Expert: Walter Hintz - 11/3/2007

Question
For the life of me I cannot figure out the deal with action potential and the whole depolarization, repolarization and the whole process. Can u please explain in clear english what the purpose of the proces is for in the muscles and nervous system and how it works?  I've been confused for 3 weeks on this please help.

Answer
Hello giovanna
It is not as complicated as it looks. It is difficult for me to explain it without making sketches but I will try. Your comprehension depends upon what you already know about cell biology.
 Visualize an axon of a neuron.  The function of the cell is to transmit an impulse to generate an action. As you know the cellular cytoplasm is contained by the cell membrane.  The cytoplasm contains negative ions and the extracellular fluids have an abundance of sodium ions   (+ions).  The cell membrane is polarized when there is a buildup of Na ions on the outside of the cell and negative ions inside.  An action potential is established because the  + ions are attracted to the - ions but the + ions(sodium) cannot enter the because the membrane is impermeable to them.  When the nerve is stimulated by neurotransmitters the membrane becomes permeable and sodium enters the cell  in a  depolarizing wave.  At the end of the axon the impulse causes  the release of transmitters at the synapse that stimulate the next nerve cell.  The impulse eventually brings about an motor response like a muscle contraction.
The depolarizing wave is immediately followed by a repolarization wave when sodium is pumped out of the cytoplasm by active transport and the action potential creates the situation for the next impulse.
 There are other ions involved like Potassium and bicarbonate ions.
I you have any problems with this explanation let me know.