Interneurons and proprioneurons in the adult human spinal grey matter and in the general somatic and visceral afferent cranial nerve nuclei.

Using the classification of Abdel-Maguid & Bowsher (1984), interneurons of the dorsal horn of the grey matter of the human spinal cord and medulla oblongata were found to belong to only three 'families' of neurons, out of a possible thirteen. This is in itself one of the justifications for the method of classification. Functional identification of these human neurons has been made on the basis of topological, morphological and projectional comparison with known cells in other mammalian species. Among the cells identified are gelatinosal interneurons and Renshaw cells of laminae VII and VIII. Neurons belonging to the same 'family' as Waldeyer cells of lamina I continue around the outer edge of the grey matter, their dendrites forming a part of the boundary between grey and white matter. Interneurons with small and very small dendrite fields lie on interlaminar boundaries and have mediolaterally oriented dendrites, in contrast to the craniocaudally oriented dendritic field of most dorsal horn neurons. If such dendrites lying along interlaminar boundaries are also found to exist in other species, it may explain the abrupt change in physiological characteristics which is found on passing an electrode from one lamina to another.