AD

Muscle contraction steps

Steps to Muscle Contraction

1. Nerve Impulse Initiation

  • A nerve impulse travels to the neuromuscular junction on a muscle cell.

  • The neuromuscular junction is the point where the axon of the nerve meets the muscle cell.

2. Ach Release

  • Acetylcholine (Ach) is released from the axon into receptors located on the sarcolemma (muscle cell membrane).

3. Depolarization of Sarcolemma

  • The binding of Ach leads to the depolarization of the sarcolemma by opening ion channels.

  • This allows Na+ ions to enter the muscle cell.

4. Na+ Ion Diffusion

  • Na+ ions diffuse into the muscle fiber, causing further depolarization.

5. Action Potential Generation

  • This depolarization creates a wave of action potential, generating an electrical current across the sarcolemma.

6. Action Potential Propagation

  • Action potential travels across the sarcolemma and down the T-tubules.

  • This triggers the sarcoplasmic reticulum (SR) to release Ca+ ions.

7. Calcium Ion Binding

  • As Ca+ levels rise, Ca+ ions bind to Troponin.

  • This binding removes the blocking action of Tropomyosin from the actin binding sites, exposing them.

8. Cross Bridge Formation

  • Myosin is now ready to bind with actin, forming cross bridges that initiate the contraction process.

9. ATP Binding

  • To contract, ATP binds to the myosin.

10. ATP Hydrolysis

  • ATP is hydrolyzed (broken down) into ADP and inorganic phosphate (Pi), providing energy for myosin to assume a high-energy position (cocking of the head).

11. Cross Bridge Action

  • Actin and myosin bind together, forming a cross bridge.

12. Filament Sliding

  • The myosin heads pull the actin filaments inward, releasing ADP and Pi in the process, and return to a low energy position.

Continuation of Contraction

  • The myosin is now ready for more ATP to bind and repeat the entire cycle.

  • This contraction process continues as long as there are Ca+ ions and ATP available.