Action potential

Action potential

1. 1. Resting

   • channels:
     • K+/Na+ pump leak channels
   • potential
     • sodium ions are carried outside while K+ is carried inside by the active transportation by the Na+/K+ pump in ratio of 3:2
       • K+ is leaked outside by the leak channels at a higher rate than the Na+ ions which result in a net negative influx to the inside
         • the membrane is imperiable to the negatively charge molecules including Cl- and proteins which are accumulated inside the cell
           • the resulting potential is thus negative to reach -90 in large nerves and -70 in small ones.

2. 2. Depolarization

   • in this stage, the Na+ ions are leaked inside the membrane.
     • potential rises due to this positive influx
       • if it reaches the threshold: the Action potential occurs and propagate along the nerve membrane to transfer the impulse
         • as the potential increases, voltage-gated sodium channels' activation and inactivation channels are activated as well as the potassium voltage-gated channels. however, they vary in how fast they respond
           • first the activation gate open to allow more Na+ to get in thus it reaches the maximum action potential
       • if it doesn't reach the threshold, Acute local potential occurs which is local potential in that specific site.
   • this period is considered the absolute refractory period at which, the nerve can't be re-excited upon any stimuli regardless its strenggth

3. 3. Repolarization

   • this stage occurs as the inactivation gate of the Na+ voltage-gated channels close to prevent any further influx of Na+ to the inside
     • then finally, the K+ voltage-gated channels open to allow a huge influx of K+ to outside, decreasing the potential again.
   • this stage is considered the relative refractory period

4. 4. Hyberrepolarization

   • due to the K+ influx to the outside and as it takes more tie than needed, the potential decreases even less that the resting potential to result in what is called hyperrepolarization

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