Muscle Physiology Overview

Terminology

  • Muscle fiber vs Muscle Cell
  • Myo- = muscle
  • Sarco- = flesh
  • Sarcolemma
  • Sarcoplasm

Three Main Types of Muscle

  1. Skeletal
  • Striated, long muscle fibers, voluntary
  • Multinucleated
  • Function: moves bones
  • Location: everywhere
  1. Cardiac
  • Striated, branching cells, involuntary, intercalated discs
  • 1-2 centrally located nuclei
  • Function: pumps blood
  • Location: heart
  1. Smooth
  • Non-striated, involuntary, spindle-shaped cells
  • 1 central nucleus
  • Location: walls of hollow organs
  • Function: moves fluids, closes openings

Special Characteristics of Muscle Tissue

  • Excitability: Responds to stimuli (neurotransmitters)
  • Contractility: Ability to shorten
  • Extensibility: Ability to stretch
  • Elasticity: Ability to recoil

Muscle Functions

  • Producing Movement: e.g., moving bones, peristalsis
  • Maintaining Posture: Against gravity
  • Stabilizing joints: Muscle pulls bone, supports weight
  • Generating heat: Primarily through skeletal muscle

Skeletal Muscle Anatomy

  • Nerve Supply: Controlled by nerve endings, vascular supply required
  • Connective Tissue Sheaths:
  • Epimysium, Perimysium, Endomysium
  • Attachments:
  • Origin: immovable end
  • Insertion: movable end
  • Direct: epimysium attaches to periosteum
  • Indirect: via tendons or aponeurosis

Microscopic Anatomy

  • Sarcolemma: Plasma membrane, multinucleated
  • Sarcoplasm: Contains organelles, glycogen, myoglobin
  • Myofibrils: Composed of sarcomeres (functional unit)
  • Thick and thin filaments (actin and myosin) responsible for contraction

Excitation-Contraction Coupling

  • Nerve impulse triggers release of ACh
  • Action potential spreads across sarcolemma and T-tubules
  • Calcium release leads to muscle contraction

Muscle Contraction Types

  • Isometric: Muscle tension without movement
  • Isotonic: Muscle tension with movement
  • Concentric (muscle shortens)
  • Eccentric (muscle lengthens)

Muscle Metabolism

  • ATP required for muscle contraction and calcium pump
  • Energy Systems:
  • Direct phosphorylation, glycolysis, aerobic respiration
  • Fatigue Factors: Ionic imbalances, oxygen deficit, energy depletion

Smooth Muscle

  • Structure: Involuntary, spindle-shaped, lacks striations
  • Contraction Mechanism: Involves calcium binding to calmodulin
  • Types:
  • Single-unit: contracts as a unit, responds to chemical stimuli
  • Multi-unit: independent fibers, responds to nerve signals