MUSCLE NERVE CARTILAGE BONE
SKELETAL MUSCLE
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Myosin heads form cross bridges and pull thin filaments, causing them to slide.
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Both thick and thin filaments shorten as the muscle contracts.
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A bands bunch up and shorten as myosin heads attach to thin filaments.
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Myosin heads attach and detach from thin filaments, causing thin filaments to shorten.
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Detailed explanation-1: -Summary. According to the sliding filament theory, a muscle fiber contracts when myosin filaments pull actin filaments closer together and thus shorten sarcomeres within a fiber. When all the sarcomeres in a muscle fiber shorten, the fiber contracts.
Detailed explanation-2: -Cross-bridge theory states that actin and myosin form a protein complex (classically called actomyosin) by attachment of myosin head on the actin filament, thereby forming a sort of cross-bridge between the two filaments.
Detailed explanation-3: -The muscle contraction cycle is triggered by calcium ions binding to the protein complex troponin, exposing the active-binding sites on the actin. As soon as the actin-binding sites are uncovered, the high-energy myosin head bridges the gap, forming a cross-bridge.
Detailed explanation-4: -The first step in the process of contraction is for Ca++ to bind to troponin causing an interaction that slides tropomyosin away from the binding sites on actin filaments. This allows the myosin heads to bind to these exposed binding sites and form cross-bridges.