Proteins · Part 2

and the sarcolemma of the muscle fibre is called the neuromuscular junction or motor end plate. When nerve impulse reaches a neuromuscular junction, acetylcholine is released. It initiates the opening of multiple gated channels in sarcolemma. The action potential travels along the T-tubules and triggers the release of calcium ions from the sarcoplasmic reticulum. The released calcium ions bind to troponin on thin filaments. The tropomyosin uncovers the myosin-binding sites on thin filaments. Now the active sites are exposed to the heads of myosin to form a cross-bridge (Figure . ). During cross-bridge formation actin and myosin form a protein complex called actomyosin. Utilizing the energy released from hydrolysis of ATP, the myosin head rotates until it forms a ° angle with the long axis of the filament. In this position myosin binds to an actin and activates a contraction – relaxation cycle which is followed by a power stroke. Figure . Composition of thick and thin filaments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contain several regulatory proteins like tropomyosin and troponin which help in regulating the contraction of muscles along with actin and myosin .