Autonomic nervous system neurotransmission

The concept of chemical neurotransmission originated in the 1920s with the classic experiments of Otto Loewi (which were themselves inspired by a dream), who demonstrated that by transferring the ventricular fluid of a stimulated frog heart onto an unstimulated frog heart he could reproduce the effects of a (parasympathetic) nerve stimulus on the unstimulated heart (Loewi Navratil, 1926). Subsequently, it was found that acetylcholine was the neurotransmitter released from these parasympathetic nerve fibers. As well as playing a critical role in synaptic transmission in the autonomic nervous system and at vertebrate neuromuscular junctions (Dale, 1935), acetylcholine plays a central role in the control of wakefulness and REM sleep. Some have even gone as far as to call acetylcholine a neurotransmitter correlate of consciousness (Perry et al., 1999). 

Muscarinic receptors are responsible for postganglionic parasympathetic neurotransmission and thus for control of a wide range of smooth muscle, cardiac muscle and secretory responses. Some responses originating in the sympathetic division of the autonomic nervous system, such as sweating and piloerection, also are mediated through muscarinic receptors. 

Beside this there are some major differences with the neurotransmission in the autonomous nervous system The contractile activity of the skeletal muscle is almost completely dependent on the innervation. There is no basal tone and a loss of the innervation is identical to a total loss in function of the particular skeletal muscle. In contrast to the target organs of the parasympathetic nervous system the skeletal muscle cells only have acetylcholine receptors at the site of the so-called end-plate, the connection between neuron and muscle cell with the rest of the cell surface being insensitive to the transmitter. The release of acetylcholine results in a postjunctional depolarization which is either above the threshold to induce an action potential and a contraction or below the threshold with no contractile response at all. In contrast to the graduated reactions of the parasympathetic target organs, this is an all or nothing transmission. 

Neurotransmission in the autonomic nervous system is an example of the more general process of chemical signaling between cells. In addition to neurotransmission, other types of chemical signaling are the release of local mediators and the secretion of hormones. 

Q6 How may anticholinesterases affect neurotransmission within the autonomic nervous system ... 

Hoffrnan B, Taylor P. Neurotransmission. The autonomic nervous system. In Linmbird L, ed. The Pharmacologic Basis of Therapeutics, Vol. New York McGraw-Hill, 2001 115-53. 

Colchicine disrupts the movement of secretory vesicles within a cell, and thus interferes with chemical neurotransmission. If administered quickly or in elevatEd dose, the drug interferes with homeostatic mechanisms, particularly those mediated by the autonomic nervous system. Inhibition of medullary regulation of respiration, decreased thalamic control of core temperature, as well as inhibition of peripheral vasodilatation, leading to hypertension, may be seen. 

Thousands of neuronal signals race through our brains each moment, controlling our breathing, movements, thoughts and emotions with admirable precision. Neuronal circuits provide the basic "road map" for brain signals, and chemical neurotransmitters carry information from one neuron to another. Neurotransmission in the brain parallels that in the autonomic nervous system (Chapter 2), but utilizes several chemicals and peptides in addition to acetylcholine and norepinephrine. Neurotransmitters that have been most carefully studied are introduced below. 

Wood, J. D. (1999) Neurotransmission at the interface of sympathetic and enteric divisions of autonomic nervous system. Clin J. Physiol. 42, 201-10. 

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. 

Lefkowitz RJ, Hoffman BB, Taylor P. 1996. Neurotransmission The autonomic and somatic motor nervous systems. In Hardman JG, Limbird EE, eds. Goodman Gilman s the pharmacological basis of therapeutics. New York, NY McGraw-Hill, 105-139. 

Hoffman, B.B., Lefkowitz, R.J., and Taylor, P., Neurotransmission the autonomic and somatic motor nervous systems, in Goodman and Gilman s The Pharmacological Basis of Therapeutics, 9th ed., Hardman, J.G. and Limbird, L.E., Eds., McGraw-Hill, New York, 1996, chap. 6. 

For almost one century, acetylcholine has been recognized as a neurotransmitter both in the central nervous system and the peripheral nervous system. In the peripheral nervous system, acetylcholine has been identified as the neurotransmitter of autonomic ganglia and the neuromuscular junction. Acetylcholine is involved in different peripheral functions such as heart rate, blood flow, gastrointestinal tract motility, and sweat production and smooth muscle activity. In the CNS, cholinergic neurotransmission plays a crucial role in a variety of CNS functions including sensory perception, motor function, cognitive processing, memory, arousal, attention, sleep, nociception, motivation, reward, mood, and psychosis. 

Nicotiana tabacum, and lobeline, present in the dried leaves and tops of the herb, Lobelia inflata (13). Both nicotine and lobeline act as agonists on a specific type of acetylcholine receptor, the nicotinic cholinergic receptor. In mammals, nicotinic cholinergic receptors mediate cholinergic neurotransmission in skeletal muscles, autonomic ganglia, and the central nervous system. At these sites nicotine s action has two phases, excitation and depression. Insect central nervous tissues are rich in nicotinic cholinergic receptors (cf. 14), but their role in behavior is not well understood. 

NEUROTRANSMISSION THE AUTONOMIC AND SOMATIC MOTOR NERVOUS SYSTEMS... 

CHAPTER 6 Neurotransmission The Autonomic and Somatic Motor Nervous Systems 87... 

The nicotinic acetylcholine (ACh) receptor mediates neurotransmission postsynaptically at the neuromuscular junction and peripheral autonomic ganglia in the central nervous system (CNS), it largely controls release of neurotransmitters from presynaptic sites. The receptor is called the nicotinic acetylcholine receptor because it is stimulated by both the neurotransmitter ACh and the alkaloid nicotine. 

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