Peripheral nervous system, Action

CCK is found in the digestive tract and the central and peripheral nervous systems. In the brain, CCK coexists with DA. In the peripheral nervous system, the two principal physiological actions of CCK are stimulation of gaU. bladder contraction and pancreatic enzyme secretion. CCK also stimulates glucose and amino acid transport, protein and DNA synthesis, and pancreatic hormone secretion. In the CNS, CCK induces hypothermia, analgesia, hyperglycemia, stimulation of pituitary hormone release, and a decrease in exploratory behavior. The CCK family of neuropeptides has been impHcated in anxiety and panic disorders, psychoses, satiety, and gastric acid and pancreatic enzyme secretions. 

Agent BZ, 3-quinuchdinylbenzilate [6581 -06-2] C22H23NO2, is a typical incapacitant. BZ is one of a group of substances, many of them glycolate esters, sometimes known as atropinemimetics. Their action on the central and peripheral nervous systems resembles that of atropine [51-55-8] ... 

Page et al. (28) studied the activation threshold of pyrethrins for certain insects. This threshold point of toxicant in the insect occurred when the natural activity was replaced by forced activity caused by the action of the pyrethrins on the peripheral nervous system. 

The adrenergic system is an essential regulator that increases cardiovascular and metabolic capacity during situations ofstress, exercise, and disease. Nerve cells in the central and peripheral nervous system synthesize and secrete the neurotransmitters noradrenaline and adrenaline. In the peripheral nervous system, noradrenaline and adrenaline are released from two different sites noradrenaline is the principal neurotransmitter of sympathetic neurons that innervate many organs and tissues. In contrast, adrenaline, and to a lesser degree noradrenaline, is produced and secreted from the adrenal gland into the circulation (Fig. 1). Thus, the actions of noradrenaline are mostly restricted to the sites of release from sympathetic nerves, whereas adrenaline acts as a hormone to stimulate many different cells via the blood stream. 

The actions of all clinically used opiates can now be explained in terms of their acting as agonists at one of the four opiate receptors found in the brain, spinal cord and peripheral nervous system. All four receptors are inhibitory (Table 21.2). 

NGF also has actions within the CNS, although it is not particularly abundant in the CNS. Its synthesis appears to be largely restricted to the hippocampus and neocortex, and even in these regions it is present at relatively low concentrations relative to the other neurotrophins. The most prominent population of NGF-responsive neurons expressing TrkA are the basal forebrain cholinergic neurons. The principal projections of these neurons are to the hippocampus and cortex, which conforms with the concept that NGF acts as a target-derived trophic factor in the CNS, just as it does in the peripheral nervous system (PNS). NGF also acts on a subpopulation of cholinergic neurons within the striatum. These interneurons express the NGF receptor, TrkA, and respond to NGF. However, they do not appear to rely entirely on NGF for their survival, and the specific actions of NGF on this neuronal population have not been clearly defined. NGF may also have autocrine actions in the CNS, as some neuronal populations have been identified that express both TrkA and NGF. 

Anatomically, the nervous system is divided into the central nervous system (CNS) consisting of the brain and the spinal cord and the peripheral nervous system comprised of neural cells forming a network throughout the body. The peripheral system is itself subdivided into two sections the somatic system, where control of skeletal muscles allows movement and breathing, and the autonomic system which controls the actions of smooth muscle, cardiac muscle and glandular tissues. Further subdivision of the autonomic system based on anatomical and biochemical factors creates the sympathetic and parasympathetic nervous systems. 

Oligodendrocytes are present in the CNS as well and wrap around axons to form a myelin sheath. Myelin wraps into concentric layers that spiral around the axon. Gaps in the oligodendrocytes are the nodes of Ranvier, where the membrane maintains contact with extracellular fluid. The nodes serve to propagate the action potential in myelinated axons. Schwann cells perform an analogous function, myelinating axons in the peripheral nervous system. Not all neurons are myelinated, but myelination increases the metabolic efficiency of action potentials. Demyelination of neurons produces deficits in neuronal conduction, as is seen in multiple sclerosis. 

The fats also have a plastic function as they are included in cell membranes and other cell structures. The central and peripheral nervous systems are rich in lipids. PNFA are included in cell membranes, with their most significant function being the synthesis of cell hormones — prostaglandins. The properties of cell membranes as well as their interaction with external factors depend on the relation of PNFA concentration in cell components. In humans, prostaglandins are created not only in tissues but also in thrombocytes (thromboxanes) and in leucocytes (leukotrienes). The biological action of thrombocytes is extremely variant and depends on PNFA type which are the basis for fatty acid creation. 

Toxieology. Biphenyl is an irritant of the eyes and mucous membranes and may exert a toxic action on the central and peripheral nervous systems. 

The effects on sleep result from the psychostimulant and sympathomimetic actions of these drugs. They enhance noradrenergic, dopaminergic and serotonergic transmission in the central and peripheral nervous system mainly by increasing transmitter release and also inhibitory uptake. 

Other actions of kinins include activation of clotting factors simultaneously with the production of bradykinin. In the kidney, bradykinin production results in an increase in renal papillary blood flow, with a secondary inhibition of sodium reabsorption in the distal tubule. In the peripheral nervous system, bradykinin is important for the initiation of pain signals. It is also associated with the edema, erythema, and fever of inflammation. 

Mechanism of Action Competitive inhibitors of the muscarinic actions of acetylcholine, acting at receptors located in exocrine glands, smooth and cardiac muscle, and intramural neurons. Composed of 3 main constituents atropine, scopolamine, and hyoscyamine. Scopolamine exerts greater effects on the CNS, eye, and secretory glands than the constituents atropine and hyoscyamine. Atropine exerts more activity on the heart, intestine, and bronchial muscle and exhibits a more prolonged duration of action compared to scopolamine. Hyoscyamine exerts similar actions to atropine but has more potent central and peripheral nervous system effects. TherapeuticEffect Peripheral anticholinergic and antispasmodic action, mild sedation. Pharmacokinetics None known... 

Cholinesterase inhibitors have minimal effects by direct action on vascular smooth muscle because most vascular beds lack cholinergic innervation (coronary vasculature is an exception). At moderate doses, cholinesterase inhibitors cause an increase in systemic vascular resistance and blood pressure that is initiated at sympathetic ganglia in the case of quaternary nitrogen compounds and also at central sympathetic centers in the case of lipid-soluble agents. Atropine, acting in the central and peripheral nervous systems, can prevent the increase of blood pressure and the increased plasma norepinephrine. 

Endothelins interact with several endocrine systems, increasing the secretion of renin, aldosterone, vasopressin, and ANP. They exert a variety of actions on the central and peripheral nervous systems, the gastrointestinal system, the liver, the urinary tract, the male and female reproductive systems, the eye, the skeletal system, and the skin. Finally, ET-1 is a potent mitogen for vascular smooth muscle cells, cardiac myocytes, and glomerular mesangial cells. 

Diazinon toxicity results predominantly from the inhibition of acetylcholinesterase in the central and peripheral nervous system. The enzyme is responsible for terminating the action of the neurotransmitter, acetylcholine, in the synapse of the pre- and post-synaptic nerve endings or in the neuromuscular junction. However, the action of acetylcholine does not persist long as it is hydrolyzed by the enzyme, acetylcholinesterase, and rapidly removed. As an anticholinesterase organophosphate, diazinon inhibits acetylcholinesterase by reacting with the active site to form a stable phosphorylated complex which is incapable of destroying acetylcholine at the synaptic gutter between the pre- and post-synaptic nerve... 

We are discussing the peripheral nervous system at this point. Many of the NTs mentioned now wi appear in the section on the Central Nervous System but their modes of neuronal action may be very different. 

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