MUSCLE TWITCH,TETANY,MUSCLE FATIGUE, RIGOR MORTIS.pptx

This section briefly covers muscle physiology. A muscle twitch has three phases: latent, contraction, and relaxation. Tetany includes incomplete and complete sustained contractions. Summation occurs when twitches combine due to rapid stimuli. Muscle fatigue results from prolonged use and energy depletion. Rigor mortis is post-death stiffness caused by ATP loss, locking muscles in contraction.

1. MUSCLE TWITCH, TETANY, MUSCLE FATIGUE, RIGOR MORTIS

2. MUSCLE TWITCH   The sum total of the muscular events, occurring during a single contraction,  is called muscle twitch (in human skeletal muscle it lasts for about .05 seconds). It is completed three stages, namely latent phase, contraction phase and relaxation phase.  1. Latent phase is   the time interval between the initial stimulation and the beginning of actual contraction. During this period, no physical changes occur, and the length and tension of the muscle remain the same. But, several biochemical changes take place. Transmission of the action potential to the sarcoplasmic reticulum and the release of Ca++ from sarcoplasmic reticulum to sarcoplasm occur during the latent phase.

3. 2.During the contraction phase, the muscle shortens and its tension increases . During the relaxation phase, the muscle returns to its original physical state and physiological condition. 3. Relaxation phase usually lasts longer than the contraction phase. The very short period, following a twitch, is known as refractory period. During this, the muscle will not usually respond to a second stimulus.  But, in skeletal muscles this period is so short(.002 second)that the muscle can respond to a second stimulus, even while contracting in response to the first one. The apparatus which can measure and graphically record the effects of a twitch contraction is known as myograph . The record or tracing produced by the myograph is called myogram .

4. TETANY Muscles do not normally contract in single twitches. They always contract in rapidly repeating twitches, in response to rapid relays of continuous impulses reaching them in quick succession. Sustained hyper contraction of muscles due to the fusion of numerous twitches with no time for relaxation between stimuli is known as tetanus or tetanic contraction In tetanic contraction, stimulations occur so rapidly (several hundred per second) that relaxation cannot occur in between two successive twitches. So, continuous stimuli result in the overlapping or fusion of successive twitches to form a large single twitch, which would last for a longer period, without further increase in strength.  Tetanus usually results from the depletion of ATP or other high-energy phosphates. 

5. There are two types of tetanic contraction, namely  Incomplete or unfused tetanus - stimuli are spaced so that the muscle can relax partially or incompletely in between successive stimuli. Complete or fused tetanus -  stimuli are fused so that relaxation is altogether absent in between successive stimuli.  The tension developed in tetanic contraction may be several times greater than that of a single twitch. In fact, tetanic contraction is the maximum possible response of a muscle and  so it represents the condition in which the maximal active state of the muscle is maintained by continuous stimulation

6. Summation of Twitches or Contractions In Tetanic contraction the refractory. Is considerably short or practically absent. So the muscle responds to a second stimulus even when it is contracting in response to the first one. As a result, the second contraction always superpositions or overlaps the first one such as  superpositioning  of one contraction over the previous one is known as temporal summation of twitches. It results in an excessive contraction or extreme shortening of the muscle much greater than that in a single stimulus or single twitch also the tension developed during summation would be much greater than that of a single twitch If two stimuli are too close together the second one will have no effect this is because the muscle membrane will be in the refractory. And it will not be able to elicit ah contraction triggering action potential

7. MUSCLE FATIGUE Muscle fatigue is the condition in which a muscle loses its powers for contraction, fails to respond to stimuli, and becomes relaxed and flabby.  This happens when a muscle has contracted many time in quick succession.  Cardiac muscles are immune to fatigue so that they can go on continuously contracting and relaxing till death.  In a fatigued skeletal muscle, the store of ATP, phosphocreatine and glycogen becomes almost exhausted, release of Ca++ from SR to sarcoplasm is very slow and much reduced, and there is considerable accumulation of lactic acid and other wastes.  Fatigue is primarily induced by lactic acid accumulation, even though it may be felt before the muscle reaches the exhausted state. The reason is that the neuromuscular junction gets fatigued before the muscle is fatigued.

8. RIGOR MORTIS Rigor mortis is a temporary condition in which all the muscles of a dead individual become rigid, non-elastic and permanently contracted. So, the body becomes stiff.  Rigor is a state of muscular rigidity due to the depletion of ATP, creatine phosphate, etc. Rigor mortis is the rigor after death.  Sometime after death, the enzymes stop functioning. At the same time, the ATP molecules become completely used up. Since enzymes are not functioning, ATP synthesis becomes impossible. So, energy is not available for the relaxation of muscle fibres , and they remain in the contracted state. After some time, the muscles undergo decomposition.  Rigor mortis commences nearly 3 hours after death, reaches maximum stiffness after 12 hours, and then gradually disappears.

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