Lecture Notes: Structure and Function of Muscle Tissue

Introduction

• Understanding muscle physiology is essential for training and programming in strength and conditioning.

Muscle Tissue Overview

• Muscle as an Organ: Contains muscle tissue, connective tissue, nerves, and blood vessels.
  • Connective tissue provides structure.
  • Nerves and blood vessels are crucial for function and waste removal.

Connective Tissue Layers

• Epimysium: Outermost layer.
• Perimysium: Surrounds muscle fascicles.
  • Fascicles are bundles of muscle fibers.
• Endomysium: Surrounds individual muscle fibers.
• These layers are continuous with the muscle tendon, allowing tension transmission.

Muscle Fiber Structure

• Muscle Fiber: Multi-nucleated due to large size.
  • Nuclei help manage cellular functions.
• Sarcoplasm: Muscle cell cytoplasm.
• Myofibrils: Contractile strands within the cell.
  • Composed of myofilaments (actin and myosin).

Motor Units

• Motor Unit: Functional unit comprising a motor neuron and all muscle fibers it innervates.
• Different muscle groups have different fiber counts per motor unit based on function.

Cellular Components of Muscle Fibers

• Mitochondria: Provides energy.
• T Tubules: Allow rapid action potential transmission.
• Sarcoplasmic Reticulum: Stores/releases calcium.
• Sarcolemma: Muscle cell membrane.

Sliding Filament Theory

• Explains contraction and tension generation.
• Sarcomeres: Contractile units within myofibrils.
  • Exhibit striated appearance due to actin and myosin overlap.
• Key Structures: Z lines, M line, H zone, A band, I band.

Muscle Contraction Process

• Power Stroke: Myosin heads bind to actin, creating contraction.
  • Requires calcium and ATP.

Phases of Muscle Contraction

1. Resting Phase: No action potential.
2. Excitation-Contraction Coupling: Action potential triggers calcium release.
3. Contraction Phase: Actin-myosin coupling and cross-bridge cycling.
4. Recharge Phase: ATP allows for continuation of contraction.
5. Relaxation Phase: Calcium uptake ceases contraction.

Key Points

• Force Production: Depends on number of actin-myosin cross-bridges.
• Calcium & ATP: Essential for contraction and relaxation.
• Muscle Size: Larger muscles have more contractile elements, producing more force.

Conclusion

• Understanding muscle physiology aids in logical training decisions.
• Next topic: Neuromuscular system and motor unit recruitment.

Dr. Goodin's Takeaway: Actin-myosin cross-bridge formation is crucial for muscle force production. Calcium and ATP are necessary for cross-bridge cycling. Larger muscles can produce more force due to more binding opportunities.

Next Steps: Explore neuromuscular systems in further lectures.