Central nervous system

Central nervous system (CNS), system of nerve tissue in vertebrates that consists of the brain and spinal cord. Anatomically, the central nervous system (CNS) is centrally positioned along the midline axis of the body, where it is protected securely inside the skull and within the vertebral column, which is formed by successive vertebrae connected by dense ligaments. Functionally, the CNS serves a central role in receiving, processing, and coordinating responses to information from peripheral (outlying) sensory inputs. It helps regulate voluntary movements, such as those involved in walking and in speech, and involuntary movements, such as breathing and digesting food. Because it includes the brain, the CNS also is the center of emotion and cognition.

The CNS is one of the two main parts of the human nervous system, the other being the peripheral nervous system (PNS), which contains the neural tracts and structures outside of the brain and spinal cord. PNS pathways relay impulses carrying sensory signals to the CNS. Motor pathways transmit responses from the CNS to glands and muscles. In this capacity, the brain helps to plan and coordinate movement and oversees homeostasis, while the spinal cord provides a conduit for communication between the brain and peripheral structures. The spinal cord also contains neural circuits responsible for reflexes. These responses bypass the brain, allowing them to be instant and automatic.

The brain and spinal cord are surrounded by protective membranes known as the meninges, and both are cushioned by cerebrospinal fluid, a colorless liquid that circulates through the CNS. In addition, the brain and spinal cord contain both gray matter and white matter. The former is made up of large concentrations of neurons, including cell bodies, dendrites, and synapses (the junctions where two neurons meet). White matter, on the other hand, consists mainly of myelinated axons that are bundled together and that relay signals along tracts lying between different areas of the brain. Interconnected neural networks, which are formed by neurons and support cells known as glia, enable the CNS to receive and make sense of incoming signals.

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human nervous system: The central nervous system

See also nervous system.