Phyisoex 9.0 Reveiw 2

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Activity 1 – The Muscle Twitch and Latent
1)Define the terms skeletal muscle fiber, motor unit, skeletal muscle twitch, electrical stimulus, and latent period. Skeletal Muscle Fiber: Skeletal muscle cells that are composed of hundreds to thousands of individual cells that produce muscle tension. These fibers are what move our bodies and generate muscle tension/force that enables us to have manual dexterity. Motor unit: consists of one motor neuron and all of the skeletal muscle fibers that it stimulates. The unit is located at the neuromusclular junction, where the axon terminal of the neuron meets, also called the motor end plate. Skeletal Muscle Twitch: A period of excitation-contraction in which electrical pulses trigger action potentials, The twitch is the result of a mechanical response to a single action potential. Electrical Stimulus: An isolated stimulus that sends energy through a muscle in which a response occurs. The stimulus generates movement in the muscle and causes the muscle to generate contractions. Latent Period: The beginning stage of muscle contractions. This stage produces no muscle force, but prepares the cells for oncoming contractions by releasing chemicals to the cells.

2)What is the role of acetylcholine (ACh) in a skeletal muscle contraction? ACH is released at the end-plate potential. ACH diffuses into the sarcolemma, attaches to the receptors in the motor end plate and causes a change in the ions permeability that creates graded depolarization of the end-plate potential. Basically, it attaches to the receptors in the motor-end plate and creates the beginning process of triggering muscle contractions.

3)Describe the process of excitation-contraction coupling in skeletal muscle fibers. The motor unit meets at the neuromusclular junction, where the axon terminal of a neuron and muscle fiber's plasma membrane meet, also called the motor end plate. What occurs in this area lead to the end-plate potential, where an action potential in motor neurons causes the release of ACH. The ACH diffuses into the muscle fiber membrane and changes the ions permeability that creates graded depolarization of the end-plate potential. The end-plate potential triggers events that create contraction of the muscle cell. This entire process of events makes up what is known as excitation-contraction coupling in the skeletal muscle fibers.

4)Describe the three phases of a skeletal muscle twitch. Latent Phase: During this phase there is no muscle contraction. This phase is the period of time prior to muscle contractions. The latent phase, chemical changes in the cells occur in preparation for muscle contractions. Contraction Phase: Is the period in which the muscle tension is at it's highest. This is the time where the greatest amount of muscle force is generated. It begins at the end of the latent period and ends when tension peaks at it's highest. Relaxation Phase: The period of contraction after the contraction phase, and ends at end of muscle contraction.

5)Does the duration of the latent period change with different stimulus voltages? No. In all tests, the latent period remained the same.

6)At the threshold stimulus, do sodium ions start to move into or out of the cell to bring about the membrane depolarization? The threshold is the time at which the sodium ions start moving into the cell to bring about the membrane depolarization.

ACTIVITY 2: The Effect of Stimulus Voltage on Skeletal Muscle Contraction

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? 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...
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