The functional unit of myofibril lies in between

The functional unit of myofibril is a sarcomere, and it plays a critical role in the contraction and relaxation of muscles. Here's a detailed explanation:

1. Structure of a Sarcomere:
   • A sarcomere is a repeating segment in a myofibril and lies between two Z-lines.
   • It consists of two types of protein filaments:
     • Actin filaments (thin filaments): Anchored to the Z-line.
     • Myosin filaments (thick filaments): Positioned in the center of the sarcomere.
2. Components of a Sarcomere:
   • Z-Line (Z-Disc): The boundary of a sarcomere where actin filaments are attached.
   • M-Line: The central region where myosin filaments are anchored.
   • I-Band: The lighter region containing only actin filaments.
   • A-Band: The darker region where actin and myosin filaments overlap.
   • H-Zone: The central region of the A-band containing only myosin filaments.
3. Muscle Contraction:
   • When a muscle contracts, the sarcomere shortens as actin and myosin filaments slide past each other. This is known as the sliding filament theory.
   • The Z-lines move closer together, and the H-zone becomes narrower during contraction.
4. Significance:
   • The functional unit of myofibril is the sarcomere because it is directly responsible for the generation of force during muscle contraction.

Key Points in Solution

• The sarcomere is the repeating segment between two Z-lines in a myofibril.
• It contains thin (actin) and thick (myosin) filaments that interact to produce muscle contraction.
• The sliding of these filaments within the sarcomere enables the muscle to contract efficiently.