Transport of CO2 (Carbon Dioxide) in the Blood
Neuron Action Potential Sequence of Events
- At rest, the axon membrane is slightly polarized to about -70mV, meaning the intracellular fluid (ICF) is relatively negative to the extracellular fluid (ECF).
- An action potential occurs when a portion of the membrane rapidly depolarizes and then repolarizes again to the original resting state.
- The process is initiated by a threshold level stimulus, such as a nearby change in membrane potential (threshold potential, local potential).
- At threhsold (about -55mV), many Na+ voltage-gated channels open.
- Na+ ions entering the cell make the membrane potential less negative. More Na+ channels open as result and a cycle of depolarization develops.
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- When the membrane potential reaches about +30mV (reverse polarization), the timed Na+ channels close due to inactivation and the Na+ influx stops.
- K+ voltage-gated channels open as Na+ channels close, in a delayed response to the original stimulus.
- K+ ions diffuse out of the cell and the efflux of positive charges causes the membrane to rapidly repolarize.
- The K+ channels are slow to close, so the membrane briefly hyperpolarizes.
- As the K+ channels close, Na+/K+ pumps actively transport Na+ ions out of the cell and K+ ions into the cell.
- The ion exchange helps re-establish the ion diffusion gradients and resting membrane potential.
- Lastly, the Na+ channels close (dein-activate) as the resting potential returns.