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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



(irritability), the ability of living cells, from the simplest unicellular organisms to the nerve cells of man, to sense environmental changes and to respond to these changes (stimuli) with excitation. Excitability is linked to the existence in the cell membrane of special molecular structures possessing specific sensitivity to various stimuli, such as electric current and chemical, mechanical, and thermal agents. Since the main component of excitation in nerve and muscle cells (fibers) is action potential, the excitability of these cells is usually judged by the threshold current strength or threshold shift in potential, which is sufficient for action potential to arise. The threshold current strength is depen-dent upon the duration of the stimulus. The threshold shift in potential, however, does not change with variation in the duration of the stimulus. The generation of action potential is based on increased permeability of the cell membrane to sodium ions. Accordingly, any agent that prevents the sodium permeability of a membrane from increasing causes excitability to decrease. Local anesthetics used in medicine, such as Novocain, cocaine, and dicaine, as well as various narcotics, such as ether barbiturates, are based on this mechanism.

The term “excitability” is also frequently used in medical and biological literature to characterize the state of the nerve centers in the brain and spinal cord, for example, the respiratory and vasomotor centers. In such cases excitability is judged by the lowest intensity of a stimulus that is required to elicit a reflex response.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
The purpose of this study was to examine acute effects of two types of stretching (SS and DS), isolated and in combination with specific basketball warm-up, on the neuromuscular excitability and vertical jump height in young basketball players.
We examined whether cathodal tDCS to SMA suppressed the abnormal excitability of SMA to reduce the activity of the CBG motor circuits, resulting in the inhibition of involuntary movements.
These results indicated that CIH could induce the LTF of genioglossus corticomotor activity, which occurs prior to the facilitation of the excitability of genioglossus muscle activity in rats.
We investigated CSE by measuring MEP amplitude evoked by TMS over M1 and spinal excitability by measuring H-reflex amplitude evoked by peripheral electrical nerve stimulation (PNS) over the posterior tibial nerve.
The Hmax/Mmax ratio (a measure of motor neuron excitability) was determined and analyzed.
This work demonstrated that EOLs and its main constituent thymol (percentage: ~66% of oil sample) are effective depressors of neuronal excitability. This effect was shown by the experimental analysis that quantified several electrophysiological parameters of sciatic nerve CAP, such as PPA, conduction velocity, rheobase and chronaxie.
Study co-author Stephen Jackson, the professor of cognitive neuroscience, the University of Nottingham, added: "If we can understand how alterations in cortical excitability give rise to neural disorders we can potentially reverse them."
[15] also showed improvements in paretic grip-lift performance accompanied by an immediate facilitation of ipsilesional M1 excitability after iTBS to the ipsilesional motor area.
"PEAK ATP is the only ingredient we know of that is proven to boost muscular excitability, a new and exciting category in sports nutrition.
The resting motor threshold is considered a global parameter of human brain excitability, as it is a compound measure of the membrane excitability of cortical motor neurons, neural inputs into pyramidal cells within the cortex, as well as the excitability of spinal motor neurons, neuromuscular junctions, and muscles [47, 48].
Further experiments in wild-type mice showed that experimental lowering of BRCA1 levels in the dentate gyrus caused neuronal dysfunction and shrinkage, as well as impairments in synaptic plasticity, excessive neuronal excitability, spatial learning and memory deficits, and increased DNA damage.
Spotlighting on translational biomarkers, Dr Koltzenberg will provide exclusive updates into nerve excitability profiling (NEP) and its use in studying ion, potassium and different subtypes of sodium channels in rodents and primates, including humans in vivo and in vitro.