Nerve Conduction: Within the Neuron

Modified: 2024-05-31

• 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.
• A good example of depolarization is a string of firecrackers.
  • If you watch them go off from a distance it looks like a continuous, moving explosion.
  • In actuality it is a series of individual firecrackers going off one after the other.
  • The same is true in the axon.
  • Each exchange of Na and K ions is akin to a tiny, local explosion.
• 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.