In a spinal anesthetic, a very thin needle is inserted between the bones of the lumbar spine, through the dura, and into the spinal canal, which is full of fluid. A small amount of local anesthetic is injected into the spinal fluid. This quickly stops the spinal nerves from working, so that there is no movement or sensation below that level of the body. The effect is temporary, lasting only until the local anesthetic wears off.
Different amounts and concentrations of local anesthetic allow anesthesiologists to control how high up the body the spinal block reaches and how long it lasts. This is also a very useful and safe way to provide anesthesia. The onset of spinal anesthesia is much quicker than with epidural anesthesia. Epidurals, however, are more flexible for providing analgesia for pain control, and at the same time allowing patients to be able to move quite freely.