Question

explain the steps in the sliding filament theory of muscle contraction, following the spreading of an action potential along the sarcolemma.

Answer 1

The sliding filament theory describes muscle contraction involving the release of calcium from the sarcoplasmic reticulum, the binding of calcium to troponin, the formation of cross-bridges between myosin and actin, and the power stroke powered by ATP. These events cause the actin filaments to slide over the myosin filaments, shortening the muscle fiber and resulting in contraction.

Step-by-step explanation:

The sliding filament theory explains muscle contraction as a sequential process:

1. An action potential travels along the sarcolemma and down the T-tubules.
2. This triggers the sarcoplasmic reticulum (SR) to release calcium ions (Ca2+) into the sarcoplasm.
3. Calcium ions bind to troponin, causing conformational changes that shift tropomyosin away from the myosin-binding sites on the actin filaments.
4. With the binding sites exposed, the myosin heads attach to actin forming cross-bridges.
5. The myosin heads then execute a power stroke, pulling the actin filaments towards the center of the sarcomere.
6. ATP binds to the myosin heads, causing them to detach from the actin, then it is hydrolyzed to reset the myosin heads for a new cycle.
7. This repeating cycle of cross-bridge attachment and power strokes causes the sliding of the actin filaments over the myosin filaments, shortening the sarcomeres and resulting in muscle contraction.

Overall, the critical steps of the theory are the release of calcium, formation of cross-bridges between actin and myosin, and the use of ATP to power the cycling of these molecular interactions, leading to muscle shortening and movement.