Anatomy and Physiology Chapter 10: Muscle Tissue

Introduction

• Focus on muscle tissue details
• Repetition of content for better understanding
• Three main types of muscle:
  • Skeletal Muscle: Voluntary, focus of this chapter
  • Cardiac Muscle: Involuntary, found in the heart
  • Smooth Muscle: Involuntary, lines hollow organs

Skeletal Muscle Overview

• Specialized for contraction
• Moves body by pulling on bones
• Supports posture, body position, and soft tissues
• Guards body entrances/exits, maintains temperature
• Stores nutrients

Anatomy of Skeletal Muscle

• Connective Tissue Layers:
  • Epimysium: Outermost layer, surrounds muscle
  • Perimysium: Surrounds muscle fiber bundles (fascicles)
  • Endomysium: Surrounds individual muscle cells/fibers
• Rich blood supply and nerves
• Collagen fibers from all layers converge to form:
  • Tendon: Attaches muscles to bone
  • Aponeurosis: Tendinous sheet

Muscle Fiber Structure

• Skeletal Muscle Fibers:
  • Large, multinucleate, and striated
  • Contain sarcolemma (cell membrane) and sarcoplasm (cytoplasm)
  • T-tubules transmit action potentials
  • Sarcoplasmic Reticulum (SR) stores/releases calcium
• Myofibrils: Subdivisions within muscle cells responsible for contraction
  • Myofilaments: Thin (actin) and thick (myosin) filaments

Sarcomere Structure

• Smallest functional unit of muscle fiber
• Arrangement of thin and thick filaments creates striations
• A Bands: Include M line, H band, and zone of overlap
• I Bands: Contain Z lines and titan proteins

Muscle Contraction: Sliding Filament Theory

• During contraction:
  • H and I bands narrow
  • Zones of overlap widen
  • Z lines move closer
• Thin filaments slide toward sarcomere center
• Action potentials trigger contractions

Neuromuscular Junction and Action Potentials

• Neuromuscular Junction (NMJ):
  • Synapse between neuron and muscle fiber
  • Release of acetylcholine (ACh) causes sodium influx & depolarization
  • Action potential spreads via T-tubules, releasing calcium
• Calcium binds to troponin, shifting tropomyosin, exposing active sites

Cross-Bridge Cycle

• Myosin heads bind to actin's active sites forming cross-bridges
• Power stroke pulls thin filaments towards center
• ATP binds to myosin, re-cocks the head for repeated cycles

Types of Muscle Contractions

• Isotonic Contractions: Muscle changes length
  • Concentric: Muscle shortens
  • Eccentric: Muscle elongates
• Isometric Contractions: Muscle length remains unchanged

Muscle Relaxation

• Elastic forces, opposing muscle groups, and gravity aid in relaxation
• Muscle tone maintains posture without movement

ATP and Muscle Metabolism

• ATP is primary energy source for contraction
• Muscle fibers store ATP and regenerate more during activity
• Oxygen debt occurs post-exercise

Muscle Performance

• Fast Fibers: Quick to contract, fatigue quickly
• Slow Fibers: Slow to contract, resist fatigue
• Intermediate Fibers: Have properties of both
• Muscle hypertrophy vs. atrophy

Aging and Muscle Tissue

• Muscle fibers shrink, become less elastic
• Fibrosis increases, recovery slows

Types of Muscle Fibers

• White Muscle (Fast Fibers): Quick contraction, low endurance
• Red Muscle (Slow Fibers): High endurance, more myoglobin

Summary and Review

• Understanding muscle fiber anatomy is crucial for grasping muscle function
• Repetition and visualization key to mastering this complex subject

Looking Ahead

• Chapter 12 will focus on the nervous system and its role in muscle control