The nervous system is the vast communication network that allows the body to sense, decide and act, and at its centre sits the brain, the most complex organ known. From the beat of the heart to the forming of a memory, almost everything a person does depends on signals passing through this network of specialised cells. Understanding its broad organisation gives a map for making sense of behaviour, feeling and thought.
The nervous system is usually divided into the central nervous system, the brain and spinal cord, and the peripheral nervous system, the nerves that reach the rest of the body. These parts work ceaselessly together, carrying information inward from the senses and outward to the muscles and glands, so that perception and action form a continuous loop rather than separate events.
Neurons and the Signals They Carry
The basic unit of the nervous system is the neuron, a cell specialised to receive, process and pass on signals. A neuron gathers inputs through branching extensions, and when these inputs are sufficient it sends an electrical impulse along a long fibre to its endings, where chemical messengers carry the signal across a tiny gap to the next cell. Billions of such cells, each connected to many others, form the networks from which all nervous activity arises.
The Central Nervous System
The central nervous system comprises the brain and the spinal cord, and it is where information is integrated and decisions are formed. The spinal cord relays signals between the body and the brain and governs some rapid reflexes on its own, while the brain carries out the higher work of perception, memory, emotion and planning. Protected by bone and fluid, the central nervous system is the hub to which the rest of the network connects.
The Peripheral Nervous System
Beyond the brain and spinal cord lies the peripheral nervous system, the nerves that carry information to and from the whole body. One division governs voluntary movement and the senses, while another, the autonomic division, quietly regulates the internal organs, balancing the systems that rouse the body for action against those that restore it to calm. Through these divisions the central nervous system reaches every muscle and organ.
Regions of the Brain and the Danger of Oversimplifying
The brain is often described in terms of regions associated with particular functions, from the deep structures that regulate basic drives and emotion to the outer cortex that supports perception, language and reasoning. Yet while such maps are useful, most real functions depend on many regions working together rather than on any single spot. Treating the brain as a set of isolated boxes oversimplifies a system whose power comes precisely from its dense interconnection.