Action Potential Differences In A Cell Membrane
At rest, a nerve cell maintains a difference in charge between the inside and the outside of the cell membrane. This difference in charge is continued by three factors. Firstly, in the cell membrane, there are sodium potassium ‘pumps’ crossing the membrane which are proteins that bring 2 potassium ions into the cell, for every 3 sodium ions it pumps out.
As well as this, there are protein channels which allow potassium ions in the cell to flow out via facilitated diffusion. Potassium diffuses out the cell much more readily than sodium diffuses in. Lastly there are many negatively charged organic anions such as some amino acids inside the cell. These three factors give rise the the difference in charge between the inside and the outside of …show more content…
The action potential is started when the membrane is very slightly ‘depolarised’, meaning that the charges inside and outside the cell become more similar. This happens when a stimulus causes a small influx of sodium ions into the cell. For an action potential to occur, the voltage has to pass a threshold value of -58mV. at this point, in a cycle of positive feedback, the action potential will always occur. Once the threshold value has been reached, it will cause voltage gated sodium channels to open allowing to diffuse into the cell down its electrochemical gradient. At this point the cells become much more depolarised. At the peak point of an action potential, the polarity inside the cell has shot up to +40mV. This temporary change in charge is the impulse. It moves down a neurone by local circuit currents which are created by the flow of ions. These currents cause just enough depolarisation for the next voltage gated sodium channel to be opened. It is useful to think of the system like dominoes. Once the first one is pushed, with only a small force, the rest will fall due to the previous one hitting it. This is why it is a positive feedback system. an all or nothing response occurs. This is why impulses can travel such long distances through nerves without slowing or
As well as this, there are protein channels which allow potassium ions in the cell to flow out via facilitated diffusion. Potassium diffuses out the cell much more readily than sodium diffuses in. Lastly there are many negatively charged organic anions such as some amino acids inside the cell. These three factors give rise the the difference in charge between the inside and the outside of …show more content…
The action potential is started when the membrane is very slightly ‘depolarised’, meaning that the charges inside and outside the cell become more similar. This happens when a stimulus causes a small influx of sodium ions into the cell. For an action potential to occur, the voltage has to pass a threshold value of -58mV. at this point, in a cycle of positive feedback, the action potential will always occur. Once the threshold value has been reached, it will cause voltage gated sodium channels to open allowing to diffuse into the cell down its electrochemical gradient. At this point the cells become much more depolarised. At the peak point of an action potential, the polarity inside the cell has shot up to +40mV. This temporary change in charge is the impulse. It moves down a neurone by local circuit currents which are created by the flow of ions. These currents cause just enough depolarisation for the next voltage gated sodium channel to be opened. It is useful to think of the system like dominoes. Once the first one is pushed, with only a small force, the rest will fall due to the previous one hitting it. This is why it is a positive feedback system. an all or nothing response occurs. This is why impulses can travel such long distances through nerves without slowing or