Human Physiology Human Muscle Stimulus Response

Questions: 1. Above a certain stimulus current, the amplitude of the finger twitch no longer increases. Why does this happen? 2. Show your table with the average amplitudes of the finger twitches at each frequency. Answers: (1). Twitching is a contraction of the muscle of the finger that occurs in response to a rapid, single stimulus that excites a single isolated action potential in a muscle fiber (Volz et al.). However, for generating coordinated and controlled movements which are required for maintaining the homeostasis; isolated, single twitches are not sufficient. Excitation of many motor neurons is required for the generating movements in the body. Excitation of neurons occurs when an action potential reaches a threshold level. When the action potential reaches the threshold level, the Ca2+ gates open and an electric impulse is generated due to the electrochemical gradient (Adler). Action potentials work in a none or all manner. Due to this nature of action potential, the strength of a stimulus should have a minimum value to reach a threshold to excite an action potential in the muscle fiber (Adler). To achieve contraction of the muscle strength of stimulus must overcome a minimum threshold of an action potential. Once the threshold action potential is reached, the strength of the stimulus will not have any effect on the further increase of action potential. The increase in the strength of the stimulus will not increase the muscle contraction because the Ca2+ gates of the sacroplasmic reticulum remain open only for a short amount of time after opening; hence, there will be no effect on the action potential (Adler). For an organ to move, many motor neurons are involved in the contraction of the muscle. Minimum stimuli strength is required for contracting the muscle (Volz et al.).. A minimum strength of stimulus is necessary to reach the lowest threshold level. As the strength of the stimulus increases, more and more motor neurons will get excited and after a certain level of stimuli strength, there will be no change in the tension created by the muscle fibers as all the fibers are already excited, and the muscle is in contraction (Volz et al.). (2). Following is the table showing the average amplitudes of the finger twitches at different frequencies. V1 and V2 represent the amplitudes. 1 2 3 Averages Remarks Frequency (Hz) V2-V1 V2-V1 V2-V1 V2-V1 1 748.5 706.2 768.3 741 2 384.5 310.5 379.4 358.13 3 343.6 323.3 350.6 339.17 4 244.1 265.2 230.6 246.63 5 168.6 186.4 190.2 181.73 10 32.2 31.3 23.3 28.933 No relaxation time 15 2 3 2 2.3333 No relaxation due to Increase in frequency 20 0 0 0 0 Tetanu References: Adler, Elizabeth M. "Of muscle modulation and the CFTR gate."The Journal of general physiology145.4 (2015): 255-255. Volz, Lukas J., et al. "What makes the muscle twitch: motor system connectivity and TMS-induced activity."Cerebral cortex(2014): bhu032.