Neuromuscular junction

1. How is acetylcholine stored in the presynaptic region? How many ACh molecules are in a quanta?
2. What is the synaptic cleft and what enzyme can be found in this region?
3. What is a miniature endplate potential (MEPP)?
4. How is an endplate potential (EPP) formed?
5. What is the safety factor?

Answers:
1. ACh is stored in three storage compartments (main --> mobilized --> immediate), where it is contained in packets called quanta. Each quanta has 5,000-10,000 ACh molecules. The immediate store contains 1,000 quanta.
2. This is the space between the presynaptic and postsynaptic region. It contains the enzyme ACh-esterase.
3. A MEPP is formed during a period of inactivation and it occurs when there is a spontaneous release of a quanta, which occurs every 5 seconds.
4. An EPP is formed when depolarization of the nerve opens up voltage-gated Ca channels, which floods the nerve terminal. This leads to the release of multiple quanta.
5. The safety factor refers to the initial excess amplitude of the EPP (4x needed for an AP), which allows time for ACh to move from the main and mobilizing storage to the immediate storage.