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Explain mechanism of muscle contraction

Answer» Mechanism of muscle contraction :\tMechanism of muscle contraction is explained by sliding filament theory which states that contraction of a muscle fibre takes place by the sliding of the thin filaments over the thick filaments.\tMuscle contraction is initiated by a signal sent by the central nervous system via a motor neuron.\tA motor neuron along with the muscle fibres connected to it constitutes a motor unit.\tThe junction between a motor neuron and the sarcolemma of the muscle fibre is called neuromuscularjunction or motor-end plate.\tNeurotransmitter releases here which generates an action potential in sarcolemma.\tThese causes release of Ca++ into sarcoplasm.\xa0\tThese Ca++ binds with troponin, thereby remove masking of active site.\tMyosin head binds to exposed active site on actin to form a cross bridge, utilizing energy from ATP hydrolysis.\tThis pulls the actin filament towards the centre of ‘A’ band.\t‘Z’ lines also pulled inward thereby causing a shortening of sarcomere i.e. contraction.\t‘I’ band get reduced, whereas the ‘A’ band retain the length.\tDuring relaxation, the cross bridge between the actin and myosin break.\tCa++pumped back to sarcoplasmic cisternae.\tActin filament slide out of ‘A’ band and length of ‘I’ band increases. This returns the muscle to its original state.\tRepeated muscle contraction causes accumulation of lactic acid, produced from anaerobic breakdown of glycogen leads to muscle fatigue.\tMuscle contains red coloured oxygen storing pigment called myoglobin.\tMuscle with myoglobin called red muscle fibres, they are also contain large number of mitochondria which can utilize large amount of oxygen stored in them for ATP production also called aerobic muscle.\tSome muscles possess very less quantity of myoglobin and less mitochondrion hence called white fibres. Amount of sarcoplasmic reticulum is high in these muscles. They depend on anaerobic process for energy.


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