Reference guide · Updated 04 October 2026
A connected system for sensing, deciding, and responding
The nervous system receives information, processes it, and coordinates responses throughout the body. It supports sensation, movement, automatic processes, learning, memory, and many other everyday functions.
The nervous system can be understood as a communication network. Receptors detect changes inside or outside the body, nerves carry signals, and the brain and spinal cord help interpret information and organise a response.
Its two broad divisions are the central nervous system, made up of the brain and spinal cord, and the peripheral nervous system, made up of nerves and ganglia outside the brain and spinal cord.
Main Functions of the Nervous System
These activities overlap. A single experience, such as touching a warm surface, can involve sensory detection, rapid protection, movement, and later learning.
Sensory function gathers information through receptors for touch, pressure, temperature, light, sound, smell, taste, and body position. Sensory pathways carry much of this information towards the central nervous system.
Motor function sends instructions to muscles and glands. Some movements are chosen consciously, while others are coordinated automatically to maintain posture, breathing, circulation, and other essential processes.
Integration allows incoming information to be compared, interpreted, and connected with memory or context. The resulting response may be immediate, deliberate, or largely automatic.
Divisions of the Nervous System
The divisions of the nervous system describe connected groups with different roles. They are not isolated systems: information continually travels between them.
Cranial nerves
Cranial nerves connect the brain with structures in the head and neck. They contribute to smell, sight, hearing, balance, facial movement, swallowing, and other sensory or motor functions. Humans have twelve pairs of cranial nerves.
Peripheral nervous system
The peripheral nervous system includes nerves and ganglia outside the brain and spinal cord. It links the central nervous system with the skin, muscles, joints, glands, and internal organs. Spinal nerves branch from the spinal cord and distribute signals throughout the body.
Autonomic nervous system
The autonomic nervous system helps regulate functions that usually occur without conscious effort, including heart rate, digestion, breathing patterns, pupil size, and blood-vessel activity. Its sympathetic and parasympathetic branches often work in complementary ways.
Central nervous system
The central nervous system consists of the brain and spinal cord. It receives and organises information, supports thought and memory, and coordinates many voluntary and involuntary responses.
Building Blocks of the Nervous System
The nervous system is built from nerve cells and supporting cells. Neurons transmit electrical and chemical signals. Glial cells support neurons, help maintain their environment, contribute to insulation, and participate in repair and protection.
Neuron anatomy
A typical neuron has several specialised parts:
- Cell body: contains the nucleus and maintains the cell.
- Dendrites: receive signals from other cells.
- Axon: carries an electrical signal away from the cell body.
- Myelin: an insulating layer around many axons.
- Nodes: gaps between myelin segments that help signals travel efficiently.
- Axon terminals: release chemical messengers at connections called synapses.
Types of neurons
Neurons can be grouped by shape, direction of information flow, or job. Sensory neurons carry information towards the central nervous system. Motor neurons carry instructions towards muscles or glands. Interneurons connect neurons within the brain and spinal cord and help form processing networks.
Structural classifications include unipolar, bipolar, pseudounipolar, and multipolar neurons. These names describe how processes extend from the cell body; they do not by themselves explain the entire function of a neuron.
The Central Nervous System
The brain and spinal cord form the central processing core. The brain includes the cerebrum, cerebellum, and brainstem, while the spinal cord provides a major route for signals travelling between the brain and the rest of the body.
| Structure | Broad role |
|---|---|
| Cerebrum | Thought, perception, language, memory, and voluntary action |
| Cerebellum | Coordination, balance, and movement refinement |
| Brainstem | Connections and essential automatic functions |
| Spinal cord | Signal routes and rapid protective reflexes |
Protective tissues and fluid surround the central nervous system. These structures help cushion the brain and spinal cord and create a carefully regulated environment for nerve cells.
The Peripheral Nervous System
The peripheral nervous system carries information between the central nervous system and the body. Its sensory pathways report changes such as pressure or temperature, while its motor pathways help produce movement and regulate organs.
A reflex can be organised through the spinal cord before the brain has fully processed the event. The brain can then receive information about what happened and adjust the response or store it as useful experience.
References and further reading
This educational overview is intended to introduce terminology rather than provide medical advice. Continue with related Brain Made Simple guides: