Morphological characteristics of the innervation of the cat's knee joint.

The peripheral and central terminals of primary afferents of the cat's knee joint were studied with light- and electron microscopy (including HRP-transport methods). The majority of these afferent fibres are unmyelinated or thinly myelinated. In the periphery, they terminate in non-corpuscular endings. A dense network of branching nerve fibres surround the blood vessels to terminate at the vessel walls or in the adjacent dense collagenous tissue. Besides the terminals the fibres show preterminal bulges which are assumed to represent additional transduction sites. This implies that the whole distal fibre portion has a receptive function. The spinal projection is located in lamina I and V-VII of the dorsal horn. This location parallels that of muscular and visceral fibres, pointing to the possibility of a common projection pattern for deep somatic afferent fibres in the spinal cord of the cat.