Skeletal muscle cells are stimulated by the motor neurons of the somatic nervous system”. The reception of the motor stimulus (action potential) opens the calcium channels allowing calcium which is stored in the SR to be released. The release of calcium causes the release of acetylcholine-Ach (neurotransmitter). The calcium binds to the troponin on the actin filament. Troponin then regulates the tropomyosin which obstructs binding sites for myosin. This allows the tropomyosin to move, unblocking the bonding site. Myosin then binds to the unblocked site on the actin and applies a pull. This will pull the Z bands towards each other thus shortening the sarcomere, causing muscle contraction. However, as calcium is released, the “ATP-dependent calcium pump is activated” and it continuously pumps calcium back to the SR to be stored again. This leads to a drop in calcium level within the cytoplasm. When the calcium level is too low, the calcium binding action to troponin is terminated, releasing tropomyosin which again blocks the binding site.

Della Mariya Davis

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