The Functional Unit of Contractile System in a Striated Muscle is Sarcomere.

Sarcomere is the basic functional unit of the contractile system in striated muscle. It is a highly organized structure that is responsible for muscle contraction. It is made up of two types of protein filaments - thick filaments made of myosin and thin filaments made of actin, tropomyosin, and troponin.

Structure of Sarcomere:

• Z-disc: It is a thin disc-like structure that serves as the boundary of each sarcomere.

• I-band: It is a light area between two A-bands, which consists of only thin filaments.

• A-band: It is a dark area in the middle of the sarcomere, which consists of both thick and thin filaments.

• H-zone: It is a light area in the middle of the A-band, which consists of only thick filaments.

• M-line: It is a thin line in the middle of the H-zone, which holds the thick filaments together.

Working of Sarcomere:

• During muscle contraction, the sarcomere shortens as the thin filaments slide over the thick filaments.

• This sliding is made possible by the cross-bridges formed between the myosin heads and actin.

• The cross-bridges are formed when calcium ions bind to troponin, which causes tropomyosin to move, exposing the binding site on actin.

• The myosin head then binds to the actin, forming a cross-bridge.

• The myosin head then swivels, pulling the thin filament towards the center of the sarcomere.

• The ATP is then used to detach the myosin head from the actin, and the cross-bridge is broken.

Conclusion:

In conclusion, the sarcomere is the basic functional unit of striated muscle and is responsible for muscle contraction. It is made up of protein filaments and has a highly organized structure that allows for the sliding of the filaments during muscle contraction. The cross-bridges formed between the myosin heads and actin are responsible for this sliding.