What are the primary, secondary, and tertiary groups of synaptic vesicles for 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 primary, or immediately available store consists of approximately 1000 quanta of ACh and are located just beneath the pre-synaptic nerve terminal membrane at specific sites called active zones. These release sites (active zones) lie directly opposite the ACh receptors (AChRs) located on the post-synaptic membrane. The primary store is available for immediate release. They behave like soldiers at the front line, ready for action.

The secondary, or mobilization store consists of approximately 10,000 quanta of ACh that can replenish the primary store after a few seconds. These behave like immediate reinforcements that become mobilized to replace the depleted primary store.

Finally, a tertiary, or reserve store of more than 100,000 quanta exists far from the NMJ in the axon and cell body. They behave like the reserves.

Voltage-gated calcium (Ca++) channels (P/Q-type) are located in the proximity of the active zones. Under the electron microscope they appear as double parallel rows of dense intramembrane particles.


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