Autonomic nervous system nicotine

Two distinct receptor groups have been identified for acetylcholine, the nicotinic and the muscarinic groups (Table 11.1). Furthermore, there are at least four subtypes of nicotinic and five subtypes of muscarinic receptors. Nicotinic receptors are ubiquitous and exist at the neuromuscular junctions of skeletal muscles and on ganglion cells in the autonomic nervous system. Nicotinic receptors located on cation-specific ion channels, when opened, evoke fast, transient depolarizations of the recipient cell. Muscarinic receptors are found in smooth muscle receiving parasympathetic innervation and elsewhere, and can be blocked by atropine. Muscarinic receptors are coupled indirectly to slow and fast ion channels via G proteins. 

Atropine, an alkaloid from Atropa belladonna, is the classical parasympatholytic compound. It competes with acetylcholine for the binding at the muscarinic receptor. Its affinity towards nicotinic receptors is very low, so that it does not interfere with the ganglionic transmission or the neuromotor transmission, at least in therapeutic dosages. However, in the central nervous system muscarinic receptor do play an important role and while atropine can penetrate the blood-brain barrier it exerts pronounced central effects. Atropine, like all other antagonists of the muscarinic acetylcholine receptor inhibit the stimulatory influence of the parasympathetic branch of the autonomous nervous system. All excretory glands (tear, sweat, salivary, gasto-intestinal, bronchi) are... 

The AChR in muscle is distinct from the AChRs found in the central and autonomic nervous systems (neuronal AChRs). Although both are activated by nicotine, each is blocked by a different antagonist (e.g., a-BTX vs. k-BTX). 

The answer is d. (Hardman, pp 192-193.) Nicotine is a depolarizing ganglionic blocking agent that initially stimulates and then blocks nicotinic muscular (NM) (skeletal muscle) and nicotinic neural (NN) (parasympathetic ganglia) cholinergic receptors. Blockade of the sympathetic division of the autonomic nervous system (ANS) results in arteriolar vasodilation, bradycardia, and hypotension. Blockade at the neuromuscu-... 

FIGURE 14.5 The autonomic nervous system innervates smooth muscle, cardiac muscles, and gland. ACh = acetylcholine N = nicotinic cholinergic receptors M = muscarinic cholinergic receptors S = sympathetic chain P = parasympathetic chain E = epinephrine D = dopamine NE = norepinephrine Sup. = superior Inf. = inferior. 

Actions Physostigmine has a wide range of actions because it stimulates not only muscarinic and nicotinic sites of the autonomic nervous system but also the nicotinic receptors of the neuromuscular junction. Its duration of action is about 2-4 hours. Physostigmine can enter and stimulate the CNS. 

Figure 7.6. Oiganisation of the autonomic nervous system, and the chemical types of synapses found within it. M Muscarinic, N Nicotinic cholinergic receptors D Dopaminergic, a, p Adrenergic receptors. (The irmervation of skeletal muscles by a-mo-toneurons is shown for comparison but not part of the autonomic system.) BBB Blood brain barrier. It protects the entire central nervous system, i.e. both the brain and the spinal cord.

As we have seen [in a previous chapter], acetylcholine occurs in s niapses in both the somatic and the autonomic nervous system. The nicotinic acetylcholine receptor is found in the motor endplate of the skeletal muscle, and in both the sympathetic and the parasympathetic ganglia of the peripheral autonomic system. Muscarinic acetylcholine receptors are found at the endings of all secondary neurons within the parasympathetic part of the peripheral autonomous system. In addition, acetylcholine receptors of both types also occur in the brain. Drugs with a useful degree of selectivity for each of these targets are available and used in practical medicine. Selectivity is based on two principles ... 

Tobacco smoke includes 4000 chemical species with varying potential which cause adverse effects. Nicotine is stimulating to the autonomic nervous system ganglia and neuromuscular junction. The most prominent effects relate to stimulation of the adrenal medulla, central nervous system (CNS), cardiovascular system (release of catecholamines), gastrointestinal tract (parasympathetic stimulation), salivary and bronchial glands, and the medullary vomiting center. There is subsequent blockade of autonomic ganglia and the neuromuscular junction transmission, inhibition of catecholamine release from the adrenal medulla, and CNS depression. 

Symptoms No exposure sympathetic autonomic nervous system predominance Muscarinic predomi- nance Nicotinic predominance No exposure antimusca-rinic predomi- nance... 

For example, the nicotinic receptor for ACh (present in autonomic nervous system [ANS] ganglia, the skeletal myoneural junction, and the central nervous system [CNS]) is coupled to a Na+/K+ ion channel. The receptor is a target for many drugs, including nicotine, choline esters, ganglion blockers, and skeletal muscle relaxants. 

Nicotinic-cholinergic receptors that are part of the autonomic nervous system may be stimulated at low concentrations of nicotine, but blocked at higher concentrations. The repeated use of nicotine-containing products (which includes chewing tobacco, chewing nicotine-containing gum, or the use of therapeutic patches that release nicotine for skin absorption) promotes the formation of (new) nicotinic-cholinergic receptors. The tolerance... 

The autonomic nervous system (ANS) consists of parasympathetic and sympathetic neurons. The transmitter for the parasympathetic system is acetylcholine (ACh), which acts on muscarinic and nicotinic cholinergic receptors. Muscarinic receptors are located on effector organs and mediate typical parasympathetic responses, such as. salivation, /acrimation, urination, and c/efecation (SLUD), as well as various cardiovascular responses. Prototypical muscarinic actions are ... 

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