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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.
There are two kinds of neurons involved in the transmission of any signal through the sympathetic system: pre-ganglionic and post-ganglionic. The shorter preganglionic neurons originate in the thoracolumbar division of the spinal cord specifically at T1 to L2~L3, and travel to a ganglion, often one of the paravertebral ganglia, where they synapse with a postganglionic neuron.
A preganglionic fibre may synapse to 15–20 postganglionic fibres. The postganglionic neurons extend across most of the body. [4] Upon exiting the sympathetic chain, the fibres enter a less-myelinated gray ramus communicans. There is still a myelin sheath present – but in far lower amounts compared to the white ramus communicans.
From here, the postganglionic sympathetic neuron can travel back out the grey ramus communicans of that level to the mixed spinal nerve and onto the effector organ. The preganglionic neuron can travel superiorly or inferiorly to a sympathetic paravertebral ganglion of a higher or lower level where it can synapse with a postganglionic ...
The SCG receives pre-ganglionic sympathetic afferents from the ciliospinal center which synapse in the ganglion. Post-ganglionic efferents then leave the SCG and join the internal carotid nerve plexus of the internal carotid artery, accompanying first this artery and subsequently its branches to reach the orbit and ultimately innervate the dilator pupillae muscle to mediate pupillary dilatation.
Most postganglionic sympathetic fibers are adrenergic: their neurotransmitter is norepinephrine except postganglionic sympathetic fibers to the sweat glands, piloerectile muscles of the body hairs, and the skeletal muscle arterioles do not use adrenaline/noradrenaline.
Electrical impulses carried by the sympathetic nervous system are converted to a chemical response in the adrenal gland. Chromaffin cells contained in the adrenal medulla act as postganglionic nerve fibers that release this chemical response into the blood as a circulating messenger. The sympathoadrenal system can activate and discharge ...
In the autonomic nervous system, there are both sympathetic and parasympathetic ganglia which contain the cell bodies of postganglionic sympathetic and parasympathetic neurons respectively. A pseudoganglion looks like a ganglion, but only has nerve fibers and has no nerve cell bodies.