nervous system: Quick Facts

Written and fact-checked by

The Information Architects of Encyclopaedia Britannica

Last updated

Oct. 27, 2026

News •

Crows can evaluate visual info twice as fast as mammals • Oct. 23, 2026, 1:32 PM ET (Ars Technica)

Is the brain actually 2 nervous systems smooshed together? A new study claims it is. • Oct. 17, 2026, 7:00 AM ET (Live Science)

Photos and Videos

Diagram comparing action potential conduction in myelinated and unmyelinated axons, showing a neuron with labeled cell body, myelin sheath, nodes of Ranvier, and the flow of electrical signals along each type of axon.

Diagram comparing the nervous systems of a flatworm (Planaria) and a grasshopper, showing labeled nerve cords, nerve clusters, and nerves in both organisms, with the brain indicated in each.

Diagram of a Hydra, a cnidarian, showing its simple nervous system as a network of interconnected nerves called a nerve net spread throughout its body and tentacles.

Illustration showing the side view of a cat's head with its brain highlighted, alongside a labeled diagram of the cat brain identifying the olfactory bulb, cerebrum, and cerebellum.

Diagram of a neuron showing the cell body with nucleus, branching dendrites, a long axon covered by myelin sheaths from Schwann cells, and nodes of Ranvier. Labels identify the nerve impulse path, axon terminals, and synapses, with an inset highlighting the myelin sheath and node structure.

neuron from visual cortex of a rat

Two U-shaped tubes illustrate water diffusion across a semipermeable membrane. In diagram A, water moves from side 1 to side 2, driven by osmotic pressure and a concentration gradient, with impermeant substances unable to cross the membrane. In diagram B, hydrostatic pressure opposes the movement. Key concepts such as permeability, osmotic pressure, and impermeant membrane are labeled.

Three-panel diagram showing the diffusion of chloride and potassium ions across a semipermeable membrane. Panel A illustrates movement driven by a concentration gradient, panel B shows both concentration gradient and opposing electrostatic force, and panel C depicts equilibrium potential where forces balance and ion flow is stable. Chloride ions are marked in blue, potassium ions in red, with direction arrows indicating ion movement.

ion permeance and action potential

Diagram showing the chemical transmission of nerve impulses at a synapse, with labeled steps illustrating neurotransmitter release from the presynaptic terminal, movement across the synaptic cleft, binding to postsynaptic channel receptors, and resulting signal propagation in the nervous system.

Follow the electrical and chemical changes undergone to transmit an impulse through the human nervous system

Hear a neuroscientist Christof Koch speaks about how a neuron identifies selective encoding and coding to specific memories

What happens to a person's biological clock in isolation?

How does the human body perceive and respond to pain?

See All Videos and Images →

Topics

human sensory reception human ear taste bud nervous system disease stimulus-response behaviour nervous system disease neuroscience neurotoxin neurology Organ muscle immune system Circulatory system Respiratory system Integument Endocrine system mucous membrane gland Physiology Anatomy

Dig Deeper: More Articles That Discuss This Topic

Key People

default image

David Hunter Hubel

American biologist

default image

Roger Wolcott Sperry

American biologist

Ivan Pavlov

Ivan Pavlov

Russian physiologist

Galen of Pergamum

Galen

Greek physician

default image

Johannes Müller

German physiologist

default image

Torsten Wiesel

Swedish biologist

Sir Charles Sherrington

Sir Charles Scott Sherrington

British physiologist

default image

D. Carleton Gajdusek

American physician

default image

Vladimir Bekhterev

Russian psychiatrist

Jean-Martin Charcot

Jean-Martin Charcot

French neurologist

John Hughlings Jackson, oil painting by Lance Calkin; in the London Hospital Medical College

John Hughlings Jackson

British physician

default image

Robert Remak

German embryologist and neurologist

Thomas Willis, engraving by G. Vertue, 1742, after a portrait by D. Loggan, c. 1666

Thomas Willis

British physician

default image

Auguste-Henri Forel

Swiss psychiatrist

Duchenne, Guillaume-Benjamin-Amand

Duchenne de Boulogne

French neurologist

default image

Erasistratus Of Ceos

Greek physician

default image

Magnus Gustaf Retzius

Swedish anatomist and anthropologist

Sir Charles Bell, detail of a portrait by John Stevens, oil on canvas, c. 1821; in the National Portrait Gallery, London.

Sir Charles Bell

British anatomist

3d illustration human heart. Adult Anatomy Aorta Black Blood Vessel Cardiovascular System Coronary Artery Coronary Sinus Front View Glowing Human Artery Human Heart Human Internal Organ Medical X-ray Myocardium

Human Organs