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. The membrane potential is near the Nernst potential for the ion to which the membrane is primarily permeable - potassium!
Doubling of permeability does not mean that conductance exactly doubles. However, the relationship is not linear. Experimentally, we find that if the membrane channels for potassium are blocked by a chemical inhibitor, the action potential is prolonged! This page is Copyright,Thomas J. So, when the sodium conductance becomes very large relative to the other conductances, the membrane potential approaches the sodium Nernst potential, VNa 2.
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. Finally, notice that gK remains high for awhile. At rest 1the sodium conductance is very low relative to either potassium or chloride conductances.
During the initial phase of the action potential, potassium conductance, gK has been rising. 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.
For ions, which are charged particles, movement of mass and movement of electrical charge occur simulataneously. 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. High conductance indicates that electrical charge moves easily through a membrane.
So higher permeability indicates higher conductance. But, after initiation of the action potential, the sodium conductance rises very rapidly, quickly becoming much larger than either the potassium or chloride conductance.
High permeability indicates that particle mass moves easily through a membrane. Text, images, or Java applets may not be used for any commercial purpose or reprinted without the express written permission of Thomas J.
Herbert, University of Miami Before we begin 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.
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.
Conductance is the inverse of electrical resistance.Discuss the relative permeability of the membrane to Na+ and K+ in a resting neuron.
Your answer: The membrane is highly permeable to K+ because of the amount of K+ leak channels that are open. The membrane has a low permeability to Na+ ions because there are very few Na+ leak channels. 5. Discuss how a change in Na+ or K+ conductance would affect the resting membrane potential.
Your answer: A %(17). During resting potential, the inside of the axon is negative GRADED POTENTIAL ACTION POTENTIAL Action potential is a fleeting reversal of the membrane potential, caused by changes in permeability of the plasma membrane of neuron to potassium and sodium ions causing an electrical impulse to be transmitted along the axon.
Discuss how a change in Na+ or K+ conductance would affect the resting membrane potential. Your answer: Both are positively charged so when they move in and out of the cell the charge changes5/5(1).
Discuss how a change in Na+ or K+ conductance would affect the resting membrane potential. Your answer: The resting membrane potential depends on the intracellular and extracellular concentrations of the Na+ and K+ ions.
A change in the potassium conductance would have a greater effect on the resting membrane potential than a change in sodium would. Correct answer: a.
extracellular recordings of the action potential 3. An action potential is usually initiated in an axon at or near You correctly answered: d. all of the above 4. The initiation of an action potential in a sensory neuron in the body normally You correctly answered: a. follows a sufficiently large depolarizing receptor potential.Download