Central Nervous System

The central nervous system (CNS) consists of a brain and spinal (nerve) cord. Most invertebrates and all vertebrates have sensory and motor neu­rons that are linked by way of a CNS. Most invertebrates have a CNS that is organized into a brain and a longitudinal nerve cord that is ventral to the digestive system, whereas chordates have a spinal cord that is hollow and dorsal to the digestive system. The CNS processes input from the internal and external environments, integrates information, and controls the body’s responses through efferent pathways to the body.

The brain is protected by the skull in vertebrates. The head is usually first to make contact with changes in the environment (for example, changes in light through the eyes, sound through the ears, and olfactory encounters through the nose), so it is beneficial to have the information-processing tis­sues of the nervous system concentrated there.

The nerve cord, or spinal cord, serves as a connection between the pe­ripheral nerves and the brain. It receives sensory information from the pe­riphery, relays it to the brain for interpretation and feedback, and coordinates many reflexes. It also contains the cell bodies of many of the neurons that control the body’s glandular and muscular responses by way of the periph­eral nervous system.

REFERNCES

Raven, Peter H., and George B. Johnson. Biology, 5th ed. Boston: McGraw-Hill, 1999.

Walker, Jr., Warren F., and Karel F. Liem. Functional Anatomy of the Vertebrates: An Evolutionary Perspective, 2nd ed. Orlando, FL: Saunders College Publishing,1994.