Skeletal muscle and sarcomere structure, the sliding-filament theory of contraction, and the role of ATP and calcium.
Skeletal (striated) muscle moves the body. Muscles work in antagonistic pairs (e.g. biceps and triceps) because they can only pull, not push — one contracts while the other relaxes.
Muscle structure
A muscle is made of muscle fibres, each containing many myofibrils. Myofibrils are divided into repeating units called sarcomeres, which contain two protein filaments: thick myosin and thin actin. Their overlap gives muscle its striped (striated) appearance. Each sarcomere runs between two Z-lines; the region of only actin is the I-band, the region containing myosin is the A-band.
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