Nerve Conduction: Within the Neuron
In the vast majority of animals, including humans, nerve conduction
is an electro-chemical process. It is electric within the neuron and
chemical between neurons. Within the neuron it is the process of
depolarization that makes it electrical. Note that it is not much
electricity; the charge difference is about -70 millivolts. What does
depolarization mean? Think of a car battery; it has two poles. One is
labelled (+) and one is labelled (-). That battery is polarized; you
can depolarize it (do not do this, you will be sorry) by connecting a
wire to each pole and touching them together. Sparks will fly, and
electricity will flow. When the neuron is at rest, when it is not
conducting a nerve impulse or action potential, it is polarized. That
polarization is accomplished by the separation of sodium (Na) and
potassium (K) ions by the neuron's cell membrane. The action
potential consists of the invasion of the cell by the Na ions and the
simultaneous expulsion of the K ions. So the electric charge
difference is momentarily gone. This process continues down the axon
so that the effect is like a wave of depolarization.
When the depolarization reaches the terminal buttons, it causes
neurotransmitters to be released into the synapse. Those
neurotransmitters either excite or inhibit the post-synaptic neuron.
If they excite it, then the action potential will continue on the
post-synaptic neuron. If they inhibit it, then the action potential
will stop.
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