Chapter 9: Muscles & Muscle Tissue Summary

Muscle Similarities

  • Skeletal and smooth muscle fibers are elongated.
  • Contraction depends on myofilaments: actin and myosin.
  • Terminology: sarcolemma (muscle membrane), sarcoplasm (muscle cell cytoplasm), "myo", "mys", "sarco" (muscle terms).

Skeletal Muscle Tissue

  • Characteristics: Striated, voluntary, multi-nucleate, powerful.
  • Responsible for body motility.

Cardiac Muscle Tissue

  • Characteristics: Striated, involuntary, uninucleate, intercalated discs.
  • Contracts at steady rate from pacemaker.

Smooth Muscle Tissue

  • Characteristics: Non-striated, involuntary, uninucleate.
  • Found in hollow organs (stomach, blood vessels).

Muscle Functions

  1. Locomotion (skeletal).
  2. Pumping blood (cardiac).
  3. Propelling substances (peristalsis).
  4. Maintain posture.
  5. Stabilize joints.
  6. Generate heat.

Special Muscle Tissue Characteristics

  • Excitability: Responsive to stimuli.
  • Contractility: Shortens when stimulated.
  • Extensibility: Ability to be stretched.
  • Elasticity: Recovers to resting length.

Structure of Skeletal Muscle

  • Epimysium: surrounds entire muscle.
  • Perimysium: surrounds fascicles (bundles).
  • Endomysium: surrounds individual fibers.

Contraction Mechanism

  • Sliding filament model: actin and myosin overlap during contraction.
  • Sarcomeres: functional units between Z discs.
    • Thick filaments (myosin) and thin filaments (actin).

Excitation-Contraction Coupling

  • Action potential travels along sarcolemma and T tubules.
  • Triggers Ca²⁺ release from sarcoplasmic reticulum.
  • Ca²⁺ binds to troponin, allowing actin-myosin interaction.

Motor Units

  • Consist of a motor neuron and the fibers it innervates.
  • Smaller units for fine control; larger for strength.

Muscle Responses

  • Twitch: three phases (latent, contraction, relaxation).
  • Graded responses based on stimulation frequency and strength.

Energy for Contraction

  1. ATP: immediate energy source.
  2. Creatine phosphate: quick regeneration of ATP.
  3. Anaerobic glycolysis: short bursts of activity.
  4. Aerobic respiration: sustained activity.

Types of Muscle Fibers

  • Slow oxidative fibers: endurance.
  • Fast oxidative fibers: intermediate activities.
  • Fast glycolytic fibers: short, intense bursts.

Effects of Exercise

  • Aerobic: increases endurance & resistance to fatigue.
  • Resistance: muscle hypertrophy & strength increases.

Muscle Fatigue

  • Causes include ionic imbalances, prolonged activity, and lack of ATP.

Muscle Tone

  • Constant, slightly contracted state; helps maintain posture.