The figure below shows the two main families of acetylcholine receptors: muscarinic and nicotinic. In structural terms, muscarinic receptors are G-coupled protein receptors, while nicotinic receptors are ligand-gated ion channels. They can be found on both sides of the synaptic cleft (presynaptic and postsynaptic).
After the pressure drops below 40 psi, the electrical switch turns on the pump and the pressure in the tank increases. Any failure in any component or loss of electricity can cause a well to suddenly stop producing water when a faucet is turned on.
Unscrew the aerator body from the faucet and remove all the internal components. Clean and reassemble. If you get weak water flow when you turn on the faucet, don't assume your water pressure has suddenly gone bad. You could simply have a filter screen, or aerator, that's clogged.