events at a neuromuscular junction

• Events at a neuromuscular junction:

  1. AP waves along axon towards synaptic knob 
• 1. Voltage sensitive Ca+ channels open and ca+ flood in via facilitated diffusion down electrochemical gradient 
  2. Vesicles move and fuse with presynaptic membrane 
• 4. Acetylcholine diffuses across cleft

  5. Complementary binding of acetylcholine to Na+ receptor mediated channels - causing them to open

  6. Depolarisation - Na+ flood in
• 7. generates AP across sarcolemma 

  8. Wave of depolarisation goes deep into muscle fibre down the t - tubules

  9. Change in voltage down t-tubule - voltage sensitive Ca+ in the sarcoplasmic reticulum open 
• 10. Ca+ move out of sarcoplasmic reticulum and into sarcolemma 

  11. Ca+ bind to troponin - muscle contraction triggered 
• Resetting the neuromuscular junction:

  1.) to remove Ca+ from presynaptic knob - Ca+ is pumped out (atp required) - this stops vesicles fusing so acetylcholine cannot be released

  2.) to remove acetylcholine from receptor site - acetylcholine esterase hydrolyses the acetylcholine in the receptor site causing Na+ gates to close so no more depolarisation

  3.) Ca+ is pumped back into sarcoplasmic reticulum (atp required)