hi in this video I'm going to talk about voltage gated ion channels so these are the channels which change the membrane potential and thus allow an action potential so here are the channels the white channels are the voltage gated sodium channels and the black are voltage gated potassium channels here are all the charges sitting on each side of the membrane this membrane is currently at its resting membrane potential which has been set up by an sodium pottassium atpa which is not shown here see the previous tutorial for an explanation of how the sodium potassium ATP as sets up this resting membrane po potential so this is the outside of the cell or the extra cellular environment and this is the inside of the cell or intracellular remember in the last tutorial we said that sodium wanted to move this way but couldn't and potassium the other way well they still can't because their channels are closed however if we change the voltage across the membrane by adding positive charges here and here then this gate flips open on the sodium Channel and this allows sodium to flow into the cell down its concentration gradient this means there is an influx of positively charged sodium ions and the positive charges start lining up across the membrane with the Nega charges lining up on the other side so this is a reversal of the resting membrane potential now remember that we also applied a positive charge to the voltage gated potassium Channel well this also flips open but there is a delay before this happens but when it does happen the pottassium rushes out removing positive charges from the cell and placing them on the other side side of the membrane and this Returns the membrane potential back toward the resting membrane potential these channels are both open at the moment so they need to be closed the sodium channels close about the same time the potassium channels open and they close by this ball and chain method this ball gets stuck in the channel and sodium can't flow through anymore after a delay the potassium channels also close now potassium can't flow and this keeps the membrane potential back near the resting membrane potential so if we look at a voltage recording taken inside the cell and we look at voltage versus time then we start with our resting membrane potential then we applied our stimulus and this opened the voltage gated sodium channels the cells become more positive and we can see that on this graph now here the potassium channels open and the sodium channels close the positively charged potassium rushes out of the cell and the cell becomes more negatively charged and we can see that drop on this graph also then the potassium Channel close and the resting membrane potential returns this up and down graph shows a typical action potential in the next video we will look at how Action potentials propagate along a membrane such as an axon for more free tutorials and the PDF for this tutorial visit www.h handwritten tutorial.com