Among the properties of the neuron is conductivity in all directions.
But when neurons are linked together it is found that nerve impulses will only pass from neuron A to neuron B, and not from neuron B to neuron A; that is, the transmission of the excited state or nervous impulse, although possible in each neuron both up and down its own cell branches, is possible from one nerve cell to another in one direction only.
In addition to the trophic influence exerted by each part of the neuron on its other parts, notably by the perikaryon on the cell branches, one neuron also in many instances influences the nutrition of other neurons.
Sleep is not exhaustion of the neuron in the sense that prolonged activity has reduced its excitability to zero.
This gentle continuous activity of the neuron is called its tonus.
This trophic influence which one neuron exerts upon others, or upon the cells of an extrinsic tissue, such as muscle, is exerted in that direction which is the one normally taken by the natural nerve impulses.
The wave of change (nervous impulse) induced in a neuron by advent of a stimulus is after all only a sudden augmentation of an activity continuous within the neuron - a transient accentuation of one (the disintegrative) phase of the metabolism inherent in and inseparable from its life.
The synapse, therefore, as the place of meeting of one neuron with the next is called, is said to valve the nerve circuits.
Each neuron or nerve cell is a morphologically distinct and discrete unit connected functionally but not structurally with its neighbours, and leading its own life independently of the destiny of its neighbours.
Any part of the cell cut off from the nucleus-containing part dies down: this is as true of nerve cells as of amoeba, and in regard to the neuron it constitutes what is known as the Wallerian degeneration.