Dr Praveen Kumar Agrawal is teaching live on Unacademy Plus
Course: Locomotion and Movement -2 Lesson-10: Mechanism of contraction (Flow chart) DR. P. K. AGRAWAL M.Sc, PH.D., CSIR NET (JRF), SRF, GATE, FIAZ 20 Years of Pre-medical teaching experience Ex Faculty, Allen Career Institute, Kota Watch my Live Classes on Unacademy Plus
Mechanism of muscle contraction The contraction process begins when an impulse is given to a myofibre by a motor neuron. . T tubule receives the impulse and gives it to the L tubule. L Tubule in response open their calcium ion channels, releasing large number of calcium ions into the sarcoplasm. .The released calcium breaks up the TT complex, leading to exposure of active sites of actin. .Myosin head now combine with active site and ATP breakage occurs. . This generates energy for heads to tilt inwardly to draw actin filaments towards cenre (or towards M line) This shortens the sarcomere and contraction process occurs.
Impulse from a motor nerve Action potential develops in sarcolemma Action potential develops in T-tubule L-tubule releases Ca2 ions in sarcoplasm Actin filaments slide over myosin and contraction occurs Released Ca2 combine with troponin-C Myosin head tilt and pull actin filaments towards them A conformational change irtroponintropomyosin complex Myosin head gets attached with active site of actin Myosin head breaks up ATP to derive energy Active sites of actin filaments become uncovered forming acto-myosin complex
Relaxation of muscle fibre During relaxation, all the events occur in reverse direction. . At the time of relaxation (when stimulation is terminated), the actomyosin complex is broken down and myosin heads get detached from actin filaments. This process involves the use of ATP. .At the same time, the calcium ions return back to L-tubule (in sarcoplasmic reticulum). This is also an active process that uses ATP. Due to disappearance of calcium ions, troponin-tropomyosin complex is again re- established, that again covers the active sites of actin filament. . Due to this the interaction between actin and myosin ceases to occur and thus the actin filaments return back to their original position. . This results in muscular relaxation. . Students should keep in mind that, like contraction, relaxation is also an active process (that requires the use of ATP). This is the basis of rigor mortis.
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