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.
When the water pressure drops to a certain level, the switch senses more water is needed, and spring-loaded electrical parts make contact, turning on the well pump. When the pressure returns to a preset level and the well tank is filled, the electrical contacts separate, and the well pump turns off.