Skip to main content
Back

Muscle Tissue and Physiology - Anatomy & Physiology

Control buttons has been changed to "navigation" mode.
1/23
  • Properties of muscle tissue
    • Electrical excitability: respond to stimuli
    • Conductivity: conduct electrical impulses
    • Contractility: shorten to produce force
    • Extensibility: stretch without damage
    • Elasticity: return to original shape
    • Convert chemical energy (ATP) to mechanical energy
  • Types of muscle tissue
    • Skeletal muscle: striated, voluntary, multinucleated, cylindrical, unbranched
    • Cardiac muscle: striated, involuntary, branched, uninucleated, intercalated discs
    • Smooth muscle: non-striated, involuntary, uninucleated, spindle-shaped
  • Connective tissue layers of skeletal muscle
    • Epimysium: surrounds whole muscle
    • Perimysium: surrounds fascicles (bundles of muscle fibers)
    • Endomysium: surrounds individual muscle fibers
  • Muscle fiber components
    • Sarcolemma: muscle cell membrane
    • Sarcoplasm: cytoplasm
    • Myofibrils: protein bundles inside fiber
    • Sarcoplasmic reticulum: stores calcium ions
    • T-tubules: transmit signals into fiber
  • Myofilaments in muscle fibers
    • Thick filaments: myosin protein
    • Thin filaments: actin, tropomyosin, troponin
    • Elastic filaments: titin protein, anchor thick filaments and prevent overstretching
  • Function of troponin and tropomyosin
    • Troponin: binds calcium and moves tropomyosin
    • Tropomyosin: blocks myosin binding sites on actin when muscle is relaxed
  • Striations in skeletal muscle
    • A-band: dark band, contains thick and thin filaments, includes H-band (thick filaments only)
    • I-band: light band, contains thin filaments and Z-disc (anchors filaments)
  • Neuromuscular junction (NMJ) components
    • Synaptic knob: axon terminal with synaptic vesicles
    • Synaptic cleft: gap between nerve and muscle fiber
    • Acetylcholine (ACh): neurotransmitter released to stimulate muscle
    • ACh receptors: on sarcolemma bind ACh
    • Acetylcholinesterase: enzyme that breaks down ACh
  • Resting membrane potential of muscle fiber
    Approximately \(-90\,mV\), maintained by sodium-potassium pumps, with more negative charge inside the cell.
  • Depolarization and repolarization in muscle fibers
    • Depolarization: Na+ gates open, Na+ enters, inside becomes positive
    • Repolarization: Na+ gates close, K+ gates open, K+ exits, inside returns to negative
  • Excitation-contraction coupling
    Action potential spreads along sarcolemma and T-tubules, triggering Ca2+ release from sarcoplasmic reticulum, which binds to troponin and exposes active sites on actin.
  • Sliding filament theory steps
    1. Myosin head hydrolyzes ATP and cocks
    2. Myosin binds actin forming cross-bridge
    3. Power stroke pulls thin filament
    4. Myosin releases ADP and phosphate
    5. New ATP binds, myosin releases actin
    6. Cycle repeats
  • Muscle relaxation process
    • Stop nerve signals; ACh release ceases
    • ACh broken down by acetylcholinesterase
    • Ca2+ pumped back into sarcoplasmic reticulum using ATP
    • Troponin releases Ca2+, tropomyosin blocks active sites
    • Muscle returns to resting length
  • Length-tension relationship
    Muscle tension depends on muscle length before contraction; optimal resting length produces strongest contraction due to ideal overlap of thick and thin filaments.
  • Motor unit definition
    A motor neuron and all the skeletal muscle fibers it innervates, allowing coordinated contraction of multiple fibers.
  • All-or-none law in muscle fibers
    A muscle fiber contracts fully or not at all when stimulated to threshold voltage.
  • Twitch phases
    • Latent period: delay between stimulus and contraction
    • Contraction phase: cross-bridge formation and tension buildup
    • Relaxation phase: Ca2+ reentry into SR and tension decline
  • Isometric vs isotonic contraction
    • Isometric: muscle tension without change in length
    • Isotonic: muscle changes length while maintaining tension
  • Cardiac muscle characteristics
    Striated, branched, involuntary, with intercalated discs containing gap junctions and desmosomes; can contract without nervous stimulation due to pacemaker cells.
  • Smooth muscle contraction triggers
    Involuntary contraction triggered by Ca2+ mostly from extracellular fluid, no troponin but calmodulin regulates contraction.
  • ATP sources for muscle metabolism
    • Anaerobic fermentation: produces ATP without oxygen but yields lactic acid
    • Aerobic respiration: produces more ATP with oxygen, less toxic byproducts
  • Phosphagen system
    Immediate ATP supply by transferring phosphate groups from creatine phosphate or ADP to form ATP, controlled by enzymes myokinase and creatine kinase.
  • Oxygen debt
    Extra oxygen consumed after exercise to restore oxygen reserves, replenish phosphagen system, and oxidize lactic acid.