Myofibril
tightly packed filament bundles found within skeletal muscle fibers
Myofibrils are elongated structures found within muscle fibers (cells) and are responsible for generating contraction of the muscle. They are composed of myofilaments, which are the contractile protein filaments of the muscle cell. There are two types of myofilaments: actin (thin) filaments and myosin (thick) filaments. The patterns of these filaments repeating along the length of the myofibril create the distinct striations seen in muscle tissue.
The sliding filament theory explains how muscle contraction occurs. During contraction, the myosin heads of the thick filaments bind to the thin filaments made up of actin by forming cross-bridges. The myosin heads then pull on the actin filaments, causing them to slide past the myosin filaments, which results in the muscle fiber shortening. This process requires calcium ions, which are released from the sarcoplasmic reticulum (a specialized type of endoplasmic reticulum in muscle cells) upon stimulation by an action potential. ATP is also utilized to power the cross-bridge formation and movement.
Overall, myofibrils are essential for muscle contraction, and their structure and function contribute to the overall strength, power, and endurance of our muscles.
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