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From the simple to the complex

Function by Level of Organization

Help Linked Module:  The Physical Factors Behind the Action Potential Linked Module:  Membrane Potential and Nerve Impulse Transmission Linked Module:  Membrane Potential and Action Potential

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.


Linked Module:  Animation on synaptic transmission (Please be patient while it downloads!)

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).

In addition to the chemical messengers and the receptors, the membrane channels play an essential role in each of these four phases of synaptic transmission.

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