“Eccrine glands are innervated by the sympathetic nervous system (SNS), primarily by cholinergic fibers whose discharge is altered primarily by changes in deep body temperature (core temperature), but by adrenergic fibers as well. The glands on palms and soles do not respond to temperature but secrete at times of emotional stress.”
Because they are innervated by the SNS, they are part of the fight or flight response system. “Their innervation consists of two parts, a preganglionic and postganglionic neuron. The preganglionic neuron is short, originates from the thoracolumbar region of the spinal cord, uses acetylcholine as its neurotransmitter, and synapses with the postganglionic neuron via a nicotinic acetylcholine. The postganglionic neuron for sweat gland innervation differs from other sympathetic postganglionic neurons in that it releases acetylcholine to act on muscarinic receptors; all other sympathetic postganglionic neurons, with the exception of the adrenal medulla, use norepinephrine.” Open anesthesia
There are 3 types of sweat glands in humans, eccrine, apocrine, and apoeccrine glands. Eccrine sweat glands are the main glands responsible for hyperhidrosis
Eccrine sweat glands are found all over the body, but they occur in the highest density in the palms, soles. A small amount is found in the axillae.
Thermal vs. Emotional (stress) related sweating
“Sweating on the face, chest, and back is generally due to heat stimuli, while sweating of the palms and soles is due to emotional stress. The axillae have eccrine, apocrine, and apoeccrine glands.
Thermal sweating can occur throughout the day, but emotional sweating (palms, soles, and to some degree axillae) stops while sleeping.
Eccrine glands are innervated by the SNS but utilize acetylcholine as the primary neurotransmitter. Thermal sweating and emotional sweating are controlled by different regions of the brain. Thermal sweating is controlled by the hypothalamus via the thermosensitive preoptic sweat center, while emotional sweating is regulated by the cerebral cortex.
A sympathetic signal is carried to endocrine glands via cholinergic autonomic neurons. In patients with primary focal hyperhidrosis, the sweat glands are usually histologically and functionally normal. Rather, the cause of hyperhidrosis appears to be an abnormal or exaggerated central response to normal emotional stress.” Uptodate.com
Generalized hyperhidrosis may be due to systemic diseases or medications. “Unlike primary focal hyperhidrosis, patients with generalized, secondary hyperhidrosis usually present as adults and report sweating that occurs both while awake and sleeping.”
Control of Sweating
- Thermal control – integration between internal and skin temperatures
- Non-thermal factors: 1) Exercise; 2) Baroreceptor loading state, and 3) Body fluid status
Further reading
Shibasaki M, Crandall CG. Mechanisms and controllers of eccrine sweating in humans. Frontiers in bioscience (Scholar edition). 2010;2:685-696. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2866164/
Neuroscience. 2008 Oct 2; 156(2): 310–318. Sweat Gland Innervation is pioneered by Sympathetic Neurons Expressing a cholinergic/noradrenergic co-phenotype in mouse. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2689353/
www.openanesthesia.org/sweat_glands_innervation
www.uptodate.com/contents/primary-focal-hyperhidrosis