Reduced to lowest terms, the nervous system is found to be composed of minute units of structure called nerve-cells or neurones.

Some of the neurones are as long as three feet; others measure but a fraction of an inch in length.

It is important to note that neurones never act singly; they always act in groups, the nervous current passing from neurone to neurone.

It is important to note that neurones never act singly; they always act in groups, the nervous current passing from neurone to neurone.

It is thought that the most important changes in the nervous system do not occur within the individual neurones, but at the points where they join with each other.

This point of connection is called the synapse and although we do not understand its exact nature, it may well be pictured as a valve that governs the passage of the nervous current from neurone to neurone.

This point of connection is called the synapse and although we do not understand its exact nature, it may well be pictured as a valve that governs the passage of the nervous current from neurone to neurone.

With increased use they become more and more permeable, and thus learning is the process of making easier the passage of the nervous current from one neurone to another.

As soon as a neurone is stimulated at one end, it communicates its excitement, by means of the nervous current, to the next neurone or to neighboring neurones.

As soon as a neurone is stimulated at one end, it communicates its excitement, by means of the nervous current, to the next neurone or to neighboring neurones.

Just as an electric current might pass along one wire, thence to another, and along it to a third, so the nervous current passes from neurone to neurone.

In all these places we find ends of neurones which converge at the spinal cord and travel to the brain.

They are called sensory neurones and their function is to carry messages inward to the brain.

The area in the brain, where these neurones emerge, is near the top of the brain in the area marked Motor on the diagram.

The nerve-cells in this group are called motor neurones and their function is to carry messages from the brain out to the muscles, for a muscle ordinarily does not act without a nervous current to set it off.

They are called association neurones and transmit the nervous current from sensory areas to motor areas or from one sensory area to another.

The neural action accompanying this occurrence consists of an impression upon the nerve-cells in the eye, the conduction of the nervous current back to the visual area of the brain, the transmission of the current over association neurones to the motor area, then its transmission over the motor neurones, down the spinal cord, to the muscles that enable you to dodge the missile.

The neural action accompanying this occurrence consists of an impression upon the nerve-cells in the eye, the conduction of the nervous current back to the visual area of the brain, the transmission of the current over association neurones to the motor area, then its transmission over the motor neurones, down the spinal cord, to the muscles that enable you to dodge the missile.

The association neurones have the further function of connecting one sensory area in the brain with another.

For example, when you see, smell, taste and touch an orange, the corresponding areas in the brain act in conjunction and are associated by means of the association neurones connecting them.

The association neurones play a large part in the securing and organizing of knowledge.

Thence it pushes on, over association neurones in the brain to motor neurones, over which it passes down the spinal cord again to muscles, and ends in some movement.

Thence it pushes on, over association neurones in the brain to motor neurones, over which it passes down the spinal cord again to muscles, and ends in some movement.

The very structure and arrangement of the neurones is such that we are obliged to make some movement in response to objects affecting our sense organs.

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