How does neuromuscular transmission occur in myasthenia gravis (MG)?

Updated: Aug 27, 2018
  • Author: Abbas Jowkar, MD; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Answer

The following physiologic events occur in neuromuscular transmission:

  1. A nerve action potential propagates down the axon and depolarizes the presynaptic nerve terminal.
  2. Voltage-gage calcium channels open in response to depolarization and there is calcium influx through these channels into the nerve terminal.
  3. Synaptic vesicles fuse with the presynaptic membrane, releasing ACh into the synaptic space.
  4. ACh molecules bind to AChR on the post-synaptic membrane causing the the recepors to undergo conformational change, opening the ion channel.
  5. Membrane conductance to Na+ ions increases (Na+ goes in, K+ goes out) resulting in depolarization of endplate region causing end-plate potenital (EPP).
  6. If the EPP is sufficient to depolarize the adjacent muscle membrane to threshold, an action potential is generated in the muscle fiber. Conversely, if it is of insufficient magnitude it will not cause the muscle membrane to reach threshold, and therefore fails to generate a muscle fiber action potential.

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