Root canal therapy refers to the treatment of the inner aspects of a tooth, specifically that area inside a tooth originally occupied by the tooth's "pulp tissue".
Most people would probably refer to a tooth's pulp tissue as its "nerve". While a tooth's pulp tissue does contain nerve fibers it is also composed of arteries, veins, lymph vessels, and connective tissue.
Where precisely in a tooth is its nerve?
While teeth are hard calcified objects, they are not completely solid. In the inner most aspect of every tooth there lies a hollow space which, when a tooth is healthy, contains the tooth's nerve tissue. Dentists use the following terms to refer to various portions of this nerve area:
The pulp chamber.
This is a hollow space that lies more or less in the center of the tooth.
The root canals.
Each tooth's nerve enters the tooth, in generalities, at the tip of its root(s). From this point the nerve then runs through the center of the root in small "root canals" which subsequently join up with the tooth's pulp chamber.
What are the functions of a tooth's nerve tissue?
You might think that a tooth's nerve tissue is vitally important to a tooth's health and function, but in reality it's not. A tooth's nerve tissue plays an important role in the growth and development of the tooth, but once the tooth has erupted through the gums and has finished maturing the nerve's only function is sensory (it provides the tooth with the ability to feel hot and cold).
In regards to the normal day to day functioning of our mouths, the sensory information provided by a single tooth is really quite minimal. Dentists realize that on a practical level it is pretty much academic whether a tooth has a live nerve in it or not. If a tooth's nerve tissue is present and healthy, wonderful. But if a tooth has had its nerve tissue removed during root canal treatment that's fine too, you will never miss it.