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Unformatted text preview: Muscle contraction When a nerve impulse arrives at the muscle cells, it passes across the neuromuscular junction and enters the muscle cell membrane, which is known as the sarcolemma. The impulse spreads across the muscle cell and enters its cytoplasm, which is called sarcoplasm . The nerve impulse causes the actin filaments to slide across the surface of the myosin filaments. The sliding filaments pull together the ends of the muscle cell, thereby causing it to contract. The sliding filaments require that calcium ions and energy in the form of ATP be available. Two proteins called tropomyosin and troponin also function in the contraction. Cross-bridges hold the filaments together as the muscle contracts. After the contraction has taken place, the energy to sustain the contraction is used up, and the cross-bridges break. The filaments then slide back to their original position, and the muscle cell cross-bridges break....
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- Fall '07