Autonomic ganglia, cholinergic

In addition to the cholinergic and adrenergic receptors on autonomic ganglion cells, there also appear to be receptors for a variety of excitatory and inhibitory substances, including angiotensin, bradykinin, histamine, 5-hydroxytryptaimine (serotonin), and substance P. The... 

Neurotransmission at both cholinergic and adrenergic synapses can be influenced by a variety of naturally occurring and synthetic drugs (Table 38.2). For example, ACh secretion is drastically reduced in the presence of botulinum toxin which contains proteases that cleave proteins vital to the process of exocytosis. Nicotine, one of the active ingredients in tobacco can mimic the effects of ACh and increase (or decrease at high doses) autonomic ganglionic transmission as well as that at the... 

Treatment of cholinergic symptoms by autonomic ganglionic blockade would be undesirable in that the effect of such treatment is to abolish sympathetic as well as parasympathetic tone. Removal of sympathetic tone adds to the existing bradycardia and hypotension which form part of the syndrome of intoxication by cholinesterase inhibitors. 

Cholinergic neurotransmission ChEs terminate cholinergic transmission in the central nervous system (CNS), in NMJs and in the autonomic system (the parasympathetic system, somatic motor nerves and pre-ganglionic sympathetic nerves). A few sensory cells and the NMJ in nematodes also include ChEs. 

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-... 

Schematic diagram comparing some anatomic and neurotransmitter features of autonomic and somatic motor nerves. Only the primary transmitter substances are shown. Parasympathetic ganglia are not shown because most are in or near the wall of the organ innervated. Cholinergic nerves are shown in blue noradrenergic in red and dopaminergic in green. Note that some sympathetic postganglionic fibers release acetylcholine or dopamine rather than norepinephrine. The adrenal medulla, a modified sympathetic ganglion, receives sympathetic preganglionic fibers and releases epinephrine and norepinephrine into the blood. ACh, acetylcholine D, dopamine Epi, epinephrine M, muscarinic receptors N, nicotinic receptors NE, norepinephrine.

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. 

The primary pathway of cholinergic transmission in autonomic ganglia is similar to that at the neuromuscular junction of skeletal muscle. The initial depolarization is the result of activation of nicotinic ACh receptors, which are ligand-gated cation channels with properties similar to those found at the neuromuscular junction. Several secondary transmitters or modulators either enhance or diminish the sensitivity of the postganglionic cell to ACh. Ganglionic transmission is discussed in more detail in Chapter 9. 

The cholinergic synapses in autonomic ganglia are more complex Each ganglionic cell has many synaptic inputs. The receptors on the postsynaptic membrane differ qualitatively. The ChR principally responsible for the transmission is of the nicotinic type (N-ChR). In addition, there are receptors of muscarinic type (M-ChR see p. 242). 

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