the field below and then click Submit to record your answer in the lab
   report.
   You answered: 8.5 volts
   Experiment Data:
   Voltage Length Active Force Passive Force Total Force
   0.0 75 0.00 0.00 0.00
   0.2 75 0.00 0.00 0.00
   0.8 75 0.02 0.00 0.02
   1.0 75 0.15 0.00 0.15
   1.5 75 0.43 0.00 0.43
   2.0 75 0.66 0.00 0.66
   2.5 75 0.87 0.00 0.87
   3.0 75 1.04 0.00 1.04
   3.5 75 1.19 0.00 1.19
   4.0 75 1.32 0.00 1.32
   4.5 75 1.42 0.00 1.42
   5.0 75 1.51 0.00 1.51
   5.5 75 1.59 0.00 1.59
   6.0 75 1.65 0.00 1.65
   6.5 75 1.70 0.00 1.70
   7.0 75 1.74 0.00 1.74
   7.5 75 1.78 0.00 1.78
   8.0 75 1.81 0.00 1.81
   8.5 75 1.82 0.00 1.82
   9.0 75 1.82 0.00 1.82
   9.5 75 1.82 0.00 1.82
   10.0 75 1.82 0.00 1.82

Post-lab Quiz Results
You scored 100% by answering 5 out of 5 questions correctly.

1. Motor unit recruitment refers to
   You correctly answered: a. an increase in the number of active muscle fibers to increase the force developed in a muscle.
2. Active tension (or force) in a skeletal muscle fiber results from
   You correctly answered: a. activation of cross bridge cycling via increased intracellular calcium levels.
3. The ________ is the minimal stimulus needed to cause a depolarization of the muscle plasma membrane (sarcolemma).
   You correctly answered: d. threshold voltage
4. By definition, the ________ is the amount of stimulus required to successfully recruit all the muscle fibers into
   developing active force.
   You correctly answered: c. maximal voltage
5. Why was a maximal voltage observed in this experiment?
   You correctly answered: b. At the maximal voltage, all the muscle fibers contained in this muscle are depolarized and they
   all develop active force (that is, they were all successfully recruited).

Review Sheet Results

1. Describe the effect of increasing stimulus voltage on isolated skeletal muscle. Specifically, what happened to the muscle
   force generated with stronger electrical stimulations and why did this change occur? How well did the results compare with
   your prediction?
   Your answer:
   increasing the stimulus voltage on the skeletal muscle makes the situration that the total force produced by the muscle
   increases. as I predicted, the active force increased continually but when maximum volt reched, it did not increased.
2. How is this change in whole-muscle force achieved in vivo?
   Your answer:
   the change in the whole-muscle force was achieved in vivo where additional motor units are recruited to increase the total
   muscle force produced basically. at the beginning, the electric current must go beyond the threshold. once the stimulus
   voltage goes over the threshold, it creates whole muscle force. increasingly the force gets stronger with the higher
   stimulusvoltage until it reach at maximum..
3. What happened in the isolated skeletal muscle when the maximal voltage was applied?
   Your answer:
   all of the muscle fibers in the skeletal muscle became depolarized and all makes active force. all of the fiber participated to
   make maximal voltage.