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

Images and files in the map