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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.
Sympathetic nervous system stimulation causes vasoconstriction of most blood vessels, including many of those in the skin, the digestive tract, and the kidneys. This occurs due to the activation of alpha-1 adrenergic receptors by norepinephrine released by post-ganglionic sympathetic neurons.
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.
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.
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 ...
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 ...
The superior cervical ganglion (SCG) is the upper-most and largest [1] of the cervical sympathetic ganglia of the sympathetic trunk. [1] [2] It probably formed by the union of four sympathetic ganglia of the cervical spinal nerves C1–C4. [1] It is the only ganglion of the sympathetic nervous system that innervates the head and neck.
Group C fibers include postganglionic fibers in the autonomic nervous system (ANS), and nerve fibers at the dorsal roots (IV fiber). These fibers carry sensory information. Damage or injury to nerve fibers causes neuropathic pain. Capsaicin activates C fibre vanilloid receptors, providing the burning sensation associated with chili peppers.