Interneurons (also called internuncial neuron, relay neuron, association neuron, connector neuron, intermediate neuron or local circuit neuron) are a broad class of neurons found in the human body. Interneuron creates neural circuits, enabling communication between sensory or motor neurons and the central nervous system (CNS). They have been found to function in reflexes, neuronal oscillations, and neurogenesis in the adult mammalian brain. Interneuron can be further broken down into two groups: local interneuron and relay interneuron.

Local interneuron has 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. The interaction between interneurons allows the brain to perform complex functions such as learning, and decision-making.

Interneurons/Interneurons Definition

Interneuron (also known as association neurons) are neurons that are found exclusively in the central nervous system. That means that they are found in the brain and spinal cord and not in the peripheral segments of the nervous system. There are more than 100 billion interneurons in the human body, which makes them the most abundant of the three major neuron types (along with sensory and motor neurons). This abundance of interneuron is due to the complexity of integrating the sensory and motor segments of the nervous system and the diversity of functions that exist in the brain and spinal cord.


Interneurons Function

As with all neurons, interneuron is able to stimulate tissues through the use of neurotransmitters, or chemical messengers; however, for the purpose of integration, interneuron utilizes different neurotransmitters than the peripheral nervous system uses. Typically, interneuron will release glutamate, an excitatory neurotransmitter, to activate tissues in a reflex response. Similarly, they may utilize gamma-aminobutyric acid (GABA) when inhibition of tissue is necessary.

Interneurons Structure

Unlike the peripheral nervous system (PNS), the central nervous system, including the brain, contains many interneuron. 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 are impeded by the inability to isolate cell populations born at different times for gene expression analysis. An effective means of identifying a coetaneous interneuron is neuronal birthdate. This can be achieved using nucleoside analogs such as EdU.

In 2008, a nomenclature for the features of GABAergic cortical interneuron was proposed, called Petilla terminology.

Spinal cord Interneurons
Spinal cord Interneurons

Spinal cord

Ia inhibitory interneuron: Found in [[rexed laminae#Laminae|lamina VII. Responsible for inhibiting antagonist motor neurons. 1a spindle afferents activate 1a inhibitory neurons.
Ib inhibitory interneuron: Found in lamina V, VI, VII. Afferent or Golgi tendon organ activates it.


Parvalbumin-expressing interneuron
CCK-expressing interneurons
VIP-expressing interneurons
SOM-expressing interneurons

Cortex Interneurons
Cortex Interneurons


Molecular layer (basket cells, stellate cells)
Golgi cells
Granule cells
Lugaro cells
Unipolar brush cells


Parvalbumin-expressing interneuron
Cholinergic interneurons
Tyrosine hydroxylase-expressing interneuron
Calretinin-expressing interneurons
Nitric oxide synthase-expressing interneuron


What Are Interneurons?

An Interneuron (Also Called Internuncial Neuron, Relay Neuron, Association Neuron, Connector Neuron, Intermediate Neuron Or Local Circuit Neuron) Is A Broad Class Of Neurons Found In The Human Body.

What Do Interneurons Do?

Interneuron Create Neural Circuits, Enabling Communication Between Sensory Or Motor Neurons And The Central Nervous System (Cns). They Have Been Found To Function In Reflexes, Neuronal Oscillations, And Neurogenesis In The Adult Mammalian Brain.

What Is The Role Of Central Pattern Generators In Movement?

Central Pattern Generators And The Control Of Rhythmic Movements. Central Pattern Generators Are Neuronal Circuits That When Activated Can Produce Rhythmic Motor Patterns Such As Walking, Breathing, Flying, And Swimming In The Absence Of Sensory Or Descending Inputs That Carry Specific Timing Information.

Where Are Interneuron Found?

Nerve Cells Are Not Limited To The Brain. They Exist Throughout The Central Nervous System (Cns: Including Brain And Spinal Cord) As Well As The Peripheral Nervous System (Sensory And Motor Neurons) Which ‘starts’ But Extends ‘outward’ From The Spinal Cord To Our Internal Organs, Limbs, Etc.

Where Is The Structural Link Between The Cns And Pns Located?

Where Is The Structural Link Between The Cns And Pns Located? In The Gray Matter Of The Cns In Motor Neurons In The Ventral Root Of The Spinal Nerve In Sensory Neurons In The Dorsal Root And Dorsal Root Ganglia Only In The Cerebral Cortex.