A neuron relays information to another neuron at a synapse. The neuron transmitting the information is called the pre-synaptic neuron, and the neuron receiving the information is the postsynaptic neuron. Let’s look at what happens at a cholinergic synapse, one of the most common types of synapses. When an action potential arrives at the synaptic knob of the pre-synaptic neuron, voltage-regulated calcium gates open, calcium ions enter and bind to synaptic vesicles. This leads to exocytosis which releases the neurotransmitter acetylcholine from the synaptic vesicles into the synaptic cleft. Acetylcholine molecules then diffuse across the synaptic cleft and bind to ACh receptors in the membrane of the postsynaptic neuron. The binding opens ion channels, and the membrane depolarizes. If this depolarization brings the initial segment of the postsynaptic neuron to threshold, it will result in an action potential. The depolarization of the postsynaptic membrane is short-lived because acetylcholinesterase rapidly breaks down the ACh in the synaptic cleft.