Interneurons

Definition

Neurons that relay signals between sensory neurons and motor neurons, forming the integrative core of central nervous system circuits. In arthropods, interneurons process afferent input from mechanoreceptors, chemoreceptors, and photoreceptors before coordinating motor output, enabling complex behaviors such as escape responses, courtship displays, and navigational orientation.

Etymology

Example

In the escape response of the cockroach Periplaneta americana, wind-sensitive cercal hairs activate giant interneurons that synapse directly onto leg motor neurons, producing a directed turn-away in less than 50 milliseconds.

Synonyms

• relay neurons
• association neurons

Related Terms

• motor neurons
• sensory neurons
• Central nervous system
• neuropil
• ganglion
• reflex arc
• Protocerebrum

Usage Notes

In vertebrate neurobiology, 'interneuron' sometimes denotes inhibitory local-circuit neurons exclusively; in arthropod and invertebrate contexts, the term retains its broader classical meaning of any neuron interposed between sensory and motor pathways, whether excitatory or inhibitory. The distinction matters when comparing circuit diagrams across phyla.