The spinal cord, a thick rope of nervous tissue, is protected by a fluid-filled
bony canal and extends along the back. The spinal cord in an adult is roughly
18 inches long and ends just above the waistline. It serves not only as a
pathway for nerve signals to travel to and from the brain, but also as a
center for coordinating many reflex actions independently of the brain, like
jerking your hand away from something hot.