Twitch Response And Recruitment - Summation And Tetanus

Questions: Twitch Response And Recruitment 1. Did you get a measurable twitch with a stimulus of 0 mA? What does this tell you about the number of muscle fibers contracting at this stimulus current?2. What was the smallest current required to produce a contraction (the threshold current)? What proportion of the fibers in the muscle do you think were contracting to produce this small response? 3. What was the smallest current required to produce the maximum (largest) contraction? What proportion of the fibers in the muscle do you think were contracting to produce this maximal response?4. What do you conclude happened to the number of fibers contracting as the current was raised from threshold to that required to produce a maximal contraction? 5. Why does varying the stimulus strength affect the twitch force? Summation And Tetanus 6. The stimulus interval has a profound effect on the contraction force of the muscle. In your own words explain what happened when the muscle was stimulated in rapid s uccession. What was the minimum time required for the subject's muscle twitches to add together (summation)?7. You use a short period electrical stimuli to observe muscle fibers contracting continuously (tetanus). Chemical agents can cause tetanus by interfering with the motor neurons. These agents include a toxin produced by the soil bacterium Clostridium tetani. One of the symptoms of these agents is called 'spastic paralysis'! Explain in your own words why these agents would be a bad thing for you and your muscles.Study Questions Fatigue is not well understood. Some factors that have been proposed to explain the fall in force during fatigue include: changes in the 'sense of effort', loss of 'central drive', failure of neuromuscular propagation, reduction in calcium release in excitation-contraction coupling, metabolic changes in the muscle, and reduction in muscle blood flow owing to compression of blood vessels. 8. Do your experiments help to decide which factors are important? 9. Almost all subjects will show a declining force (pseudo-fatigue), while their eyes are shut, that is very similar to fatigue. This is, however, not true fatigue, because the full 50% force can be exerted easily, as can be seen when the subject's eyes are opened again. What explanations can you think of for pseudo-fatigue? Answers: 1. No, there was no twitch response for 0mA. The force observed for the twitch response was at 3mA. Since, there was no force observed at 0mA stimulus, it shows that none of the muscle contracted. Thus it can be concluded that there is no response to Zero stimulus. 2. 3mA of stimulus current just produced a contraction i.e. 3mA is the threshold current. Though this is the threshold current but it doesn't produces the smallest contraction force. The smallest force is observed at 6mA. Very small proportion of fibers in the muscle participated in the contraction as very less force, of magnitude 0.004, was produced. 3. 16mA of stimulus current was seen to produce the largest contraction of magnitude 0.035. However, on increasing the current there was a downfall in the contraction force. Also, multiple values of contraction force was observed at same amount of stimulus current. A greater proportion of fibers in the muscles were contracting to produce this maximal response. 4. The fibers in the muscle didn't contract initially i.e. at 0mA. But as the current was raised and it reached up to the threshold current, small proportion of fibers contracted and a response was seen. Further when the current was increased a dip in force was observed till 6mA that shows lesser amount of fibers participated. Now on increase of current from this point a steady increase in the contraction force was observed and thus can be concluded that a greater number of fibers were contracting to produce a response (Hansson, 2012). Hence, we can conclude that on increasing the stimulus more number of fibers contracted. 5. Excitation of the fibers induces pain directly over the affected area and the pain spreads toward over a zone and local twitch response is seen. As the stimulus strength is increased the affected zone becomes larger and more number of fibers contract. This causes a variation in the twitch force and different forces are observed on different stimulus. 6. Table 1 shows the first and second response at different stimulus intervals. When the interval was 50ms, the response was undetectable. On increasing the interval to 100ms, the first response was difficult to trace but the second response was observed to be 0.012. First response was not observed until the interval was increased to 150ms. At this interval, first response was seen to be equal to 0.011. The second response was 0.017. On gradually increasing the intervals both first and second response were observed. When the muscles were stimulated in rapid succession, two points were noticed. First, on increasing the stimulus intervals the response force decreased i.e. for shorter intervals a larger force was observed and for larger intervals lesser value of force was observed. Second, for the same interval, value of second response was larger than the first. The minimum time required for the subject's muscle twitches to add together was 150ms. 7. Spastic paralysis is combination of paralysis, increasedtendon reflexactivity andhypertonia. It is commonly referred as tightness, stiffness or pull of muscles. Box-car shaped, bacterium Clostridium tetani is an anaerobicbacterium. It isGram-positive. A potent biological toxin is produced,tetanospasmin, which causestetanus. Some symptoms of this include painful muscular spasms that leads to respiratory failure and sometime causes death. Because of Clostridium tetani, unending spasms can start. Tetanospasmin discharged in the injury is consumed into the flow and achieves the finishes of engine neurons everywhere throughout the body. Focal sensory system is assaulted at a few locales, including nerve terminals, spinal string and the cerebrum and thoughtful sensory system (Connan, Denve, Mazuet Popoff, 2013). Fringe engine neuron terminals are reinforced and poison enters the nerve axons and it spreads crosswise over synaptic intersections to the nerve cell body in the mind stem and spinal string until it achieves the focal sensory system where it quickly ties to inhibitory engine nerve endings. With lessened restraint, the resting terminating rate of the alpha engine neuron increments and it accordingly delivers inflexibility, unopposed muscle withdrawal and fit. A few gimmicks are an unbending grin, lock-jaw and inflexible, curved back. Seizures may happen and the autonomic sensory system might likewise be influenced. Study Questions Fatigue is not well understood. Some factors that have been proposed to explain the fall in force during fatigue include: changes in the 'sense of effort', loss of 'central drive', failure of neuromuscular propagation, reduction in calcium release in excitation-contraction coupling, metabolic changes in the muscle, and reduction in muscle blood flow owing to compression of blood vessels. 8. Muscle fiber may go short of substrates causing fatigue. Release of calcium might get interfered or inability of calcium to stimulate muscle contraction arises because muscle fiber gets accumulated with metabolites. During exercise substrates depletes and results in lack of intracellular energy sources for contractions to take place. Deposition of Lactic acid causes acidity of muscles and thus it lowers the sensitivity of the muscles. 9. Prolongedexerciseleads to mental fatigue and it also impairs the function of central nervous system.Sleepinessandmentalfatigue are also seen due to build up of tryptophan. Individual muscle fibers respond to a stimulus with maximum force and sometime none at all (Marino, 2011). Muscle has to be relaxed once it gets contracted. Prolonged or repetitive contraction and relaxation of muscles causes fatigue and is familiar to anyone who is running and calf muscle feel cramps. With fatigue, there is a sense of weakness and even discomfort. The mechanism of fatigue is multifactorial and involves the central nervous system, peripheral nervous system, muscle units and individual muscle fibers. References Connan, C., Denve, C., Mazuet, C., Popoff, M. (2013). Regulation of toxin synthesis in Clostridium botulinum and Clostridium tetani.Toxicon,75, 90-100. doi:10.1016/j.toxicon.2013.06.001 Hansson, S. (2012). Maximal and perimaximal contraction.Synthese,190(16), 3325-3348. doi:10.1007/s11229-012-0167-y Ivarsson, N., Rundqvist, H., Lanner, J. (2012). Endurance Exercise Increases Force Production in Mouse Fast-Twitch Muscles.Biophysical Journal,102(3), 364a. doi:10.1016/j.bpj.2011.11.1988 Marino, F. (2011).Regulation of fatigue in exercise. Hauppauge, N.Y.: Nova Science Publishers. Pearson, D. (2004). Muscle Fibers.Strength And Conditioning Journal,26(1), 45. doi:10.1519/00126548-200402000-00013