Neuron

Definition

An electrically excitable cell that generates and transmits action potentials through specialized projections, forming the functional unit of nervous systems. In arthropods, neurons range from giant fibers mediating escape reflexes—such as the cockroach's cercal giant interneurons that trigger evasive turning in milliseconds—to minute local interneurons integrating chemosensory input in the antennal lobe. Arthropod neurons typically exhibit unipolar or bipolar morphologies with cell bodies often displaced to the periphery of ganglia, contrasting with the multipolar architecture common in vertebrates.

Etymology

From Greek neuron, sinew, tendon, nerve

Example

The descending contralateral movement detector (DCMD) neuron in locusts integrates visual looming stimuli and commands the hindleg extension that powers the jump escape response.

Synonyms

• neurone
• nerve cell

Related Terms

• ganglion
• Synapse
• Axon
• Dendrite
• interneuron
• Sensory neuron
• motor neuron
• neuroglia
• Action potential
• compound eye
• mechanoreceptor

Usage Notes

In arthropod literature, 'neuron' predominates over 'neurone.' The term excludes neuroglial cells (glia), which provide metabolic and structural support but do not generate action potentials. Sensory neurons (afferent), interneurons (associative), and motor neurons (efferent) describe functional classes; morphology is described separately (unipolar, bipolar, multipolar). Giant neurons in invertebrates permit rapid, reliable signaling over long distances but sacrifice information-coding capacity compared to populations of small neurons.