Afferent fibres from muscle receptors in the posterior nerve of the cat's knee joint.

The properties of some receptors with afferent fibres in the cat's posterior knee joint nerve have been examined, especially those discharging tonically with the joint in intermediate positions between full flexion and extension. Some of these receptors behave like muscle spindles, and respond to manoeuvres which stretch popliteus muscle. Both in single unit and whole nerve recordings their discharge pauses during a popliteus twitch, and can be strikingly augmented by tetanic stimulation of a number of popliteus fusimotor fibres isolated from ventral root filaments. The action of succinylcholine on these receptors closely resembles its effect on popliteus spindle units with fibres sited normally in the popliteus nerve. Other units with properties suggesting origin from popliteus tendon organs were also observed; their fibres and those of the spindle units conducted at Group I velocity. It is concluded that some afferent fibres from popliteus spindles and possibly tendon organs commonly pursue an aberrant course in the posterior articular nerve of the knee joint.