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Muscle Tissue Notes (Overview & Types)

Muscle Tissue Overview

  • Properties: contractile, conductive, elastic, extensible, and excitable (stimulated by a nerve impulse).
  • Functions: movement (voluntary body part motion), heart contraction, propulsion of materials through digestive and urinary tracts.
  • Vascularization: well-vascularized.
  • Types: skeletal, cardiac, smooth.

Skeletal Muscle Tissue

  • Also known as striated or voluntary muscle tissue.
  • Primary role: movement of the skeleton; can move some nonskeletal structures (e.g., facial skin, external urethral and external anal sphincters).
  • Thermoregulation: contraction generates heat, increasing body temperature.
  • Structure:
    • Long, cylindrical fibers arranged in parallel bundles (often run the length of the muscle).
    • Multinucleated cells with nuclei located at the periphery of the fiber.
    • Striations visible under light microscopy due to overlapping thick and thin filaments.
  • Innervation: voluntary; typically controlled by the somatic nervous system.
  • Regeneration: limited capacity for repair via cell division.
  • Additional notes: highly organized for forceful, precise movements.

Cardiac Muscle Tissue

  • Location: confined to the myocardium (thick middle layer of the heart wall).
  • Function: pumping action of the heart to move blood through the cardiovascular system.
  • Structure:
    • Relatively short, branched (bifurcated) cells.
    • 1–2 centrally located nuclei (1–2 centrally located nuclei).
    • Striations due to same filament arrangement as skeletal muscle.
  • Intercellular connections: intercalated discs (desmosomes and gap junctions) that strengthen connections and enable rapid electrical conduction.
  • Innervation: involuntary; contractions initiated by pacemaker cells in the heart.
  • Regeneration: minimal regenerative capacity; damaged cardiac tissue is not readily replaced.

Smooth Muscle Tissue

  • Also called visceral or involuntary muscle tissue.
  • Location: walls of most viscera (e.g., intestines, stomach, airways, urinary bladder, uterus, blood vessels); also in specialized structures like the iris.
  • Structure:
    • Non-striated (lacks visible striations).
    • Fusiform (spindle-shaped) cells; relatively short.
    • Single centrally located oval nucleus per cell.
  • Innervation: involuntary; not under conscious control.
  • Function: propels material through organs and regulates lumen size.
  • Regeneration: capable of cell division for growth and healing.