EXERCISE 2: Skeletal Muscle Physiology
ACTIVITY 1: The Muscle Twitch and the Latent Period
1. The latent period of the skeletal muscle that was tested in this lab simulation was a. about 1 second.
b. less than 1 msec.
c. between 2-3 msec.
d. variable, depending on the voltage that was applied to it. C.
2. True or False: Another name for a muscle cell is “myofibril.” False
3. The largest active force that could be generated in the muscle is Activity 1 was _______ grams. 1.82
4. Define the terms skeletal muscle fiber, motor unit, skeletal muscle twitch, electrical stimulus, and latent period. Skeletal muscle fiber- usually attached to the skeleton, helps humans make voluntary decisions to walk, talk and sit up. Motor Unit- consists of a motor neuron and all of the muscle fibers it innervates/supplies. Skeletal muscle twitch- a brief contraction of all the muscle fibers in a motor unit in response to a single action potential in its motor neuron. A twitch has three phases. Latent, contraction, and relaxation phase Electrical stimulus- used to control muscle contractions
Latent period- the period of time that elapses between the generation of an action potential in a muscle cell and the start of a muscle contraction
5. What is the role of acetylcholine (ACh) in a skeletal muscle contraction? Acetylcholine diffuses into the muscle fiber’s plasma membrane and binds to receptors in the motor end plate starting a change in ion permeability that results in a graded depolarization of the muscle plasma membrane. 6. Describe the process of excitation-contraction coupling in skeletal muscle fibers. A shock is sent to thru the muscle, leading into the contraction of the of the muscle 7. Describe the three phases of a skeletal muscle twitch.
Latent period – the period of time that elapses between the generation of an action potential in a muscle cell and the start of a muscle contraction. Contraction phase – the period of time that starts at the end of the latent period and ends when muscle tension peaks. Relaxation phase – the period of time from peak tension until the end of the muscle contraction 8. Does the duration of the latent period change with different stimulus voltages? No
9. At the threshold stimulus, do sodium ions start to move into or out of the cell to bring about the membrane depolarization? Move Into
ACTIVITY 2: The Effect of Stimulus Voltage on Skeletal Muscle Contraction 10. The threshold voltage for the muscle in this lab simulation was ________ volts. When that voltage was used to stimulate the muscle, ________ grams of active force were generated. .8 volts and .02 grams
11. True or False: In a resting skeletal muscle cell, most of the calcium ions freely move through the cytoplasm of the cell.
12. 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? When increasing the voltage on isolated skeletal muscle, the active force was increased every time the voltage was increased until it reached a point that the force could not go any higher. 13. How is this change in whole-muscle force achieved in vivo (eg. in the human body)? The recruitment of additional motor units increases the total muscle force produced. 14. What happened in the isolated skeletal muscle when the maximal voltage was applied? Maximal tension in the whole muscle occurs when you reach maximal voltage. ACTIVITY 3: The Effect of Stimulus Frequency on Skeletal Muscle Contraction 15. True or False: There is no limit to the amount of force that a skeletal muscle can generate if it is stimulated by a high enough voltage at a very high frequency. False
16. The chemical ion or molecule that is primarily responsible for initiating the contraction of a muscle fiber is a. Na+
17. What is...
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