Skeletal Muscle Physiology

The Muscle Twitch and the Latent Period Lab Report Pre-lab Quiz Results You scored 20% by answering 1 out of 5 questions correctly. 1. Skeletal muscles are connected to bones by Your answer : c. ligaments. Correct answer: b. tendons. 2. Skeletal muscles are composed of hundreds to thousands of individual cells called Your answer : b. myofibrils. Correct answer: c. fibers.

3. The term motor unit refers to Your answer : b. all of the activated muscle fibers within one skeletal muscle. Correct answer: c. one motor neuron and all of the skeletal muscle fibers it innervates.

4. The motor neuron and muscle fiber intersect at what is called You correctly answered: d. the neuromuscular junction. 5. A twitch is Your answer : c. multiple contractile responses to a series of action potentials. Correct answer: a. one contractile response to a single action potential.

Experiment Results Predict Question: Predict Question: Will changes to the stimulus voltage alter the duration of the latent period? Your answer : a. Yes, changing the stimulus voltage will change the latent period duration proportionately.

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Stop & Think Questions: What is the period of time that elapses between the generation of an action potential and the start of muscle tension development in a muscle fiber?

Your answer : d. the recess period Correct answer: c. the latent period What occurs during the latent period of these isometric contractions? Your answer : a. The length of the muscle fiber is sliding into an optimal length. Correct answer: b. All the steps of excitation-contraction coupling occur. Experiment Data: Voltage 0.0 3.0 4.0 6.0 8.0 10.0 Length 75 75 75 75 75 75 Active Force 0.00 1.04 1.32 1.65 1.81 1.82 Passive Force 0.

00 0.00 0.00 0.00 0.00 0.00 Total Force 0.00 1.04 1.32 1.65 1.81 1.82 Latent Period

Post-lab Quiz Results You scored 100% by answering 7 out of 7 questions correctly. 1. An action potential in a motor neuron triggers the release of which neurotransmitter? You correctly answered: b. acetylcholine 2. The term skeletal muscle fiber refers to You correctly answered: a. an individual skeletal muscle cell. 3. The graded depolarization in the skeletal muscle fiber that is elicited in response to one action potential from the motor neuron is called You correctly answered: c. an EPP (end-plate potential).

4. Which of the following is not a phase of a skeletal muscle twitch? You correctly answered: b. hyperpolarization phase 5. A skeletal muscle twitch is You correctly answered: a. one contractile response to a single action potential. 6. Which of the following correctly matches the twitch phase with its definition? You correctly answered: d. the contraction phase: the time between the end of the latent period and peak muscle tension 7. 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

Review Sheet Results 1. Define the terms skeletal muscle fiber, motor unit, skeletal muscle twitch, electrical stimulus, and latent period. Your answer: Skeletal muscle fibers are usually attached to the skeleton and make voluntary actions such as walking, talking and standing up possible. A motor unit consists of a motor neuron and all of the muscle fibers it innervates. Skeletal Muscle twitch is the mechanical response to a single action potential. It has three phases known as the latent, contraction, and relaxation phase. Electrical stimulus is used to control muscle contractions. Latent Period is the period of time that elapses between the generation of an action potential in a muscle cell and the start of muscle contraction.

2. What is the role of acetylcholine in a skeletal muscle contraction? Your answer: Acetylcholine diffuses onto the muscle fiber's plasma membrane and binds to receptors in the motor end plate initiating a change in ion permeability that results in a depolarization of the muscle plasma membrane. 3. Describe the process of excitation-contraction coupling in skeletal muscle fibers. Your answer: The events that occur at the neuromuscular junction lead to the end plate potential. The end plate potential triggers a series of events that results in the contraction of a muscle cell. The entire process is called the excitation contraction coupling.

4. Describe the three phases of a skeletal muscle twitch. Your answer: The latent phase is the period of time between the action potential in a muscle cell and the start of muscle contraction. The Concentration phase starts at the end of the latent period and ends when the muscle tension peaks. The relaxation phase is the period from peak tension until the end of the muscle contraction.

5. Does the duration of the latent period change with different stimulus voltages? How well did the results compare with your prediction? Your answer: In all of the tests the latent period remained the same. The results proved that I was incorrect in my hypothesis. 6. At the threshold stimulus, do sodium ions start to move into or out of the cell to bring about the membrane depolarization? Your answer: During the threshold stimulus sodium ions move into the cell.