Nerve-cell membrane

The electrical signals are carried by the movement of charged ions across the cell membrane. This makes use of the potential energy stored across the cell membrane in the form of ionic gradients. Concentration gradients for the principal ions across a typical nerve cell membrane are indicated in Fig. 2.1(a). The cell interior has a high concentration of K+ ions and a low concentration of Na+, Cl and Ca + ions relative to the exterior. 

Figure 2.1 (a) Resting ionic gradients across a nerve cell membrane. Concentrations [ ] are in... 

Local anesthetics interact with peripheral nerve cell membranes and exert a pharmacological effect [34]. Potential oscillation was measured in the presence of 20 mM hydrochlorides of procaine, lidocaine, tetracaine, and dibucaine (structures shown in Fig. 16) [19]. Amplitude and the oscillatory and induction periods changed, the extent depending on the... 

In electrochemistry similar phenomena are observed, for example, with the formation of insoluble films on electrodes or with ion selective channel formation in bilayer lipid membranes or nerve cell membranes (pages 377 and 458). 

Mechanism of Action An antiparasiticagent that inhibits sodium influx through nerve cell membrane channels. Therapeutic Effect Results in delayed repolarization, paralysis, and death of parasites. 

Toxicity The acute oral LD50 and dermal LD50 toxicity of toxaphene in rats are 40 and 600 mg/kg, respectively. Toxaphene is an active nerve poison and interferes with fluxes of cations across nerve cell membranes, which increases neuronal irritability and results in convulsions and seizures. Toxaphene also has been found to damage the lungs, liver, and kidney of animals and humans. Although the dermal adsorption efficiency of toxaphene is less than that of other organochlorines, its absorption is enhanced by fat and fat solvents. Toxaphene has been shown to cause cancer in pregnant animals and to induce birth defects.68... 

The nerve cell membrane separates the external from the internal cell fluid, as does any cell membrane. As is true of virtually all cells, the intra- and extracellular fluids are electrolytic solutions of almost equal conductivity, but their chemical composition is very different. The ions present in largest quantities are sodium and potassium. The species in the external fluid are made up of more than 90 per cent sodium and chloride ions in the cell interior there are principally potassium and organic ions that cannot pass through the membrane, only 10 per cent of the ions being sodium and chloride. 

Fig. 17.3. (a) An action potential produced by a nerve-cell membrane in response to a depolarization (above the threshold) stimulus, (b) Sketch of time-dependent conductivity change of a nerve axon membrane (from Ref. 22... 

This is the essence of science. Even though I do not understand quantum mechanics or the nerve cell membrane, I trust those who do. Most scientists are quite ignorant about most sciences but all use a shared grammar that allows them to recognize their craft when they see it. The motto of the Royal Society of London is Nullius in verba trust not in words. Observation and experiment are what count, not opinion and introspection. Few working scientists have much respect for those who try to interpret nature in metaphysical terms. For most wearers of white coats, philosophy is to science as pornography is to sex it is cheaper, easier, and... 

Figure 4.6. Experimental evocation and detection of action potentials, a Detection of action potential propagation. Top Schematic of the experimental setup to trigger and detect action potential. Below Trace of an action potential passing the detection electrodes. The nnmbers refer to phases 1-4 as explained in the text b Local stimnlation, and the firing level. If a patch of nerve cell membrane is partially depolarized to a level of —55 mV, Na channels will start to open, and an all-out action potential will be triggered. In contrast, depolarizing stimuli that remain below the firing level will jnst dissipate, as will hyperpolarizing stimnli.

Chemical signaling (Na and K in nerve cell membranes, Ca " in cell budding Fe(II), Cu(I) and other metal ions ligating transmitters such as NO, aUcenes in, e.g. regulation of flowering, fruit formation by ethylene (produced by oxidative elimination from 1 -aminocyclopropane-1 -carboxylate (Habermehl et al. 2003 Mengel and Zickermann 2007)), allyl formate or similar compounds)... 

The chief toxic action of the organochlorine pesticides is on the nervous system, where these compounds interfere with fluxes of cations across nerve cell membranes, increasing neuronal irritability. This effect is manifest mainly as convulsions, sometimes limited to myoclonic jerking, but often... 

Figure 13.27. Selectivity of the Sodium Channel. The ionic selectivity of the sodium channel partly depends on steric factors. Sodium and lithium ions, together with a water molecule, fit in the channel, as do hydroxylamine and hydrazine. In contrast, K+ with a water molecule is too large. [After R. D. Keynes. Ion channels in the nerve-cell membrane. Copyright 1979 by Scientific American, Inc. All rights reserved.]...

Increased concentrations of methylmalonyl-CoA can lead to its rccojjnition by fatty acid synthase in place of maionyl-CoA. The use of this abnormal sub.strate leads to the production of branched-chain fatty acids. Here, the branch consists of a methyl group, deficiency induces the synthesis of very small amounts of methylated fatty acids. There is some thought that the odd-chain fatty acids and branched-chain fatty acids that increase in the deficiency, and become incorporated into nerve cells membranes, may contribute to the neurological problems associated with the deficiency. 

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