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The mechanism of the reflex arc. (Relay neuron labeled at right center. Diagram discusses the PNS definition.)
MeSH Interneurons

An interneuron (also called relay neuron, association neuron or local circuit neuron) is a multipolar neuron which connects afferent neurons and efferent neurons in neural pathways. Like motor neurons, interneuron cell bodies are always located in the central nervous system (CNS).



When contrasted with the peripheral nervous system (PNS), the neurons of the central nervous system (CNS), including the brain, are all interneurons. However, in the CNS, the term interneuron is used for small, locally projecting neurons (in contrast to larger projection neurons with long-distance connections). CNS interneurons are typically inhibitory, and use the neurotransmitter GABA or glycine. However, excitatory interneurons using glutamate also exist, as do interneurons releasing neuromodulators like acetylcholine.

Examples of interneurons include the sensory neuron and motor neuron also connecting to the brain through the association neurons. This is theorized to help focus higher attention on relevant sensory input and help block out behaviorally irrelevant or unchanging input, such as the sensation of the backs of your thighs on a chair. The neurophysiological measure short-latency intracortical inhibition (SICI) is believed to be mediated by these inhibitory interneurons.[citation needed]

In 2008, a nomenclature for the features of GABAergic cortical interneurons was proposed, called Petilla terminology.[1]


Spinal interneurons

  • 1a Inhibitory Neuron: Found in Lamina VII. Responsible for inhibiting antagonist motor neuron. 1a spindle afferents activate 1a inhibitory neuron.
  • 1b Inhibitory Neuron: Found in Lamina V, VI, VII. 1b afferent or Golgi tendon organ activates it.

Cortical interneurons

  • Parvalbumin-containing interneurons
  • CCK-containing interneurons
  • VIP-containing interneurons

Cerebellar interneurons


  1. ^ Ascoli GA, Alonso-Nanclares L, Anderson SA, et al (July 2008). "Petilla terminology: nomenclature of features of GABAergic interneurons of the cerebral cortex". Nat. Rev. Neurosci. 9 (7): 557–68. doi:10.1038/nrn2402. PMID 18568015. 

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