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

neurons A neuron (American English), neurone (British English), or nerve cell, is an membrane potential#Cell excitability, excitable cell (biology), cell that fires electric signals called action potentials across a neural network (biology), neural net ...

that are not specifically 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, spinal cord and retina. The CNS is so named because the brain integrates the received information and coordinates and influences the activity o ...

(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 allows the brain to perform complex functions such as

learning Learning is the process of acquiring new understanding, knowledge, behaviors, skills, value (personal and cultural), values, Attitude (psychology), attitudes, and preferences. The ability to learn is possessed by humans, non-human animals, and ...

and

decision-making In psychology, decision-making (also spelled decision making and decisionmaking) is regarded as the Cognition, cognitive process resulting in the selection of a belief or a course of action among several possible alternative options. It could be ...

Structure

In the

human brain The human brain is the central organ (anatomy), organ of the nervous system, and with the spinal cord, comprises the central nervous system. It consists of the cerebrum, the brainstem and the cerebellum. The brain controls most of the activi ...

, approximately 20–30% of the neurons in the

neocortex The neocortex, also called the neopallium, isocortex, or the six-layered cortex, is a set of layers of the mammalian cerebral cortex involved in higher-order brain functions such as sensory perception, cognition, generation of motor commands, ...

are interneurons, and the remaining majority of neurons are pyramidal. 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 identifyin
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 cells) * Golgi cells * Granule cells * Lugaro cells * Unipolar brush cells

Striatum

* Parvalbumin-expressing interneurons * Cholinergic interneurons * Tyrosine hydroxylase-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 Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid. Glycine is one of the proteinogenic amino acids. It is encoded by all the codons starting with GG (G ...

. However, excitatory interneurons using

glutamate Glutamic acid (symbol Glu or E; known as glutamate in its anionic form) is an α-amino acid that is used by almost all living beings in the biosynthesis of proteins. It is a Essential amino acid, non-essential nutrient for humans, meaning that ...

in the CNS also exist, as do interneurons releasing neuromodulators like

acetylcholine Acetylcholine (ACh) is an organic compound 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 ...

. In addition to these general functions, interneurons in the insect CNS play a number of specific roles in different parts of the nervous system, and also are either excitatory or inhibitory. For example, in the olfactory system, interneurons are responsible for integrating information from odorant receptors and sending signals to the mushroom bodies, which are involved in learning and memory. In the visual system, interneurons are responsible for processing motion information and sending signals to the optic lobes, which are involved in visual navigation. Interneurons are also important for coordinating complex behaviors, such as flight and locomotion. For example, interneurons in the thoracic ganglia are responsible for coordinating the activity of the leg muscles during walking and flying. Interneurons' main function is to provide a neural circuit, conducting flow of signals or information between sensory neurons and motor neurons.

References

{{Authority control Neurons