Nervous System
The nervous system is the organ system that coordinates voluntary and involuntary actions and transmits signals between different parts of the body using a network of neurons. In vertebrates it is divided into the central nervous system (CNS), comprising the brain and spinal cord, and the peripheral nervous system (PNS), comprising all neural tissue outside the CNS. The nervous system integrates sensory information, processes it, and generates appropriate motor or physiological responses, making it central to behavior, cognition, and homeostasis.
Divisions of the Human Nervous System
| Division | Components | Primary Function | Example Response |
|---|---|---|---|
| Central Nervous System (CNS) | Brain, spinal cord | Integration and processing | Interpreting pain signals |
| Peripheral Nervous System (PNS) | Cranial and spinal nerves | Signal relay | Sending motor commands to muscles |
| Somatic PNS | Sensory and motor neurons | Voluntary movement and sensation | Lifting a cup |
| Autonomic – Sympathetic | Thoracolumbar nerves | Fight-or-flight response | Increased heart rate under stress |
| Autonomic – Parasympathetic | Craniosacral nerves | Rest and digest | Slowing heart rate after rest |
| Enteric | Gut wall neurons | GI tract regulation | Peristalsis |
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Related Terms
Neuron
A neuron is the fundamental structural and functional unit of the nervous system, specialized for receiving, processing, and transmitting electrochemical signals. Each neuron consists of a cell body (soma), dendrites that receive incoming signals, and an axon that transmits signals away to other neurons, muscles, or glands. The human brain contains approximately 86 billion neurons, and the precise connectivity and signaling between them underlies all cognitive processes, sensory perception, and motor control.
Synapse
A synapse is the specialized junction between two neurons, or between a neuron and a target cell such as a muscle or gland, across which nerve impulses are transmitted via chemical neurotransmitters or direct electrical coupling. In a chemical synapse, an action potential in the presynaptic neuron triggers the release of neurotransmitters from synaptic vesicles into the synaptic cleft, where they bind to receptors on the postsynaptic membrane and alter its excitability. Synaptic strength can be modified through processes of long-term potentiation (LTP) and long-term depression (LTD), which are thought to underlie learning and memory.
Homeostasis
Homeostasis is the tendency of biological systems to maintain relatively stable internal conditions despite changes in the external environment, achieved through a series of regulatory feedback mechanisms. It operates primarily through negative feedback loops in which deviations from a set point trigger corrective responses to restore equilibrium. Maintaining homeostasis is essential for survival, as critical variables such as body temperature (37°C in humans), blood glucose (70–100 mg/dL), and blood pH (7.35–7.45) must be kept within narrow physiological ranges.
From Latin "nervosus" (sinewy, vigorous) and "systema" from Greek "systema" (organized whole). The systematic study of the nervous system began with ancient Greeks including Hippocrates and Galen, though modern neuroscience emerged in the 19th century with Santiago Ramón y Cajal.