Chemical mediators in sympathetic and parasympathetic SNPA

In both sympathetic and parasympathetic SNPA ganglia, chemical synapses occur between the pre-ganglion and post-ganglion neurons.

In both cases, the neurotransmitter substance of the synapse is the acetylcholine.

In the terminations of postglandionary neurons, which synapse with the effector organs, however, the neurotransmitter substance is not the same for the two branches of SNPA. In parasympathetic SNPA the neurotransmitter is acetylcholine, as in ganglion synapses. In sympathetic SNPA, the neurotransmitter is, with few exceptions, the norepinephrine. One such exception is the postganglionic parasympathetic fiber that innervates the sweat glands, whose neurotransmitter is the acetylcholine.