threshold of excitation

The ion conductances involved depend on the membrane potential and also the time after the membrane potential changes.[6]. [8] Typically in the axon or dendrite, there are small depolarizing or hyperpolarizing signals resulting from a prior stimulus. Also, ion concentration was shown to be the limiting factor in excitation. Depolarization | The phospholipid bilayer of the cell membrane is, in itself, highly impermeable to ions. the threshold of excitation. [17] These drugs, known as pro-arrhythmic agents, include antimicrobials, antipsychotics, methadone, and, ironically, antiarrhythmic agents. [12], A specific threshold tracking technique is threshold electrotonus, which uses the threshold tracking set-up to produce long-lasting subthreshold depolarizing or hyperpolarizing currents within a membrane. [3] If the influx of sodium ions fails to reach threshold, then sodium conductance does not increase a sufficient amount to override the resting potassium conductance. channels. [5] The larger the stimulus, the greater the depolarization, or attempt to reach threshold. This specific value of depolarization (in mV) is otherwise known as the threshold potential. This process can also be initiated by ligand or neurotransmitter binding to a ligand-gated channel. Initial experiments revolved around the concept that any electrical change that is brought about in neurons must occur through the action of ions. This material may not be reprinted or copied for any reason without the express written consent of AlleyDog.com. [12] Also, this technique allows for changes in threshold to be given a quantitative value, which when mathematically converted into a percentage, can be used to compare single fiber and multifiber preparations, different neuronal sites, and nerve excitability in different species. The excitation threshold refers to the level of neural depolarization that is necessary to generate an action potential. sodium ions (which are at greater concentration outside the neuron at This response has consistent characteristics regardless of the intensity of the initiating stimulus, as long as threshold is reached. [13], The most important factor determining threshold electrotonus is membrane potential, so threshold electrotonus can also be used as an index of membrane potential. The German physical chemist Walther Nernstapplied this concept in experiments to discover nervous excitability, and concluded that the local excitatory process through a semi-permeable membrane depends upon the ionic concentration. For example, ischemia and depolarization cause the same "fanning in" effect of the electrotonus waveforms. In a similar fashion, to appreciate how groups of cells work together in a meaningful way in the brain as a whole, we must first understand how individual cells in the brain function. A variety of drugs can present prolongation of the QT interval as a side effect.

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