Neurons are specialized cells that receive and transmit information in the nervous system. They communicate using electrical changes across their cell membranes and chemical signals at many of the junctions between cells. Networks of neurons help make sensation, movement, memory, thought, and many automatic body functions possible.
The basic parts of a neuron
A typical neuron has a cell body, branching dendrites, and an axon. The cell body contains the nucleus and much of the machinery that keeps the cell alive. Dendrites commonly receive signals from other cells. The axon carries electrical signals away from the cell body toward other neurons, muscles, or glands.
Some axons are wrapped in myelin, an insulating material made by glial cells. Myelin helps electrical impulses travel efficiently along the axon. Gaps in the myelin allow the signal to be regenerated as it moves.
How an electrical signal travels
Neurons maintain differences in electrically charged ions across their membranes. When incoming signals change the membrane voltage enough to reach a threshold, many neurons generate an action potential. This is a rapid, self-propagating change in voltage that travels along the axon.
The strength of an action potential is not a simple analog measure of thought or sensation. Information in nervous systems is encoded through patterns such as which neurons fire, how often they fire, when they fire relative to one another, and how networks are connected.
What happens at a synapse?
At many synapses, an arriving electrical signal triggers the release of chemical messengers called neurotransmitters. The molecules cross a very small gap and bind to receptors on another cell. Depending on the transmitter, receptor, and circuit, the receiving cell can become more or less likely to generate its own electrical signal.
Not every synapse is chemical. Electrical synapses can connect cells more directly through channels that allow current to pass between them.
Different kinds of neurons
Broad functional categories include sensory neurons, motor neurons, and interneurons. Sensory neurons carry information about stimuli toward the central nervous system. Motor neurons communicate with muscles. Interneurons form enormous networks within the brain and spinal cord and help integrate information.
These categories hide tremendous diversity. Neurons vary in shape, molecular identity, connections, firing patterns, and function. Modern neuroscience increasingly classifies cell types using combinations of anatomy, gene expression, physiology, and connectivity.
Neurons do not work alone
Glial cells support and regulate the environment around neurons. Different glia help form myelin, maintain chemical conditions, participate in immune responses, and influence synaptic function. Brain function emerges from interactions among neurons, glia, blood vessels, and many other biological systems.
