The right answer is A.
The sarcolemma is the plasma membrane of the striated muscle fibers, ensuring the diffusion of nerve impulses to the entire fiber, invaginating in places to form the transverse tubules surrounded by cisterns of the sarcoplasmic reticulum.
So, if the sarcolemma is altered, there will be a poor transmission of nerve impulses.
Increasing the frequency of muscle stimulation causes wave summation to occur, which causes an overlap of muscle twitch. When this muscle summation happens, the force generated in the muscle increases. This means that stimulating the muscle every 0.5 seconds will generate less muscle contraction force than when stimulated every 0.05 seconds
a. muscle contraction of sustained force resulting from repeated action potentials.
Tetanus is a symptom consisting of the constant contraction of one or more muscles. This can be caused by diseases or other physiological conditions that cause an increase in the frequency of action potentials that promote muscle contractions. Thus, the contractions overlap each other and consequently the muscle remains in a condition of constant contraction.
Figure E is the correct representation of the first part of the motion. When in a hanging position from the chin-up bar, the bicep muscles are stretched beyond their normal length already. So at this point they are at the peak of their capacity and you are at rest (this corresponds to the velocity v = 0 at t = 0). On contracting the bicep muscles and pulling your whole body up, you begin to gain speed and v increases. This increase in velocity is exponential. Soon the bicep muscles contract up to 80% their normal length reducing the force they can produce to keep you rising up to zero. The velocity change happens because the body is accelerating and the muscles can still supply a net force to lift you up. The acceleration is present because of this net force. The moment this force reduces to zero, the acceleration too reduces to zero. (From Newton's second law of motion). This reduction in acceleration is responsible for the reduction of the curvature of the v curve in figure E above. The point where the velocity becomes horizontal corresponds to the point where the muscles reach their maximum contraction unit and can supply no more net force and as a result no acceleration. This further results inba constant velocity which is the flat nature of the curve seen in diagram E.
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