What do acetylcholinesterase inhibitors do?

Acetylcholinesterase (AChE) is a serine hydrolase whose primary function is to hydrolyze the neurotransmitter acetylcholine (ACh), breaking it down into acetic acid and choline. This terminates the signal that acetylcholine generates, hindering further communication between the neuron and muscle cell, leading to the relaxation of a muscle fiber.  

Acetylcholinesterase (AChE) inhibitors increase the concentration and duration of acetylcholine activity by obstructing acetylcholinesterase activity, preventing the hydrolysis and breakdown of acetylcholine into its components – acetic acid and choline. When acetylcholinesterase activity is inhibited, acetylcholine keeps accumulating in the synaptic cleft, prolonging its action and preventing the muscle from relaxing.