Postganglionic nerve fibers
Sympathetic connections of the ciliary and superior cervical ganglia.
The neurotransmitters of postganglionic fibers differ:
- In the parasympathetic division, neurons are cholinergic (that is, acetylcholine is the primary neurotransmitter).
- In the sympathetic division, neurons are mostly adrenergic (that is, epinephrine and norepinephrine function as the primary neurotransmitters). Notable exceptions to this rule include the sympathetic innervation of sweat glands and arrectores pilorum muscles where the neurotransmitter at both pre and post ganglionic synapses is acetylcholine. Another notable structure is the medulla of the adrenal gland, where chromaffin cells function as modified post-ganglionic nerves. Instead of releasing epinephrine and norepinephrine into a synaptic cleft, cells of the adrenal medulla release these catecholamines into the blood stream as hormones. Like other components of the sympathetic nervous system, all of these exceptions are still stimulated by cholinergic pre ganglionic fibers.
- In both divisions of the autonomic nervous system, postganglionic neurons express nicotinic acetylcholine receptors to receive signals from preganglionic neurons.