Resting Potential, Graded Potential, Action Potential - Computers ...

I have an exam coming up soon (Psychology), and I would really like to understand these concepts better. So to all those who have high knowledge regarding this topic, please read and inform me of any corrections or anything else I need to know. Note that I only need to understand what's necessary for a Psychology student to understand, so no need for overly technical terms and concepts, just the basics.

Here's how I understand it thus far:

A neuron is at a state of resting potential (potential for what?) when it isn't "firing" an impulse along its axon. At its resting potential, there tends to be more "negativity" inside the neuron than right outside of its membrane due to the presence of lots of positive ions (mainly Sodium ions) outside the membrane and the fact that negative ions inside are never allowed out. This is in spite of the presence of several positively charged Potassium (K+) ions that are inside. The measure of voltage across the membrane tends to be around -70 mV (I'd be grateful if someone could elaborate on this one). With this measure, it is said to be polarized (I also don't know what this means exactly).

That said, the neuron is not always at resting state and will quite often receive signals from neighboring cells that somehow stimulate the neuron's membrane to allow Sodium (Na+) ions to go through it into the cell. This causes a depolarization of the cell via reducing the negative difference in charge between the inside and the outside. Sometimes, however, the opposite occurs with the entrance of negative ions into the neuron or the exit of positive ions (mainly Potassium ions) to the outside, hyperpolarizing the cell via increasing the negative difference between the inside and outside. Whether it depolarizes or hyperpolarizes the neuron, the change in charge indicates a graded potential, and if enough depolarization occurs at various points of the neuron before the axon (and almost simultaneously), the tension to fire an impulse builds up and an action potential occurs (the threshold that needs to be crossed for this to happen is around -50 mV). Once it hits -50 mV, it will inevitably hit a positive difference of around +40 mV by the time it reaches the axon, and a firing occurs. This action potential is somehow interpreted as a firing (some elaboration here would be good as well).

Now in order to resolve the depolarization matter, what happens is that Potassium ions are forced out of the cell until the charge inside the neuron is back to -70 mV (it will actually go beyond -70 for a little while to compensate for the previous sudden increase in positivity but then restores itself to the default -70). And then the neuron is back to its resting state, but not before a message had already been sent to the next neurons or cells or whatever.

Any mistakes or incomplete information in what I said, let me know.

Source: http://www.wrongplanet.net/postt232959.html

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