[PhysioEX Chapter 2 exercise 1] PEX-02-01

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Exercise 2: Skeletal Muscle Physiology: Activity 1: The Muscle Twitch and the Latent Period Lab Report
Pre-lab Quiz Results
You scored 100% by answering 5 out of 5 questions correctly.

1. Skeletal muscles are connected to bones by
   You correctly answered: b. tendons.
2. Skeletal muscles are composed of hundreds to thousands of individual cells called
   You correctly answered: c. fibers.
3. The term motor unit refers to
   You correctly answered: 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
   You correctly answered: a. one contractile response to a single action potential.
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   Experiment Results
   Predict Question:
   Predict Question: Will changes to the stimulus voltage alter the duration of the latent period?
   Your answer : b. No, changing the stimulus voltage will not change the latent period duration.
   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?
   You correctly answered: c. the latent period
   What occurs during the latent period of these isometric contractions?
   You correctly answered: b. All the steps of excitation-contraction coupling occur.
   Experiment Data:
   Voltage Length Active Force Passive Force Total Force Latent Period
   0.0 75 0.00 0.00 0.00 ---
   3.0 75 1.04 0.00 1.04 ---
   4.0 75 1.32 0.00 1.32 3.20
   6.0 75 1.65 0.00 1.65 3.20
   8.0 75 1.81 0.00 1.81 3.20
   10.0 75 1.82 0.00 1.82 3.20

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 fiber : single muscle cell that consist skeletal muscle.
   motor unit : a motor neuron with the muscle fiber it innervates.
   skeletal muscle twitch : respond to a single action potential.
   electrical stimulus : it make the muscle contract.
   latent period : period between stimulating and start of constraction.
2. What is the role of acetylcholine in a skeletal muscle contraction?
   Your answer:
   it diffuses to the muscle fiber's membrane and binds to receptors in the motor endplate and make electric potential.
3. Describe the process of excitation-contraction coupling in skeletal muscle fibers.
   Your answer:
   the neutromusclular juction leads to the end platepotential and the end platepotential triggers a process resulting in the
   contraction of a muscle cell.
4. Describe the three phases of a skeletal muscle twitch.
   Your answer:
   latent period : between the generation of an action potential in a muscle cell and the start of the contraction.
   contraction : between end of the latent period and ends when the muscle tension peaks.
   relaxation : 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 experiment, the latent period remained the same as I predicted
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:
   The sodium ions move into the cell during the threshold stimulus to make the membrane depolarize.