Lecture Notes: Myofibrils in Skeletal Muscle

Introduction

• Focus on the myofibril within skeletal muscles.
• Myofibril exhibits a pattern of dark and light bands.

Myofibril Structure

• Encompasses the entire skeletal muscle in length and breadth.
• Internal components like the nucleus and mitochondria are present but not shown in simplified diagrams.

Visualizing Myofibrils

• Transmission Electron Micrograph (TEM) shows the pattern of myofibrils.
• Myofibrils are the contractile units of skeletal muscle.

Dark and Light Band Pattern

• Dark and light bands visible in TEM.
• Dark areas formed by thick protein filaments (myosin).
• Light areas formed by thin protein filaments (actin).
• Thickness of protein filaments causes variation in band appearance:
  • Thick filaments = dark bands.
  • Thin filaments = light bands.

Key Protein Filaments

• Myosin: Thick protein filaments, responsible for the dark appearance.
• Actin: Thin protein filaments, responsible for the light appearance.

Structural Components

• Z Line: Perpendicular structure running along actin filaments; holds actin in place.
• M Line: Structure that holds myosin filaments in place.
• Sarcomere: Distance between two Z lines.

Importance of Structure

• Z lines play a crucial role in muscle contraction, to be discussed further in subsequent lectures.

Conclusion

• Understanding the structure of myofibrils is essential for comprehending muscle contraction mechanisms.