The cholinergic system is characterized by the use of which transmitter as the primary signal?

• A. Acetylcholine
• B. GABA
• C. Glutamate
• D. Dopamine

Answer: (A)

Acetylcholine is the transmitter used by cholinergic neurons. When a signal reaches a cholinergic synapse, acetylcholine is released and then binds to receptors (nicotinic receptors at neuromuscular junctions and certain CNS synapses, or muscarinic receptors in other tissues). The signal is quickly terminated by acetylcholinesterase, which breaks down acetylcholine in the synaptic cleft. This transmitter is synthesized in the neuron by choline acetyltransferase from choline and acetyl-CoA. The cholinergic system underpins motor control at the neuromuscular junction, parasympathetic regulation of organ function, and various cognitive processes in the brain. By contrast, GABA is the main inhibitory transmitter in the CNS, glutamate is the primary excitatory neurotransmitter, and dopamine is involved in reward and movement modulation, not the defining signal of the cholinergic system.