# Discuss how a change in na or k conductance would affect the resting membrane potential

Cell Membrane Potentials 1. So, the Nernst equation for either of these ions can be used to calculate the resting membrane potential. Herbert, University of Miami Before we begin High permeability indicates that particle mass moves easily through a membrane. High conductance indicates that electrical charge moves easily through a membrane.

Conductance is the inverse of electrical resistance. If the conductance of the membrane to a particular ion is low, then the resistance to movement of that ion across the membrane is high.

For ions, which are charged particles, movement of mass and movement of electrical charge occur simulataneously. So higher permeability indicates higher conductance.

However, the relationship is not linear. Doubling of permeability does not mean that conductance exactly doubles. In the following discussion, we look carefully at how each ion contributes to changes in membrane potential during an "action potential" by following what happens to sodium, potassium, and chloride conductances.

At rest 1the sodium conductance is very low relative to either potassium or chloride conductances. But, after initiation of the action potential, the sodium conductance rises very rapidly, quickly becoming much larger than either the potassium or chloride conductance.

Remember that membrane potential is determined by the relative conductances or permeabilities of the membrane to various ions, not the actual values of conductances or permeabilities.

## Basic Nomenclature

So, when the sodium conductance becomes very large relative to the other conductances, the membrane potential approaches the sodium Nernst potential, VNa 2. The membrane never quite reaches the actual sodium Nernst potential because of electrical capacitance - The sodium conductance is falling rapidly after its peak and the membrane potential never quite "catches up" to the conductance changes - There is a time lag between the two.

During the initial phase of the action potential, potassium conductance, gK has been rising. So, the increase in gK causes the action potential to decrease back towards the resting potential more rapidly than it would be expected to if gK did not change.

Experimentally, we find that if the membrane channels for potassium are blocked by a chemical inhibitor, the action potential is prolonged!

## Electrophysiology of Ventricular Action Potentials

Finally, notice that gK remains high for awhile. Since the potassium and chloride Nernst potentials are not quite the same - the potassium Nernst potential is somewhat lower than the resting potential - the effect of high gK, with gCl remaining constant, is to produce an "afterpotential" 4.

The membrane potential is near the Nernst potential for the ion to which the membrane is primarily permeable - potassium! This particular type of afterpotential is called a positive afterpotential because a long time ago, people used to make the recordings of membrane potential upside down - They didn't have intracellular electrodes and had to measure potentials with two electrodes on the outside of the cell - one near where the potential was changing and one some distance away where the potential was constant!

This page is Copyright,Thomas J. Text, images, or Java applets may not be used for any commercial purpose or reprinted without the express written permission of Thomas J.A Conductance on the Neuronal Input–Output Relationship: A Modeling Study is about 10 mV higher than the resting potential in mature mammalian neocortical pyramidal cells; thus GABAergic inputs could have fa-cilitatory, rather than inhibitory, effects on action potential generation.

The selective permeability of the membrane to K results in a resting potential (RP) that closely approximates the Nernst potential for K ions (E K) when [K] o is greater than ~3 mM. At lower K concentrations the relationship deviates from the Nernst relationship due . A Conductance on the Neuronal Input–Output Relationship: A Modeling Study is about 10 mV higher than the resting potential in mature mammalian neocortical pyramidal cells; thus GABAergic inputs could have fa-cilitatory, rather than inhibitory, effects on action potential generation. Figure illustrates the components of the membrane conductance, namely G Na and G K, and their sum G m during a propagating nerve impulse and the corresponding membrane voltage V m. This is a numerical solution of Equation (after Hodgkin and Huxley, d).

These conductances determine the subthreshold variations of the membrane potential V (t), according to the following membrane equation: where C denotes the membrane capacitance, I ext a stimulation current, G L the leak conductance, and E L the leak reversal potential, whereas E e and E i are the reversal potentials of g e (t) and g i (t.

A large gCl, carried by the ClC‐1 chloride channel, is important for muscle function as it stabilizes resting membrane potential (RMP) and helps to repolarize the membrane after action potentials (Aromataris and Rychkov, ).

K 1 and K 5 depend exponentially on membrane potential (V m) according to this relation: K(V m) = K(0)exp(zV m F/RT) where z is the equivalent gating charge, and F, R, and T are Faraday's constant, gas constant, and temperature, respectively.

Figure illustrates the components of the membrane conductance, namely G Na and G K, and their sum G m during a propagating nerve impulse and the corresponding membrane voltage V m.

This is a numerical solution of Equation (after Hodgkin and Huxley, d). Cell volume and resting transmembrane potential constitute two fundamental parameters of cell life. A cell contains inside its cytoplasm substances such as DNA, amino acids, ions such as K + or Na +, and sugar, which are essential to its srmvision.com synthetic process favors swelling of the cell (Lang et al.

), since the membrane permeability is very low.

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