Understanding Muscle Tissue Structure and Function

Nov 19, 2024

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