The neuron

The last of the four animal tissues, and the one built from the strangest cell in the body — a cell that can be more than a metre long.

Nervous tissue

Nervous tissue can be described as a very important tissue found in vertebrates. Its structural unit is the nerve cell, or neuron. Neurons are specialised for the transmission of impulses.

Figure to be added

Figure 1.21 — the structure of a typical neuron: a rounded cell body containing the nucleus, with many short branching dendrites spreading from one side of it, and a single long axon leaving the other side, wrapped in segments of myelin sheath with gaps between them, ending in a spray of small terminal branches.

Two main parts

Part	What it is
The cell body	Contains the nucleus, mitochondria, the Golgi complex, ribosomes and the endoplasmic reticulum — the same organelles as any other cell.
The processes	The extensions running out of the cell body. There are two kinds, and they run in opposite directions.
The axon	One process leaving the cell body. It carries impulses away from the cell body.
The dendrites	Short processes attached to the cell body. They receive stimuli and communicate them to the cell body.

One cell, and the impulse only goes one way through it

Dendrites in, cell body, axon out. That order is fixed, and it is what makes a nervous system able to carry information from somewhere to somewhere rather than simply buzzing. A neuron is a one-way street with a junction box in the middle.