Sliding-Filament Theory

Thus, muscle, fiber, and myofibrils change lengths, but not myofilaments.

Processes of Muscle Contraction:

1. Nerve impulse moves down T-tubule depolarizing the tubules.
2. Ca++ is released from the lateral sacks of the Sarcoplasmic Reticulum into the Sarcomere among the Myofilaments.
3. Ca++ binds with Troponin located on Tropomyosin causing active attachment sites to be exposed.
4. Energized Myosin head attaches to exposed site on Actin filaments, attachment causes head deflection resulting in tension production (pulling action).
5. Available ATP re-energizes Myosin head, thus breaking Myosin head attachment to Actin filament (breaking the cross-bridge).

• As attached heads release other heads are attaching and deflecting causing muscle tension through its range of motion.
• If impulse is removed Ca++ is actively pumped back into Lateral Sacks allowing Troponin to cover active sites of Actin filament.
• CONTRACTION WILL ONLY CONTINUE if there is available Ca++ in the Sarcomere and ATP is available for use.