Nerves are the “telephone wiring” system that carries messages from the brain to the rest of the body. A nerve is like a telephone cable wrapped in insulation. An outer layer of tissue forms a cover to protect the nerve, just like the insulation surrounding a telephone cable (see Figure 1). A nerve contains millions of individual fibers grouped in bundles within the “insulated cable.”
Nerves serve as the “wires” of the body that carry information to and from the brain. Motor nerves carry messages from the brain to muscles to make the body move. Sensory nerves carry messages to the brain from different parts of the body to signal pain, pressure, and temperature. While the individual axon (nerve fiber) carries only one type of message, either motor or sensory, most nerves in the body are made up of both
Nerves are fragile and can be damaged by pressure, stretching, or cutting. Pressure or stretching injuries can cause the fibers carrying the information to break and stop the nerve from working, without disrupting the insulating cover. When a nerve is cut, both the nerve and the insulation are broken. Injury to a nerve can stop the transmission of signals to and from the brain, preventing muscles from working and causing loss of feeling in the area supplied by that nerve.
To fix a cut nerve, the insulation around both ends of the nerve is sewn together. A nerve in a finger is only as thick as a piece of thin spaghetti, so the stitches have to be very tiny and thin.The repair may need to be protected with a splint for the first 3 weeks to protect it from stretching apart since it is so delicate. The goal in fixing the nerve is to repair the outer cover so that nerve fibers can grow down the empty tubes to the muscles and sensory receptors and work again (see Figure 2). The surgeon tries to line up the ends of the nerve repair so that the fibers and empty tubes match up with each other as best as possible, but with millions of fibers in the nerve, not all of the original connections are likely to be re-established. If a wound is dirty or crushed, your physician may wait to fix the nerve until the skin has healed. If there is a gap between the ends of the nerve, the doctor may need to take a piece of nerve (nerve graft) from another part of the body to fix the injured nerve. This may cause permanent loss of feeling in the area where the nerve graft was taken. Smaller gaps can sometimes be bridged with “conduits” made from a vein or special cylinder.