Sweat glands sympathetic innervation

Organs receiving only sympathetic innervation Although most tissues receive dual innervation, some effector organs, such as the adrenal medulla, kidney, pilomotor muscles, and sweat glands, receive innervation only from the sympathetic system. The control of blood pressure is also mainly a sympathetic activity, with essentially no participation by the parasympathetic system. 

Qi Sweat glands are innervated by the sympathetic division of the autonomic nervous system. The postganglionic transmitter is, however, acetylcholine. 

Figure 9.2 Autonomic nerve pathways. All preganglionic neurons release acetylcholine (Ach), which binds to nicotinic receptors (N) on the postganglionic neurons. All postganglionic neurons in the parasympathetic system and some sympathetic postganglionic neurons innervating sweat glands release Ach that binds to muscarinic (M) receptors on the cells of the effector tissue. The remaining postganglionic neurons of the sympathetic system release norepinephrine (NE), which binds to alpha (a) or beta (P) receptors on cells of the effector tissue. The cells of the adrenal medulla, which are modified postganglionic neurons in the sympathetic system, release epinephrine (EPI) and NE into the circulation.

Sweat glands are also innervated by sympathetic fibers (wet palms due to excitement) however, these are exceptional as regards their neurotransmitter (ACh, p. 106). 

Atropine suppresses thermoregulatory sweating. Sympathetic cholinergic fibers innervate eccrine sweat glands, and their muscarinic receptors are readily accessible to antimuscarinic drugs. In adults, body temperature is elevated by this effect only if large doses are administered, but in infants and children even ordinary doses may cause "atropine fever."... 

Sweat glands have sympathetic cholinergic innervation. Patients with cystic fibrosis secrete a large amount of salt in their sweat and this forms the basis of a diagnostic test for the condition. 

Q4 The ganglionic transmitter of both divisions of the autonomic nervous system is acetylcholine. The major postganglionic neurotransmitter of the sympathetic nervous system is norepinephrine (noradrenaline), but a small number of structures are innervated by sympathetic, cholinergic fibres. These fibres release acetylcholine and the structures innervated include the sweat glands and blood vessels supplying skeletal muscle. In the parasympathetic system the postganglionic neurotransmitter is acetylcholine. 

Sweating is stimulated by direct action of the increased endogenous acetylcholine on muscarinic receptors of sweat glands in the skin these glands are innervated by the sympathetic division of the autonomic nervous system. Agitation is produced by a central excitatory effect on cholinergic neurones in the brain, but in large doses anticholinesterases can cause depression of the respiratory centre in the medulla. 

Muscarinic acetylcholine receptors occur in the target tissues. They are mostly found in parasympathetic s mapses, but they also occur in the sympathetically innervated sweat glands. 

Exocrine glands. All secretions except milk are diminished. Dry mouth and dry eye are common. Gastric acid secretion is reduced but so also is the total volume of gastric secretion so that pH may be little altered. Sweating is inhibited (sympathetic innervation but releasing acetylcholine). Bronchial secretions are reduced and may become viscid, which can be a disadvantage, as removal of secretion by cough and ciliary action is rendered less effective. 

BZ is a competitive inhibitor of muscarinic receptors associated with the parasympathetic nervous system that innervate the eyes, heart, respiratory system, skin, gastrointestinal tract, and bladder. The sweat glands, innervated by the sympathetic nervous system, are also modulated by muscarinic receptors. By any route of exposure, the onset of action is approximately 1 h, with peak effects occurring 8h postexposure. Signs and symptoms gradually subside over 2-4 days. Most of the absorbed BZ is excreted via the kidney. 

Postganglionic sympathetic fibers innervating sweat glands are cholinergic hence, muscarine also causes sweating. 

Other factors have been described which influence the transmitter phenotype of the sympathetic neurons. Most of the sympathetic neurons are adrenergic, except for those which innervate the sweat glands, which are cholinergic. One of the factors which may influence the switching of phenotype of these neurons to cholinergic has recently been purified and is equivalent to LIF (Yamamori et al., 1989). As discussed below, it is beginning to emerge that LIF has multiple activities within the nervous system as well as outside it. 

Schotzinger, R.J. and Landis, S.C. (1990) Acquisition of cholinergic and peptidergic properties by sympathetic innervation of rat sweat glands requires interaction with normal target. Neuron 5 91-100. 

Leblanc, G. and Landis, S. (1986) Development of choline acetyltransferase (CAT) in the sympathetic innervation of rat sweat glands. J. Neurosci. 6 260-265. 

Small doses of atropine or scopolamine inhibit the activity of sweat glands innervated by sympathetic cholinergic fibers, making the skin hot and dry. After large doses or at high environmental... 

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