Lecture Notes: Muscle Contraction

Overview

• Focus on the process of muscle contraction.
• Key components: Actin and myosin filaments.
• Importance of ATP and calcium ions.

Actin and Myosin Filaments

• Myosin Filaments: Have heads that form cross bridges with actin filaments.
  • Resemble little ratchets that attach to actin and pull them along.
• Actin Filaments: Serve as binding sites for myosin heads.

The Role of ATP in Muscle Contraction

1. Cross Bridge Formation:
   • Myosin heads attach to actin filaments when no ATP is present.
2. ATP Binding:
   • ATP (Adenosine Triphosphate) binds to myosin heads, causing detachment from actin.
3. ATP Hydrolysis:
   • ATP is hydrolyzed to ADP (Adenosine Diphosphate) and inorganic phosphate.
   • This hydrolysis causes the myosin head to change angle and reattach to a new position on actin.
4. Power Stroke:
   • ADP and phosphate release leads to the myosin head moving, pulling the actin filament.
   • This movement is called the power stroke.

Muscle Fiber Contraction

• Sarcomere Shortening: Repeated cycles of attaching, moving, and detaching result in muscle contraction.

Role of Calcium Ions

• Calcium ions are crucial for muscle contraction.
• Released by the sarcoplasmic reticulum in response to motor neuron signals.

Proteins Involved

1. Tropomyosin:
   • A protein that wraps around actin filaments, potentially blocking myosin binding sites.
2. Troponin:
   • Binds calcium ions, causing a shift in tropomyosin that exposes myosin binding sites.

Conclusion

• Calcium ions and ATP are essential for muscle contraction.
• No calcium = no contraction.

• Please review the process described for a deeper understanding of muscle contraction.
• Reflect on the function of calcium besides supporting healthy bones and teeth.

• Video question to consider: Answer is C for cowboy.

Have a nice day and refer to these notes for a comprehensive understanding of muscle contraction.