None of our perceptions, thoughts, or memories would be possible
without nerve conduction, the process by which nerve impulses are
propagated along our neurons.
Nerve conduction is an electrochemical
process, which means that it uses electricity made with chemical
molecules. In other words, the electricity in the brain is not
produced by electrons flowing the way they do through a household
electrical wire. Instead, the brain’s electricity is caused by the movements of electrically
charged molecules through the neurons’ membranes.
The membrane of a neuron, like that of any other cell, contains
tiny holes known as channels. It is through these channels that
charged molecules pass through the neural membrane.
But unlike the channels in other cells, the
channels in neurons are so specialized that they can coordinate
the movements of these charges across the membrane so as to conduct
nerve impulses. The following diagram shows in simplified form
the sequence of events by which a nerve impulse is conducted (click
on step numbers 2 and 3 to see the corresponding steps).
Scientists know a great deal about the charged molecules that
generate nerve impulses and the sequence
of their movements.
But conduction of a nerve impulse down a
single neuron would serve no purpose were it not for the other
major component of neuronal
communication: the synaptic
transmission that lets the impulse pass from one neuron to
the next.
The brain’s great computational
abilities are derived from the communication
among its billions of nerve cells. But the process of neural
conduction that lets a nerve impulse
propagate down a neuron would serve no purpose if it were not coupled
with another mechanism: the synaptic transmission that lets the
impulse pass from one neuron to the next.
At the synapse
between two neurons, they do not actually touch each other.
They therefore need to secrete chemical
messengers that travel from one neuron to the other to regenerate
the nerve impulse.
This mechanism of synaptic transmission can be divided into four
main steps. (Click on step numbers 2, 3, and 4 in the diagram below
to see the corresponding steps).
