MEDICAL PHYSIOLOGY

Detailed explanation-1: -The functional unit of the contractile system of a striated muscle is sarcomere that is a repeating unit imparting striations to the striated muscles due to the presence of proteins that form thick and thin filaments .

Detailed explanation-2: -The functional unit of the contractile system in the striped muscle is sarcomere.

Detailed explanation-3: -The sarcomere is the smallest functional unit of a skeletal muscle fiber and is a highly organized arrangement of contractile, regulatory, and structural proteins. It is the shortening of these individual sarcomeres that lead to the contraction of individual skeletal muscle fibers (and ultimately the whole muscle).

Detailed explanation-4: -The portion of the myofibril between two successive ‘Z’ lines is considered as the functional unit of contraction and is called a sarcomere Sarcomere is considered as the functional unit of contraction in a muscle fibre. So, the correct answer is ‘Portion of a myofibril between two successive Z-lines’.