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Bio 273 Lab report 1

Bio 273 Lab report 1 - Experiment 3 Characteristics of the...

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Experiment # 3 Characteristics of the contraction of skeletal muscle. Introduction: The purpose of this lab was to explore some of the functional properties of the skeletal muscle using stimulus-response experiments. The hind leg of a migratory locust was used to determine values for the threshold stimulus voltage, and illustrate the various properties of the skeletal muscle as well. In this experiment, the muscle was stimulated to find the threshold stimulus, after which a single contraction was used to examine a simple twitch. The force exerted by a twitch is
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determined by the number of motor units responding at the same time. Increasing the stimulation voltage of the muscle increases the number of motor units contracting at the same time, thus producing a stronger twitch. There are three different periods in a single twitch, which are: latency period, contraction period and relaxation period. The latency period is the interval between the stimulus and the muscle contraction, and it usually takes about 5 milliseconds to occur. The contraction period is when the muscle shortens and does its work, and lasts usually 40 milliseconds. Relaxation period is when the muscle elongates and returns to its original position, and usually lasts 50 milliseconds. (Silverthorn, 2010) When the repeated action potentials are separated by long intervals of time, the muscle fiver has time to relax completely between the stimuli. However, if the stimulus time between the two action potentials is shortened, the muscle does not have time to relax in between contractions. Therefore, a more forceful contraction is generated because the two contractions are summed up together, and this is referred to as temporal summation. As the frequency of stimulation increases, a contraction if finally attained whose amplitude is greater than that of any single contraction. (Silverthorn, 2010) When the contractions occur at a high frequency, they are repeated within very short intervals, and eventually, the relaxation between the contractions completely diminishes and the muscle fibre achieves a state of maximal contraction, which is known as tetanus. If there is slight relaxation of the muscle fibres in between contractions, then it is called incomplete of unfused tetanus. If the stimulation rate is fast enough the muscle fibres have no time to relax, it is called fused or complete tetanus. (Silverthorn, 2010)
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