In everyday language, ”nervous” means ”anxious” or ”excitable,” and ”nerves” are what you’re a bundle of when you’re particularly anxious (not to be confused with “nerve,” which is what you have a lot of when you’re not anxious enough). Physiologically speaking, however, ”nervous” simply means ”having to do with nerves,” the parts of the body that specialize in transmitting information, You may have dissected a frog or a cat in a biology lab and isolated long stringy gray strands of tissue that were called nerves. These are really bundles of individual cells too small to be seen by the naked eye. Even under a microscope it is difficult to make out individual cells because their boundaries are so indistinct. In fact it wasn’t until 1875 that an Italian anatomist named Carrillo Golgi found a way to see the individual nerve cells. Golgi discovered that certain chemicals completely stained a small number of cells while leaving the rest completely unstained. The structure of the stained cells could then be clearly seen under a microscope. What Golgi saw were neurons, the basic message-carrying cells of the nervous system. The unstained cells were both nonneural cells and other neurons (only about 1 out of 100 neurons absorb the Golgi stain, for reasons that are still not completely understood).
A schematic diagram of a common type of neuron is shown in this article. Its major components are: the cell (which contains the nucleus of the cell), short limblike structures called dendrites extending from the cell body, and a longer thinner extension called an axon. (Actual neurons differ considerably in size. number of dendrites, and length of axon.). Through a process we will consider later neurons receive messages at the dendrite or cell body and relay them out along the axon to ocher neurons.
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