Final answer:
Acetylcholine (ATC) is released by neurons at a cholinergic synapse and diffuses across the synaptic cleft to attach to nicotinic or muscarinic receptors on the next cell, leading to changes in the post-synaptic cell's activity.
Step-by-step explanation:
ATC, or acetylcholine, is the neurotransmitter released by neurons at a cholinergic synapse. When an action potential reaches the axon terminal, acetylcholine is released into the synaptic cleft, which is the space between the neuron and the next cell. Then, acetylcholine diffuses across the synaptic cleft and attaches to either nicotinic or muscarinic receptors on the post-synaptic cell. This binding changes the permeability of the post-synaptic membrane to specific ions, leading to either excitation or inhibition of the post-synaptic neuron.