- Tropomyosin is a strand-like protein that wraps around the actin filament and blocks the myosin binding sites on actin.
- Troponin is a globular molecule sitting on top of tropomyosin and has calcium ion (Ca²⁺) binding sites.
- Muscle contraction occurs when myosin heads bind to actin, forming crossbridges, causing filaments to slide over each other without changing their length.
- The binding sites on actin are blocked by tropomyosin; myosin requires energy to bind and move actin.
- Calcium ions (Ca²⁺) bind to troponin, causing tropomyosin to shift and expose the myosin binding sites on actin.
- Calcium acts as a regulatory molecule for muscular contraction.
- Calcium is released when the muscle cell becomes depolarized.
- A resting muscle cell is polarized; an action potential from a motor neuron triggers depolarization via acetylcholine.
- The depolarization wave travels into the muscle fiber interior through transverse tubules (T-tubules).
Parent Tip: Review the logic above to help your child master the concept of sliding filament theory worksheet.
