Figure 2 shows a nerve cell. In fact there are many different types of nerve cells. The figure is only an illustration of what we may call a general nerve cell. Typically, a nerve cell is composed of:
- a cell body (soma)
- one long extension called an axon
- numerous short extensions called dendrites
Some nerve cells are surrounded by a structure called the myelin sheath (Fig. 2). This is coiled around the axon and insulates it. However, this is not a continuous structure. At intervals along the axon are small gaps in this insulation known as the Nodes of Ranvier. At its end an axon branches off and forms many axon terminals. The axon conveys the electrical nerve impulse generated in the soma, and this signal is transmitted to other nerve cells, muscles or glands via the axon terminals. The short dendrites also function to allow nerves cells to communicate with one another through propagation of electrical impulses from the soma.