Composition of the medial and posterior articular nerves of the mouse knee joint

Abstract

The number and the distribution of fiber size in the medial (MAN) and posterior (PAN) articular nerves of the mouse knee joint were studied by electron microscopy. The MAN contained 75 - 28 nerve fibers consisting of 63 - 24 unmyelinated and 12 - 6 myelinated fibers. The PAN was composed of 195 - 50 nerve fibers, namely 129 - 28 unmyelinated and 66 - 24 myelinated fibers. A skewed unimodal distribution of the unmyelinated nerve fiber diameters was seen in both nerves ranging from 0.1 to 1.2 w m with a maximum between 0.3 and 0.6 w m. The myelinated nerve fibers in the MAN ranged from 1 to 8 w m with a peak between 2 and 5 w m. In the PAN, their diameters ranged from 1 to 12 w m with a clearly visible peak at 4-5 w m and a plateau at 8-9 w m that may represent a second maximum. These data show that the knee joint innervation of the mouse is comparable to those of the cat and rat concerning the types of nerve fibers and the composition of the two nerves. However, in relation to the much smaller area of tissue to be innervated the total number of primary afferents is considerable smaller in the mouse.