Within a skeletal muscle, which component directly makes up a sarcomere and participates in contraction?

• A. Myofilament
• B. Sarcomere
• C. Myofibril
• D. Muscle Fiber

Answer: (A)

The contractile proteins themselves are the myofilaments, and they directly form a sarcomere and drive its contraction. Within a sarcomere, the thick filaments (myosin) and thin filaments (actin) slide past one another to shorten the unit. This is the essence of the sliding filament mechanism, powered by ATP, that produces muscle contraction.

Other structures exist at higher organizational levels: a sarcomere is the smallest contractile unit, a myofibril is a bundle of many sarcomeres arranged in a chain, and a muscle fiber is composed of many myofibrils. So the elements that actually make up the sarcomere and participate in its shortening are the myofilaments.