Organization and sensory properties of small myelinated fibres in the dorsal cervical rami of the cat.

A study using both anatomical dissection and electrophysiological recording has been made to analyse sensory components of the cervical dorsal rami in the cat. Particular attention has been paid to the physiological properties of Group III muscle afferents. The dorsal rami from C2 to C4 are composed of many nerve bundles that contain afferents from both muscle and skin. Bundles containing only cutaneous and only muscle afferents were identified and found to follow a relatively consistent pattern of organization within the ramus. In nerve bundles serving the biventer cervicis muscle, a population of Group III afferent fibres was identified that responded to strong localized pressure or localized stretch. Their receptive fields were generally small and situated on the muscle borders or in tendinous inscriptions. Such units comprised 73% of those with conduction velocities less than 20 m/s. Group III afferent fibres from neck muscles fired readily to intramuscular 6% sodium chloride, but were mostly not sensitive to bradykinin injected locally or intra-arterially.