Name: Courtney.Sims 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.
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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 : c. The active force will first increase and then plateau at some maximal value as the stimulus voltage increases. 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 6. Enter the threshold voltage for this experiment in the field below and then click Submit Data to record your answer in the lab report You answered: .8 volts 12. Enter the maximal voltage for this experiment in the field below and then click Submit Data to record your answer in the lab report. You answered: 10 volts Experiment Data: Voltage 0.0 0.2 0.8 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0
Post-lab Quiz Results You scored 100% by answering 6 out of 6 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). 6. A sufficiently strong electrical stimulus applied to an isolated, mounted skeletal muscle induces the development of muscle force, or muscle tension. Which of the following statements concerning this observation is true? You correctly answered: c. The electrical stimulus mimics acetylcholine release at a neuromuscular junction
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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: As the stimulus voltage is increased past the muscle’s threshold voltage, the amount of force in the entire muscle increases. Each time the voltage was increased the force generated from the muscle also increased. This occurs because as the voltage increases, and is delivered to the whole muscle, more fibers are activated and causes total force produced by the muscles to increase.
2. How is this change in whole-muscle force achieved in vivo? Your answer: The increase of electrical current causes a progressive increase in the amount of muscle force based on the amount of the electrical current. At the beginning stage, the electric current must surpass the threshold voltage. Once the stimulus voltage goes beyond the threshold it creates whole muscle force. Increasingly the force gets stronger with the higher stimulus voltage until it plateaus at Maximal tension. The Maximal tension has a maximum amount of voltage that it will achieve to increase the force, but only to a maximum point. Whole-Muscle Force is achieved in Vivo by recruitment of additional motor units that increase the total muscle force produced.
3. What happened in the isolated skeletal muscle when the maximal voltage was applied? Your answer: All of the muscle fibers in the isolated skeletal muscle became depolarized and all developed active force. So each of the fibers were involved in the active force generated from the maximal voltage.
