Review of Neuromuscular Transmission

A. Synaptic activity - somewhere in motor cortex

  1. Integration of synaptic input - EPSPs vs. IPSPs
  2. Summation - temporal and spatial
  3. Depolarization of axon hillock
  4. Generation of action potential
  5. Conduction of AP down axon
  6. Depolarization of nerve terminal
  7. Influx of Ca++
  8. Release of neurotransmitter
  9. Activation of postsynaptic receptors
  10. Summation of EPSPs and IPSPs
  11. Begin process again

B. Sequence of events in spinal cord at the alpha-motor neuron

  1. Summation of EPSPs and IPSPs at alpha-motor neuron causes an AP at alpha-motor neuron axon hillock.
  2. Propagation of AP down neuron to nerve terminal
  3. AP causes release of acetylcholine at neuromuscular junction
  4. Acetylcholine binds to nicotinic receptors
  5. Activation of NACh receptors produces an end-plate potential.
  6. The EPP depolarizes membrane surrounding the end-plate causing the membrane potential to reach threshold.
  7. An action potential is generated in the membrane surrounding the end-plate.
  8. The action potential propagates the length of the muscle.
  9. The action potential enters the transverse tubules and causes release of Ca++ from the SR.
  10. Ca++ binds to troponin which causes tropomyosin to move off of the cross bridge binding site on actin.
  11. Cross bridge cycle begins and continues until Ca++ dissociates from troponin and is sequestered into SR
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