(It is the body's major neural tract, a thin, tubular bundle of nerves that is enclosed in and protected by the bony vertebral column. Injury to the spinal cord may result in a loss of communication between the brain and sections of the spinal cord, causing paralysis, loss of sensation, or weakness in parts of the body. According to Biological Psychology, 6th Edition, 1998, the human spinal cord contains around 1 billion neurons.)