ACTION POTENTIAL

ACTION POTENTIAL

1. it happens in places where it is necessary to conduct electric energy - for example, neurons and muscle cells

   • intracellular medium ► K + ► predominate negative electric charges
   • Extracellular medium ► NaCl ► positive electric charges predominate

2. When excited, the inversion of the polarity (happens very fast) / depolarization will occur, which is when the Action Potential happens

3. For depolarization to occur, Na + must enter this cell to increase the positive charge of the cell. Depolarization is the inversion of charges. This inversion takes place through the entrance of Na +.

4. Variation of the membrane potential at rest = -90mV ► to trigger the action potential, the Na + enters slowly, the internal environment becomes more and more positive.

   • There will come a time that is called the 'threshold potential', abrupt reversal of polarity.
     • This inversion is called the 'all or nothing' effect.
       • That's when depolarization happens.
         • On this occasion, voltage-activated ion channels are activated. As the internal environment becomes more and more positive this electric charge increasingly positive activates the voltage-dependent ion channels (-70mV). They activate everything at once, so the abrupt rise.
           • When the membrane potential variation becomes positive, inversion of the characteristics of the extra medium and the intracellular environment occurs.
             • The intracellular medium becomes positive and the extra cellular medium becomes negative
               • There will come a time when the Na + stops from entering and the dependent voltage ion channels will be closed. They are also closed by varying the electrical condition of the cell - when the inside of the cell is around 35mV a modification occurs in the channels, but now to close.
                 • As soon as channels close, with 35mV, then K + channels open
                   • K + is more concentrated on the inside than on the outside. It has a positive charge.
                     • Then, once you get out, it will leave the inner environment more negative. Then, in repolarization, the potassium channels are activated voltage dependent (allows the K + of the intra cellular environment). The voltage decreases, but goes from -90mV, which is a hyperpolarization.
                       • K + channels are activated at approximately 35mV. However, they close around -95mV, which is called late closing of the channels of k +
                       • the Potassium Sodium Pump throws the outside K + into the intracellular medium and Na + that is inside throws out, both with energy expenditure, this to rebalance the ions that have been exchanged to unleash the Potential for action.
                         • When it reaches equilibrium, return to basal conditions, this is the resting potential. If you want to trigger a new PA, initiate the process, which lasts approximately 8 ms. o Refractory periods - cell can not or has difficulty to depolarize. Absolute refractory period (1 of image) In this condition, you can not trigger another PA. You need to complete one to start another. o In hyperpolarization (2 of the image), relative refractory period. It would take much more Na + than in the rest position Who maintains the electrical balance of the cells is the sodium potassium pump. Myelinic neurons travel the PA faster than those without the Myelin Sheath - jumping impulse between the myelin sheaths, which are the nodes of Ranvier

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