Exercise 2 Skeletal Muscle Physiology

PhysioEx Lab Report Exercise 2: Skeletal Muscle Physiology Activity 2: The Effect of Stimulus Voltage on Skeletal Muscle Contraction Name: Date: 15 September 2020 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: motor neurons. 2 A single action potential propagating down a motor axon results in You correctly answered: 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: the sarcoplasmic reticulum. 4 During the latent period for an isometric contraction You correctly answered: the cellular events involved in excitation-contraction coupling occur. Experiment Results Predict Question 1 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: The active force will continually increase. Stop & Think Questions 1 What do you observe in the active force display when the stimulus voltage is set to 0.0, and why does this observation make sense? You correctly answered: 0.00; 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: threshold voltage. 3 Enter the threshold voltage for this experiment. You answered: 0.8 volts. 4 Enter the maximal voltage for this experiment. You answered: 8.5 volts. Experiment Data Voltage (v) Length (mm) 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 Voltage = 0.0 V Voltage = 0.2 V Voltage = 0.8 V Voltage = 1.0 V y y Voltage = 1.5 V Voltage = 2.0 V Voltage = 2.5 V Voltage = 3.0 V Voltage = 3.5 V Voltage = 4.0 V Voltage = 4.5 V Voltage = 5.0 V Voltage = 5.5 V Voltage = 6.0 V Voltage = 6.5 V Voltage = 7.0 V Voltage = 7.5 V Voltage = 8.0 V Voltage = 8.5 V Voltage = 9.0 V Voltage = 9.5 V Voltage = 10.0 V Post-lab Quiz Results You scored 100% by answering 6 out of 6 questions correctly. 1 Motor unit recruitment refers to You correctly answered: 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: 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: threshold voltage. 4 By definition, the is the amount of stimulus required to successfully recruit muscle fibers into developing active force. You correctly answered: maximal voltage. 5 Why was a maximal voltage observed in this experiment? You correctly answered: 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: The electrical stimulus mimics acetylcholine release at a neuromuscular junction. 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: The total force of the muscle increases when the stimulus voltage is increased. My predictions were accurate in that the force will continually increase, but I was wrong in failing to realize it would only be a certain point. The active force plateu'd at 8.5 volts. 2 How is this change in whole-muscle force achieved in vivo ? Your answer: The whole-muscle force is achieved in vivo because because additional motor units were used as an increase to the force produced by the total muscle. 3 What happened in the isolated skeletal muscle when the maximal voltage was applied? Your answer: The fibers in the isolated skeletal muscles were depolarized, and an active force was created. Maximal voltage was applied when all of the fibers in the skeletal muscle participated. all the