Sliding Theory of Muscle Contraction:

• The sliding filament theory is a widely accepted model that explains how muscle contraction occurs.

• According to this theory, during muscle contraction, thin actin filaments slide past thick myosin filaments, causing the sarcomeres (the contractile units of muscle fibers) to shorten.

• The sliding is facilitated by the cyclic interaction between myosin heads and actin filaments.

• The steps involved in muscle contraction include:

  1. Calcium ions (Ca²⁺) are released from the sarcoplasmic reticulum in response to a nerve impulse.

  2. Ca²⁺ ions bind to troponin, causing a conformational change in tropomyosin, exposing the binding sites on actin.

  3. Myosin heads (cross-bridges) bind to actin at these exposed sites.

  4. ATP is hydrolyzed to ADP and inorganic phosphate (Pi), providing energy for myosin to undergo a conformational change (the power stroke).

  5. This change in myosin’s shape causes the thin actin filaments to slide along the myosin filaments, shortening the sarcomeres and leading to muscle contraction.

  6. The cycle repeats as long as Ca²⁺ ions are present and ATP is available.