Functional Unit of Contraction in Muscles - Sarcomere
Sarcomere is the functional unit of contraction in muscles. It is the basic structural and functional unit of a myofibril, which is the contractile element of muscle fibers. Sarcomeres are repeated along the length of a myofibril and are responsible for muscle contraction.

Structure of Sarcomere
- Sarcomere is composed of thick and thin filaments that slide past each other during muscle contraction.
- Thick filaments are made of myosin protein, while thin filaments are made of actin, tropomyosin, and troponin proteins.
- The arrangement of these filaments gives sarcomere a striped appearance under a microscope, known as striations.

Mechanism of Muscle Contraction
- During muscle contraction, myosin heads attach to actin filaments and pull them towards the center of the sarcomere.
- This sliding of filaments shortens the sarcomere, leading to muscle contraction.
- The interaction between myosin and actin is regulated by calcium ions, which are released upon nerve stimulation.

Importance of Sarcomere in Muscle Function
- Sarcomeres play a crucial role in determining the length and force production of muscles.
- The ability of sarcomeres to contract and relax allows muscles to generate movement and perform various functions in the body.
- Understanding the structure and function of sarcomeres is essential for studying muscle physiology and pathologies.
In conclusion, sarcomere is the functional unit of contraction in muscles, where the interaction between thick and thin filaments leads to muscle contraction. Its structure and mechanism are essential for the proper functioning of muscles in the body.