Muscular System

• Action potential

  1. ACh released into neuromuscular junctions

  2. ACh opens ligand-gated Na+ channels on muscle fibers

  3. Na+ enters the muscle fibers and creates graded potentials

  4. Depolarization runs down T-tubules, causing voltage-gated Ca+ channels to open on the sarcoplasmic reticulum

  5. Ca+ is released from the sarcoplasmic reticulum and binds to troponin, removing it from tropomyosin

  6. Triggers muscle contraction
• Z-lines

  • End of sarcomere
• I-band

  • Zone with only thin filament
• H-zone

  • Zone with only thick filament
• A-band

  • Zone with thin and thick filament
• Thick filaments

  Made up of myosin
• Thin filaments

  Made up of actin
• Power stroke

  Myosin releases ADP and Pi to enter a low-energy conformation
• Twitch

  1. Latent phase: action potential travels down T-tubule, causing voltage-gated Ca+ channels to open

  2. Contraction phase: Ca+ combine with troponin to uncover the actin binding site, cross bridges form, and the H-zone shrinks

  3. Relaxation phase: Ca+ is actively pumped back into the sarcoplasmic reticulum
• The purpose of intercalated discs are to allow cardiac muscles to contract in a coordinated manner