Nervous System: Structure, Function, Evolution

Definition and overall role of nervous systems

The nervous system is the highly complex biological system that coordinates an animal’s actions and processes sensory information by transmitting signals to and from different body parts. It detects changes in the environment that affect the body and works together with the endocrine system to produce appropriate responses. In vertebrates, it is organized into two main divisions: the central nervous system (CNS), made up of the brain and spinal cord, and the peripheral nervous system (PNS), made up mainly of nerves that connect the CNS to the rest of the body. Overall, the nervous system enables communication through specialized cells—neurons—which send electrochemical signals along axons and communicate at synapses (electrical or chemical). Neurons can be excited, inhibited, or modulated by incoming signals, and their connections form neural pathways, circuits, and larger networks that shape perception and behavior. Alongside neurons, glial cells provide structural and metabolic support, help insulate axons via myelin, and contribute to immune and homeostatic functions, supporting the nervous system’s ability to function reliably. Functionally, the nervous system supports both rapid stimulus-response behaviors (such as reflexes) and more complex processing involving the brain and spinal cord. It can also generate activity patterns internally without external triggers, using mechanisms like central pattern generators and circadian rhythm control. Malfunction can arise from genetic defects, injury, toxins, infection, or aging, and disorders are studied and treated in neurology, while neuroscience focuses on studying nervous system function and organization.

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Central nervous system and peripheral nervous system

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