Ganglia autonomic nervous system

Muscarinic effects, mediated by acetylcholine, the primary transmitter of the autonomic nervous system ganglia, are inhibited by the anticholinergic effects exerted by antihistamines. Anticholinergic side effects include dry mouth, urinary retention, blurred vision, and constipation. Because first-generation antihistamines also distribute into the CNS, sedation is a prominent side effect. The development of second-generation antihistamines, such as loratadine and fexofenadine, lack anticholinergic activity and do not distribute into the CNS (Table 31-1). Hence, they are not typically associated with sedation and do not possess antiemetic properties. 

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. 

Autonomic ganglia. Ganglionic stimulation occurs in both the sympathetic and parasympathetic divisions of the autonomic nervous system. Parasympathetic activation results in increased production of gastric juice (smoking ban in peptic ulcer) and enhanced bowel motility ( laxative effect of the first morning cigarette defecation diarrhea in the novice). 

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... 

Anatomical differences between the peripheral somatic and autonomic nervous systems have led to their classification as separate divisions of the nervous system. These differences are shown in Figure 9.1. The axon of a somatic motor neuron leaves the CNS and travels without interruption to the innervated effector cell. In contrast, two neurons are required to connect the CNS and a visceral effector cell of the autonomic nervous system. The first neuron in this sequence is called the preganglionic neuron. The second neuron, whose cell body is within the ganglion, travels to the visceral effector cell it is called the postganglionic neuron. 

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-... 

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. 

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. 

Synapses of the autonomic nervous system are vulnerable to poisoning by botulinum neurotoxins (Dickson and Shevky, 1923). One of the most frequently used preparation is the superior cervical ganglion (Eccles and Libet, 1961 Mochida efal., 1995). 

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. 

Ganglionic transmission Acetylcholine transmits both sympathetic and parasympathetic impulses from the "preganglionic" neurons in the brain and spinal cord to nicotinic ganglionic (N ) receptors on "postganglionic" neurons of the autonomic nervous system. This occurs in sympathetic ganglia, which are located along the spinal cord, and in parasympa-... 

Acetylcholine is stored in storage vesicles. 3). Upon nerve stimulation, an action potential travels down the neuron and causes calcium influx into the nerve terminal. Calcium influx causes the vesicles to fuse with plasma membrane and release acetylcholine. Acetylcholine diffuses through the synaptic cleft and may bind to (4) Nm receptors (nicotinic receptors on muscle cells, (5) Ng receptors (nicotinic receptors on ganglionic synapses of the autonomic nervous system), (6) Ml muscarinic receptors, (7) M2 muscarinic receptors or (8) M3 muscarinic receptors. At least six muscarinic receptors have now been identified, of which Ml, M2 and M3 receptors have been most carefully studied (Table 2.5). 

This type of analysis demonstrates the predominant effect of cholinesterase inhibition by these compounds in the autonomic nervous system of the dog to be manifest at post-ganglionic parasympathetic nerve-endings. 

Fig. 7.3 summarizes the anatomical features of the autonomic nervous system. This differs from the voluntary system (exemplified by the neuro-niuscular junction in Fig. 7.1) in that one extra control point exists for each fibre, namely an extra synapse (situated in a ganglion). In sympathetic fibres, these ganglia are not far from the spinal cord in parasympathetic fibres, the ganglia are near the end-organ, i.e. the one which the nerve is to influence. As... 

Histologic changes similar to those of the brain are found in the spinal cord and in the ganglion cells of the autonomous nervous system. 

The parasynqtathetic system is also known as the craniosacral portion of the autonomic nervous system because of the sites of origin of the pre-ganglionic fibers. The cranial portion has ganglia associated with the third, seventh, ninth, and tenth cranial nerves. Spinal cord segments S2, S3, and S4 comprise the sacral portion. 

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