neuron
Meaning of neuron: The cell behind every thought and every movement, and the one the adult brain almost never replaces once it is lost.
Definition of neuron
A neuron is the signaling cell of the nervous system, built to receive information at one end, weigh it, and pass it on at the other. Branching arms called dendrites collect incoming signals, the cell body adds them up, and a single long fiber called the axon carries the result away. Most neurons communicate with other neurons rather than with the body directly.
How does a signal actually travel?
Not as a current running along a wire. The membrane of the axon holds charged particles unevenly on its two sides, and a signal is a wave in which gates open, particles rush across, and the imbalance flips and then resets. Each patch of membrane sets off the next, so the wave rebuilds itself as it goes and arrives at the far end as strong as it began. Where the fiber is wrapped in a fatty sheath, the wave jumps between gaps in the wrapping and travels far faster, which is why damage to that sheath slows or blocks conduction.
How do two neurons pass a message on?
They do not touch. At a synapse a narrow gap separates them, and the electrical wave arriving at the end of one cell triggers the release of a chemical messenger into that gap. The messenger drifts across, attaches to receptors on the far side, and either encourages or discourages the next cell from firing. A single cell receives thousands of such inputs and fires only when the encouraging ones outweigh the rest. Nearly every drug that acts on the brain works somewhere in this chemical step rather than on the electrical one.
What kinds are there?
| Type | Direction of traffic |
|---|---|
| Sensory | From skin, eye, ear and organs toward the cord and brain |
| Motor | From the brain and cord out to muscle and gland |
| Interneuron | Between cells within the brain and cord, and by far the most numerous |
The term nerve cell means the same thing. A nerve is something different again: a bundle of axons wrapped together, not a cell. Mature neurons rarely divide, which is why tissue lost to a stroke is not replaced and why a primary brain tumor in an adult almost always arises from the supporting glial cells rather than from the neurons themselves.
Also known as
Used in a sentence
The disease progressively destroys motor neurons in the spinal cord.
Good to know
Signals move within a neuron as a self-renewing wave of ion movement across the membrane and between neurons as a chemical released across a gap, so most drugs acting on the nervous system work at the chemical step.
Word origin
Where “neuron” comes from
Neuron is the Greek word for a sinew or cord, later applied to the fibers of a nerve and then to the individual cell.