Last updated: Wed, Jun 21, 2017
Interneurons are by far the most common type of neuron whose cell body is found in the dorsal horns. Lamina I, which contains the largest number of ascending projection cells, is nevertheless 95% interneurons. Nearly all the cells in lamina II are interneurons. Several classes of interneurons have been identified by shape. Some extend mostly across the laminae, while others extend mostly up and down the cord. Some spread out mostly within a single lamina. Nearly all of the interneurons have many branches with many synapses, indicating that their function is to communicate among many neurons.
Propriospinal cells are interneurons whose axons extend between segments, in many cases across several segments. About half of the ascending/descending fibers in the cord are these propriospinal cells, rather than ascending or descending projection cells.
Both excitatory and inhibitory interneurons have been found. Interneurons have been found that excite ascending projection cells, and others have been found that inhibit them. Interneurons have been found that excite and inhibit other interneurons.
Most interneurons are wide dynamic range neurons. They respond to stimuli ranging from light touch to very intense pressure.