Lecture on Sliding Filament Theory by Heather

Introduction

• Presenter: Heather
• Topic: Sliding Filament Theory
• Key focus: Understanding muscle contraction at the microscopic level

Structure of Skeletal Muscle Fibers

• Striated Appearance: Bands observed under a microscope.
• Composition:
  • Actin: Thin filament.
  • Myosin: Thick filament containing myosin heads.

Muscle Contraction Process

• Initiation:
  • Triggered by action potential from the brain.
  • Influx of calcium ions.
  • Calcium binds to troponin on the actin filament.
  • Causes a conformational change exposing myosin binding sites.

Steps of the Contraction Cycle

1. Detachment:
   • Myosin head detaches from actin.
   • Requires ATP to bind to the myosin head.
   • Myosin enters a resting state.
2. Hydrolysis:
   • ATP split into ADP and phosphate.
   • Prepares myosin head to bind to actin.
3. Crossbridge Formation:
   • Myosin head binds to actin.
   • Both filaments are positioned correctly.
4. Power Stroke:
   • ADP and phosphate detach.
   • Myosin returns to relaxed shape.
   • Initiates movement of actin filaments.

Cycle Continuation

• ATP binding leads to detachment and cycle restart.
• Continues until movement ceases from lack of action potential.

Summary

• Cycle begins with detachment and ends with power stroke.
• Continues with ATP involvement.
• Ceases when brain stops action potential.