Describe the structure and functions of the human spinal cord.

Concepts to Consider: The human brain and spinal cord are protected by bone and three layers of connective tissue, collectively known as the meninges: the dura mater, arachnoid, and pia mater. The brain and spinal cord are cushioned by cerebrospinal fluid (CSF). The spinal cord transmits impulses to and from the brain and control s many reflex actions. The spinal cord consists of ascending tracts, which transmit information to the brain, and descending tracts, which transmit information from the brain. Its gray matter contains nuclei that serve as reflex centers. A withdrawal reflex involves sensory receptors; sensory neurons, interneurons, and motor neurons; and effectors, such as muscles.