Interneurons (also called internuncial neurons, relay neurons, association neurons, connector neurons, intermediate neurons or local circuit neurons) are

neurons A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa ...

that connect two brain regions, i.e. not direct motor neurons or sensory neurons. Interneurons are the central nodes of neural circuits, enabling communication between sensory or motor neurons and the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all p ...

(CNS). They play vital roles in reflexes, neuronal oscillations, and neurogenesis in the adult mammalian brain. Interneurons can be further broken down into two groups: local interneurons and relay interneurons. Local interneurons have short axons and form circuits with nearby neurons to analyze small pieces of information. Relay interneurons have long axons and connect circuits of neurons in one region of the brain with those in other regions. However, interneurons are generally considered to operate mainly within local brain areas. The interaction between interneurons allow the brain to perform complex functions such as

learning Learning is the process of acquiring new understanding, knowledge, behaviors, skills, values, attitudes, and preferences. The ability to learn is possessed by humans, animals, and some machines; there is also evidence for some kind of lea ...

, and decision-making.

Structure

In the neocortex (making up about 80% of the human brain), approximately 20–30% of neurons are interneurons. Investigations into the molecular diversity of neurons is impeded by the inability to isolate cell populations born at different times for gene expression analysis. An effective means of identifying coetaneous interneurons is neuronal birthdating. This can be achieved using nucleoside analogs such as EdU. In 2008, a nomenclature for the features of GABAergic cortical interneurons was proposed, called ''Petilla terminology''.

Spinal cord

* Ia inhibitory interneuron: Found in lamina VII. Responsible for inhibiting antagonist motor neuron. 1a spindle afferents activate 1a inhibitory neuron. * Anatomy and physiology of animals A reflex arc

Anatomy and physiology of animals A reflex arc

Ib inhibitory interneuron: Found in lamina V, VI, VII. Afferent or Golgi tendon organ activates it.

Cortex

* Parvalbumin-expressing interneurons * CCK-expressing interneurons * VIP-expressing interneurons * SOM-expressing interneurons

Cerebellum

* Molecular layer ( basket cells,

stellate cell Stellate cells are neurons in the central nervous system, named for their star-like shape formed by dendritic processes radiating from the cell body. Many stellate cells are GABAergic and are located in the molecular layer of the cerebellum. Ste ...

s) * Golgi cells * Granule cells * Lugaro cells * Unipolar brush cells

Striatum

* Parvalbumin-expressing interneurons * Cholinergic interneurons *

Tyrosine hydroxylase Tyrosine hydroxylase or tyrosine 3-monooxygenase is the enzyme responsible for catalyzing the conversion of the amino acid L-tyrosine to L-3,4-dihydroxyphenylalanine (L-DOPA). It does so using molecular oxygen (O2), as well as iron (Fe2+) and t ...

-expressing interneurons *Calretinin-expressing interneurons *Nitric oxide synthase-expressing interneurons

Function

Interneurons in the CNS are primarily inhibitory, and use the neurotransmitter GABA or glycine. However, excitatory interneurons using glutamate in the CNS also exist, as do interneurons releasing neuromodulators like

acetylcholine Acetylcholine (ACh) is an organic chemical that functions in the brain and body of many types of animals (including humans) as a neurotransmitter. Its name is derived from its chemical structure: it is an ester of acetic acid and choline. Par ...

. Interneurons main function is to provide a neural circuit, conducting flow of signals or information between a sensory neuron and or motor neuron.

References

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