Question

The functional unit of contractile system in a striated muscle is

• A. sarcomere
• B. $Z$-band
• C. cross bridges
• D. myofibril

Answer 1

The Correct Option is A

To understand which option correctly identifies the functional unit of the contractile system in striated muscle, let's explore the options provided:

1. Sarcomere: The sarcomere is the basic structural and functional unit of striated muscle fibers. It is the segment between two neighboring Z-lines (or Z-discs), and it consists of actin and myosin filaments that slide over one another during muscle contraction. This sliding mechanism of filaments allows for muscle contraction, making the sarcomere the fundamental unit of muscle contraction.
2. Z-band: Also known as the Z-line, this is the boundary between sarcomeres. While it plays a role in organizing the sarcomere's structure, it is not the contractile unit itself.
3. Cross Bridges: These are formed by the interaction of myosin heads with actin filaments, essential for muscle contraction, but they are components within the sarcomere rather than functional units themselves.
4. Myofibril: This is a long, fibrous structure within muscle cells composed of repeating units of sarcomeres, but it is larger than the basic functional unit.

Thus, examining the roles of each element, the correct answer is:

Sarcomere is the functional unit of the contractile system in striated muscles.