Primary sensory neurons in the central nervous system.

Published data and our own results relating to exteroceptor and a variety of interceptor neurons in the brain and spinal cord, such as intraspinal Hesse ocelli and light-sensitive epiphyseal and ependymal neurons, are presented. Light-sensitive ganglion neurons in invertebrates are also described, along with intrinsic spinal cord bipolar sensory neurons within the spinal cord, primary chemo-and thermosensitive neurons, and sensory unipolar neurons associated with the three fine "central nerves" of Motavkin, which perforate the sheath of the spinal cord and ending with bush-like receptors close to vessels or near the ependyma of the central canal. Data on all known intracortical interoceptors in vertebrates are generalized into a single scheme. It is hypothesized that the brains of animals and humans have an intrinsic sensory innervation comparable with the innervation of other organs and containing local primary sensory neurons and their asynaptic dendrites, which can be divided into two groups: interceptor and exteroceptor.