The central nervous system (CNS) is the division of the nervous system consisting of the brain and spinal cord. It processes information about the body and its surroundings, coordinates responses, and supports perception, thought, memory, and behavior. Together with the peripheral nervous system, it connects sensory input with motor output and regulates many involuntary bodily activities. The account below primarily describes the human CNS. (nichd.nih.gov)
Anatomical organization
The brain occupies the cranial cavity, while the spinal cord lies within the vertebral canal. The adult brain has four major anatomical regions: the cerebrum, diencephalon, brainstem, and cerebellum. These regions contain interconnected circuits rather than functioning as independent control centers. (openstax.org)
The cerebrum consists of two hemispheres. Its folded outer layer, the cerebral cortex, participates in sensory processing, voluntary movement, and higher cognitive functions. Beneath it lie white matter and groups of neurons called nuclei. The corpus callosum is a major white-matter pathway connecting the cerebral hemispheres. The diencephalon includes the thalamus, which processes and relays information, and the hypothalamus, which regulates homeostasis through autonomic and endocrine mechanisms. (openstax.org)
The brainstem comprises the midbrain, pons, and medulla. It connects the brain with the spinal cord and contains pathways and nuclei involved in sensory processing, movement, breathing, and cardiovascular regulation. The cerebellum, attached to the brainstem, contributes to movement coordination and learned motor performance. (openstax.org)
The spinal cord contains ascending pathways carrying information toward the brain and descending pathways carrying commands toward spinal circuits. It also integrates sensory input locally, contributing to reflexes and coordinated movement. Its posterior regions primarily receive sensory information, whereas anterior regions contain neurons associated with motor output. (ninds.nih.gov)
Cells and tissue organization
The principal signaling cells are neurons. A typical neuron has a cell body, receiving processes called dendrites, and an axon that carries signals toward other cells. Neurons communicate through specialized junctions called synapses. At chemical synapses, neurotransmitters released from one cell influence the activity of another. Communication across networks of neurons underlies the coordinated functions of the CNS. (nichd.nih.gov)
Glial cells support neural tissue in several ways, including maintaining the local chemical environment, regulating neurotransmitters, providing structural support, and removing damaged cellular material. Some glia form myelin, an insulating sheath around axons that helps nerve impulses travel efficiently. Glia are therefore active participants in nervous-system function, not simply material filling spaces between neurons. (nichd.nih.gov)
The CNS contains both gray matter and white matter. Gray matter includes concentrations of neuronal cell bodies and their local connections; white matter contains bundles of axons linking different regions. In the cerebrum, gray matter forms the cortex and deeper nuclei. In the spinal cord, a central region of gray matter is surrounded by white matter, producing a characteristic butterfly-like pattern in cross section. (openstax.org)
Protection and internal environment
The skull and vertebral column provide mechanical protection. Three membranes, collectively called the meninges, surround the brain and spinal cord: the outer dura mater, middle arachnoid mater, and inner pia mater. The pia closely follows the surface of nervous tissue, while the space beneath the arachnoid contains cerebrospinal fluid (CSF). (ncbi.nlm.nih.gov)
CSF circulates through the brain’s ventricles and around the CNS. It cushions nervous tissue and participates in the movement of metabolic waste. Its circulation connects internal fluid spaces with pathways through which fluid returns to the wider circulation. (openstax.org)
The blood–brain barrier regulates exchange between circulating blood and the brain’s extracellular environment. Tight junctions between specialized capillary endothelial cells restrict passage between cells, while transport mechanisms control the movement of many substances across them. Supporting cells and surrounding structures help maintain this barrier. It is selective rather than absolute and contributes to the stable environment required for neural signaling. A distinct blood–CSF barrier operates at the choroid plexuses. (ncbi.nlm.nih.gov)
Functional integration
CNS activity links information about external stimuli and internal bodily conditions with appropriate responses. Sensory pathways convey information relevant to vision, hearing, touch, and other senses. Motor systems influence skeletal muscles, while central autonomic circuits participate in regulating involuntary functions such as heart rate and digestion. (nichd.nih.gov)
Thinking, emotions, and behavior arise through communication among multiple neural networks. Although particular regions have identifiable roles, complex activities depend on cooperation across regions. The same broad anatomical system therefore supports both conscious experiences and essential processes that occur without conscious attention. (nichd.nih.gov)
Development
Early in embryonic development, the neural tube forms the precursor of the brain and spinal cord. Its cranial portion develops into the brain, while the remaining portion gives rise to the spinal cord. Incomplete closure can produce congenital abnormalities affecting these structures. (nichd.nih.gov)
Developing neurons migrate, acquire specialized characteristics, and establish connections with other cells. Their position, shape, and signaling properties depend partly on developmental signals from neighboring cells. These processes assemble the circuits that subsequently support sensory, motor, and cognitive functions. (ninds.nih.gov)
Disorders and investigation
CNS disorders include vascular conditions such as stroke, traumatic injuries, infections, developmental abnormalities, degenerative diseases, seizure disorders, and tumors. Their effects depend on the structures involved and the nature and extent of damage. Spinal cord injury, for example, can impair sensation, movement, and autonomic regulation below the affected level. (ninds.nih.gov)
Clinical investigation combines history and neurological examination with selected tests. Examinations assess functions such as sensation, movement, coordination, balance, language, and memory. Magnetic resonance imaging, other imaging methods, and blood or CSF analysis provide complementary information about nervous-system structure and disease processes. (ninds.nih.gov)