What is the most fundamental unit of muscle contraction?

The most fundamental unit of muscle contraction is the sarcomere. 

Sarcomere is the basic structural and functional unit of striated muscle fibers. A sarcomere is the segment of a myofibril that lies between two Z-lines. It contains organized arrangements of actin (thin) and myosin (thick) filaments. During muscle contraction, these filaments slide past each other, leading to the shortening of the sarcomere. As sarcomeres contract together in large numbers, the entire muscle fiber shortens, resulting in muscle contraction. Therefore, sarcomeres are the smallest repeating units responsible for the contractile activity in skeletal and cardiac muscles.




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