What kind of stimulus (electrical or chemical) travels from the terminal to the

Question

What kind of stimulus (electrical or chemical) travels from the terminal to the sarcolemma? Give the name and duration of each of the three phases of the muscle twitch, and describe what is happening during each phase. a., msec. b., msec, c., msec. Use the items in the key to identify the conditions described. Key: a. maximal stimulus b. multiple motor unit summation c. sub threshold stimulus d. tetanus e. threshold stimulus f. wave summation sustained contraction without any evidence of relaxation stimulus that results in no perceptible contraction stimulus at which the muscle first contracts perceptibly increasingly stronger contractions owing to stimulation at a rapid rate increasingly stronger contractions owing to increased stimulus strength weakest stimulus at which all muscle cells in the muscle are contracting

Explanation / Answer

5. The excitable tissues are the tissues that can produce electrical signals when they are excited. Nerve tissue and muscle tissue are the excitable tissues. The neurons or nerve cells receive the electrical signals, process and transmit the messages. The muscle cells receive the electrical signals and initiate the contractions. The stimulus travelling from axon terminal to sarcolemma is electrical signal.

6. The muscle contraction is accomplished in three phases called latent period, contraction and relaxation phases. Latent period is the phase 1 of muscle twitch. It lasts for about 2 to 3 msecs. In the latent period, action potential is moved across sarcolemma, down T-tubules to sarcoplasmic reticulu and releases the calcium ions. No tension is observed in this phase. Contraction is the second phase of muscle twitch. It lasts for long duration than latent period. During contraction, binding of actin/myosin and powerstrokes are observed with increased tension. The relaxation phase is third phase of muscle twitch and lasts for long duration than contraction phase. In this phase, the myosin is gets detached decreasing the tension in the muscle.

7.

1. Sustained contraction without evidence of rtelaxation is called tetanus. It is rapid and the contraction is for very long duration. (1) matches with option (d).

2. Stimulus with no perceptible contraction is known as subthreshold stimulus. (2) matches with option (c).

3. Muscle contraction is observed first perceptibly in threshold stimulus. (3) matches with option (e).

4. Wave or temporal summattion results in increasingly stronger contractions owing to stimulation at a rapid rate. (4) matches with option (f).

5. Increasingly stronger contractions owing to increased stimulus strength is resulted in multiple motor unit contraction. (5) matches with option (b).

6. Maximal stimulus is the weakest stimulus at which all muscle cells in the muscle are contracting. (6) matches with option (a).

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