There has been extensive research on the identification and characterization of the spinal cord interneurons based on factors such as location, size, structure, connectivity, and function.

For instance, in the spinal cord of a 19-day-old rat embryo, at least 17 different subclasses of interneurons with ipsilateral axon projections were found.

In 1952, the grey matter of the cat's spinal cord was investigated, and it was shown to have ten distinct zones referred to as Rexed laminae.

[6] In addition, in the ventral half of the neural tube, four classes of (CPG) interneurons known as V0, V1, V2, and V3 neurons are generated.

[7] Human studies since the 1970s have documented how this integration of motor commands and sensory feedback signals is used to control muscle activity during movement.

[7] During locomotion, the sum of convergent inputs from the central pattern generator (CPG), sensory feedback, descending commands and other intrinsic properties turned on by different neuromodulators give rise to the activity of the interneurons.

[8] The sensory information that is transmitted to the spinal cord is modulated by a complex network of excitatory and inhibitory interneurons.

[13] Moreover, the connections to the Ia inhibitory interneurons may modulate the strength of the reciprocal inhibition to the antagonist motor neuron.

[13] Joints are controlled by two opposing sets of muscles called extensors and flexors that must work in synchrony to allow proper and desired movement.

[14] When tension is applied to a muscle, group Ib fibers that innervate the Golgi tendon organ are activated.

[14] This spinal interneuron makes an inhibitory synapse onto the alpha motor neuron that innervates the same muscle that caused the Ib afferent to fire.

[14] The reflex circuit involves the activation of the Group III afferents of pain receptors due to a stimulus affecting a limb, e.g. a foot.

These afferents enter the spinal cord and travel up to the lumbar region, where they synapse an excitatory interneuron.

A branch of the Group III afferent synapse an excitatory interneuron, which extends its axon across the midline into the contralateral spinal cord.

At that location, the interneuron excites the alpha motor neurons that innervate the extensor muscles of the opposite leg.

[14] A group of commissural interneurons present in lamina VIII in mid-lumbar segments mediates excitation of contralateral motoneurons by reticulospinal neurons.

[9] These neurons receive monosynaptic inputs from ipsilateral reticular formation and are not directly activated by group II afferents.

[15] Another class of lamina VIII commissural neurons includes a group that is activated by both reticulospinal and vestibular systems.