Anatomy and Physiology - Muscle Lecture 3 Notes

Lecture Overview

• Instructor: Bob Long
• Course: Anatomy and Physiology (Part 1)
• Focus: Structure of Sarcomere and Myofilaments (Actin and Myosin)

Key Concepts

Muscle Structure Recap

• Muscle structure hierarchy:
  • Muscle > Fascicle > Muscle Cell > Myofibril

Myofibril Structure

• Focus on sarcomere structure and function.
• Sarcomeres are repeating subunits within myofibrils.
• Comprised of proteins actin (thin filament) and myosin (thick filament).

Sarcomere Components

• Z Line:
  • Zigzag shaped line marking boundaries of the sarcomere.
  • Plate of proteins anchoring actin filaments.
• M Line:
  • Opposite to Z line, anchoring myosin filaments.

Bands and Zones

• I Band:
  • Contains only actin filaments.
  • Appears as a light band under isotropic light.
• A Band:
  • Contains overlapping actin and myosin filaments.
  • Appears as a dark band and includes:
    • Zone of Overlap: Where actin and myosin overlap.
    • H Zone: Contains only myosin.

Historical Context

• Terms "I" and "A" bands are derived from early studies using isotropic light.
  • Isotropic (light bands) and Anisotropic (dark bands) refer to light behavior on filaments.

Sarcomere Function

• Functional unit of muscle contraction.
• Sliding filament theory:
  • Myosin heads attach and pull on actin filaments.
  • Contraction shortens the sarcomere, then myofibril, muscle cell, and overall muscle.
  • Process involves coordinated contractions across multiple sarcomeres.

Next Steps

• Upcoming Videos:
  • Detailed molecular structure of actin and myosin.
  • Steps of muscle contraction.
  • Muscle performance.
• Quizzes follow each section for enrolled students.

Conclusion

• Understanding sarcomere structure is key to grasping muscle contraction.
• Further exploration in subsequent lectures.