Part 2 Summation, Tetanus, Fatigue Stimulus frequency at which summation is firs
ID: 3513401 • Letter: P
Question
Part 2 Summation, Tetanus, Fatigue Stimulus frequency at which summation is first apparent stimulus every 0 msec 11z which is equal to one Hz whichis equai toe Stimulus frequency at which complete tetanus first apparent6 stimulus every 6 msec 6 l 0.28 Time to fatigue (delta T from beginning ofcomplete tetanus to a 50% drop in force) 5-8-2.45 3. What is the physiological basis for summation? i.e. What is occurring to yield higher force generation as stimulus frequency is increased? 4. Define tetanus. 5. Name three physiological parameters that can contribute to muscle fatigue.Explanation / Answer
3. Wave Summation occurs when one more than one stimulus administered close in time. As a result, the relaxation of the preceding stimulus overlaps with the stimulus of the next contraction. Hence, the relaxation phase of the muscle twitch becomes shorter. This causes the contractions to become more powerful. When the stimulus frequency was increased (as voltage increased), the contraction of first stimulus starts merging with the contraction of the next and so on. As a result, the relaxation starts to decrease with increasing voltage. Due to wave summation as frequency went on increasing, the force will increase due to less and lesser relaxation phases. The strength of the contraction depends on frequency of stimulation. Presence of calcium ions is responsible for the decrease in relaxation of the muscle.
4. Tetanus is the state when there is no relaxation of the muscle. When the strength is at a maximum rate, the myocytes will remain in a persistent contracted state, which is known as tetanus. A limit exists to the maximum capacity of the muscle to contract as there is physical limitation of the actin-myosin cross bridging. At above the tetanizing frequency, no further muscle stimulation will occur. At tetanus, the muscle is responding to stimulus at a high rate. When muscle is stimulated at high frequency, the calcium ions in sarcoplasm increases. When the levels of calcium in sarcoplasmic reticulum reach its maximum level, it results in tetanus tension, allowing no relaxation of the muscle.
5. Fatigue is the decline in the ability of the muscle to respond to repeated stimulus. Frequency of the impulse affects muscle fatigue.
Several factors contribute to muscle fatigue:
1) Oxygen depletion and Lactic acid accumulation: As muscle is contracting faster, the amount of ATP required is higher. Hence, the muscle utilizes anaerobic breakdown of glucose as amount of oxygen supply to the muscle is far less than what is required. The breakdown of glucose for anaerobic respiration (due to less oxygen supply) will lead to accumulation of lactic acid. This will cause damage to muscle fibers and result in fatigue.
2) Calcium and ATP: The myocytes can less responsive with prolonged stimulation by either decrease in Ca++ availability or decrease in ATP. However, calcium depletion has less severe effect that ATP depletion.
3) CreatinePhosphate: Creatine phosphate is broken down to provide inorganic phosphate during muscle contraction. The amount of inorganic phosphates increase which results in muscle fatigue.