A-type current absolute refractory period afterhyperpolarization (mV)

amplitude (mV)

A transient outward K+ current that activates and inactivates rapidly. A-type currents are coded for by the Kv4 potassium channel gene subfamily. In addition, Kv1.4 and other Kv1 proteins can form A-type currents when complexed with accessory cytoplasmic proteins (e.g., ,5-subunits). A-type currents contribute to the resting potential, participate in repetitive firing and spike repolarization, and prevent back-propagation of dendritic APs.

The time interval during which a second AP cannot be elicited, regardless of stimuli intensity. A temporal slow hyperpolariza-tion observed after a train of APs. Often plays a role in the regulation of the neuron's firing rate. Property of an AP that refers to the mV difference between the RMP and peak.

anode break excitation conductance delayed rectifier depolarization duration (ms)

hyperpolarization (mV)

Generation of an AP at the end of a long-duration depolarization or hyperpolarizing pulse.

Property of a channel that characterizes its ability to conduct current.

Outward K+ currents that activate slowly (delayed with respect to activation of voltage-gated sodium current). These channels show little, if any, inactivation in the range of seconds. These channels play a predominant role in AP repolarization.

Change that results in a more positive (less negative) MP. A measure of the time that depolarization lasts during an AP (e.g., interval between threshold on the rising phase and recovering half of the AP amplitude on the falling phase). Change that results in a more negative (less positive) MP.

inactivation inward rectifier ionic dependence outward rectifier peak (mV) permeability potassium current (IK) rate of fall (mV ms~1)

rectifier refractory period (ms)

A process that leads to a nonconducting channel state that does not respond to depolarization by opening of the channel. Also known as anomalous rectifiers (as opposed to normal outward rectification), these potassium channels pass inward currents at potentials more negative than the K+ equilibrium potential of (EK). The Kir subfamily of voltage-gated ion channels (VGICs) codes for inward rectifiers. Inward rectifiers are strongly regulated by intracellular factors and second messengers and contribute to maintenance of the resting potential and K+ homeostasis.

Property of an AP that refers to the principal ion driving the depolarization.

A channel that allows current to flow in an outward direction more easily than an inward direction.

The voltage at which the maximum AP amplitude is reached. Ion channel property that determines the rate at which ions pass through the pore. Ion flux through a potassium-selective ion channel. Change in MP per unit time during the falling (repolarizing) phase of the AP. Used as an indirect measure of potassium current density.

Change in MP per time unit during the rising (depolarizing) phase of the AP. Used as an indirect measure of sodium current density.

In electronics, a circuit that converts bidirectional current (AC) to unidirectional current (DC). In physiology, a nonlinear I/V relationship produced when a membrane conductance is dependent upon the direction of traffic of the permeant ion. As a result, a rectifying current preferentially flows in one direction and not the other. A primary determinant of the maximal rate of firing of a relative refractory period repolarization rheobase (nA)

sodium current (INa) threshold (mV)

The briefest interval after which a second AP can be elicited, albeit with diminished amplitude.

Change that brings the MP back towards the resting value. The minimum amount of current needed to generate at least one AP.

Ion flux through a sodium-selective ion channel. The minimum value of the MP at which an AP is initiated. Threshold can also be defined as the absolute depolarization magnitude from the RP required to initiate an AP.

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