No abstract

SUMMARY1. The conduction velocities of 278 posterior articular nerve fibres studied in dorsal root filaments ranged from 10 to 110 m/sec. The conduction velocities were distributed similarly to posterior articular nerve fibre diameters determined histologically.2. Two hundred and nine fibres were slowly adapting. Of these, 140 responded only at both marked flexion and marked extension, forty-seven responded only during flexion and twelve only during extension. Four slowly adapting fibres were activated specifically at intermediate joint positions. Outward twist of the tibia (abducting the foot) enhanced the discharge of most slowly adapting joint fibres.3. Two rapidly adapting receptor types were noted. Pacinian corpusclelike receptors (fourteen fibres) responded transiently to joint movement in any direction regardless of initial position. Phasic joint receptors (thirty fibres) were rapidly adapting at most joint positions but could give a low rate sustained discharge when strongly stimulated.4. Six slowly adapting posterior articular nerve fibres responded to succinylcholine, suggesting that they originated from muscle spindles. Spindle-like receptors were usually tonically active at intermediate joint positions.5. Eleven slowly conducting myelinated fibres responded only to extreme joint movement, which was probably noxious.

We studied proprioception with the ankle joint and the metacarpophalangeal (MCP) joint of the index finger of humans by use of a method that could distinguish a position sense from a movement sense. The test measured how subjects' ability to detect a fixed displacement of a joint varied with the rate of joint rotation. A position sense should not depend on the speed of joint placement; therefore slow rates of movement should not degrade subjects' ability to sense joint displacements. However, in the absence of a position sense, subjects would presumably rely on movement signals that do depend on the rate of rotation, and their ability to detect displacements should decrease when rate decreases. Subjects could sense small displacements of the ankle (+/- 3.5 degrees) and the MCP joint (+/- 2.5 degrees lateral excursions) with no decrement in performance at speeds as low as 0.25 degrees/min for the ankle and 0.5 degrees/min for the MCP joint (the slowest tested thus far). The findings confirm the existence of a position sense with these joints. Block of the ulnar nerve at the wrist, which paralyzes the interosseous muscles that adduct and abduct the MCP joint but presumably leaves skin and joint mechanisms unaffected, substantially impaired subjects' ability to detect the lateral excursions at slow speeds. Performance fell sharply at speeds less than 128 degrees/min and leveled off at approximately 20% detections at speeds less than 4 degrees/min. Increasing displacement to +/- 7 degrees did not improve performance. Block of the common peroneal nerve at the knee, which paralyzes the ankle dorsiflexor muscles, substantially impaired subjects' ability to detect the +/- 3.5 degrees displacements at slow speeds when the foot was positioned to slacken the plantarflexion muscles (which were not affected by the block). Performance fell sharply at speeds less than 256 degrees/min and approached zero at speeds less than 16 degrees/min. However, positioning the foot to stretch the plantarflexor muscles restored subjects' performance to near normal. Local anesthetic injected into the MCP joint space produced no observable effect on the ability to detect either slow or fast excursions. The joint anesthesia went unnoticed by the subject. We conclude that independent and separable senses exist for limb position and limb movement and that normal position sense requires sensory inputs from the muscles.

No abstract

Afferent activity in the lateral (LAN), medial (MAN), and posterior (PAN) articular nerves supplying the cat knee joint was studied at intermediate positions of the joint that included most of its working range. The discharge was analyzed only while the joint was stationary. The small LAN showed negligible tonic activity at intermediate angles (as determined by gross recording) and was not studied further.