SOMATOSENSORY RECEPTORS AND THEIR CNS CONNECTIONS

Bruce Lynn
Department of Physiology. University College London. London. WC I. England

INTRODUCTION

This review deals with recent findings concerning the properties of receptor units in the somatosensory system and the connections of their afferents in the central nervous system. Frequent references are made to articles in the recently published Volume II of the Handbook of Sensory Physiology (72). I have divided this review into four main sections, corresponding roughly to the subdivisions of kinesthesis, touch and pressure, warm and cold, and pain.

LIMB MOVEMENT AND POSITION

Three main groups of receptors send information to the central nervous system about the position of the limb and about changes in its position. These are the stretch receptors in skeletal muscles· and tendons, the mechanoreceptors in the joints, and certain of the skin mechanoreceptors. Cutaneous mechanoreceptors, which appear to play only a small part in kinesthesis (34) and are not usually considered as proprioceptors, are dealt with in the next section. However, it is worth noting that many hair receptors must fire during limb movements and that slowly adapting Type II receptors are excited by joint movements and must be capable of transmitting information about both movements and the fixed position of a limb (30, 84).

-Afferent Inflow from Joints
-Central Connections o[ Joint Afferents
-Muscle Stretch Receptors
-Central Connections 0/ Muscle Stretch Receptors
NON-NOXIOUS MECHANICAL EVENTS ON THE SKIN

-Properties of Afferent Mechanoreceptor Fibers
-Central Connections of Mechanoreceptor A./ferents in Spinal Cord
-Connections of Mechanoreceptor Afferents in the Trigeminal Nucleus
-Mechanically Excited Units in the Dorsal Columns, Dorsal Column Nuclei; and Medial  Lemniscus
SKIN TEMPERATURE: WARM AND COLD
-Afferent Thermoreceptor Units Responding to Skin Cooling
-Afferent Thermoreceptor Units Responding to Skin Warming
-Central Connections of Thermoreceptor A./Jerents

NOXIOUS SKIN STIMULATION

-Receptor Units
-Central Connections of Nociceptor Afferents