Muscle Contraction Experiment

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The introduction of this lab report discussed and elaborated how muscle contraction is an intricate and precise step-by-step process in the body. The concepts outlined at the introduction intertwine with the experiments performed in this lab. The experiments aimed to showcase the physiological cause and effect of skeletal muscle responses towards various situations. For instance, the first experiment demonstrated spatial summation through the form of muscle recruitment. The cause of this reaction was due to the increased voltage input on the sciatic nerve. Furthermore, the second case study exhibited temporal summation, where constant stimulus exposure led to a fusion of twitches called a tetanic contraction. As for the third experiment, the …show more content…

Figure 1 shows a gradual upward trend that eventually plateaus as the experiment came to an end. The first two trials produced minor contractions that signified the activation of the small motor units, thus agreeing with Henneman’s Principle. However, the third trial had the largest single increase of tension, soaring from 57.65 grams of force to 86.72 grams. The physiological explanation tied to this sharp increase was due to the activation of large motor units, rather than small motor units. By this order, it was the complete opposite of the Henneman’s Principle. However, muscle contraction though specific in the process of excitation-contraction, is also adaptable to various situations due to their properties. The case in Figure 1 involved the electrical stimulus taking the path with the least resistance, and therefore was energetically favorable. By default, large motor neurons have greater diameter size compared to small motor neurons. This equates to a relationship where size determines the neuron’s resistance to electrical conduction. Meaning, the larger the diameter the lesser the resistance. Therefore, trial 3 was an indication of large motor units being recruited first before small motor units. Additionally, this assertion reflected the sharp increase in tension, since large motor units produce greater force of tension versus small motor units (Widmaier et al, 2015, …show more content…

The previous trial involved multiple sources of motor units contracting together to generate a strong tension. This time, fusion of contraction came from the frequency of stimulus input. In this case, the stimulus magnitude remained the same throughout the trial, while the frequency of parts per second increased in succession per 30 seconds. Going back to Figure 2, the graph revealed a sigmoidal trend, or an “s” shaped graph. The correlation existed between an increase in twitch tension and frequency of stimulus on the sciatic nerve. The physiology behind this paralleled relationship was due to the fusion of small muscle twitches with no relaxation period. This resulted in a sustained, and maximal contraction better known as a fused tetanus. It can be said that the frequency of action potential determines the level of tension increase, until the maximum tension is obtained (Widmaier et al, 2015,

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