Here is a picture of the living pulp tissue extending out from a broken tooth. This is the artery, vein & nerve which is what extends down the root of the tooth. This is what is removed during a root canal, also known as endodontic therapy.
The nerves [yellow] and blood vessels [blue and red] within the spongy bone of the jaw. The buccal plates are partially removed to show the path of the vessels and nerves into the teeth. Dentaltown Message Board Dental Anatomy and Tooth Morphology.