What is a sacromere?
contractile unit of a muscle fiber
A sarcomere is the smallest contractile unit of a muscle fiber. It is a highly organized arrangement of protein filaments that produces the contraction of skeletal and cardiac muscle. Each sarcomere consists of thick filaments (myosin) and thin filaments (actin) that are arranged in a repeated pattern along the myofibrils of the muscle fiber. The actin filaments are anchored at the Z-line, while the myosin filaments are staggered between the actin filaments, forming the A-band. The H-zone is the central portion of the A-band where only myosin filaments are present. The I-band is the region between the A-band and the Z-line that contains only actin filaments. The sarcomere shortens during contraction as the thick and thin filaments slide past each other, resulting in muscle contraction.
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Sarcomere: The Basic Unit of Muscle Contraction