Composition of the medial and posterior articular nerves of the mouse kneejoint

The number and the distribution of fiber size in the medial (MAN) and poste rior (PAN) articular nerves of the mouse knee joint were studied by electro n microscopy. The MAN contained 75 +/- 28 nerve fibers consisting of 63 +/- 24 unmyelinated and 12 +/- 6 myelinated fibers. The PAN was composed of 19 5 +/- 50 nerve fibers, namely 129 +/- 28 unmyelinated and 66 +/- 24 myelina ted fibers. A skewed unimodal distribution of the unmyelinated nerve fiber diameters was seen in both nerves ranging from 0.1 to 1.2 mum with a maximu m between 0.3 and 0.6 mum. The myelinated nerve fibers in the MAN ranged fr om 1 to 8 mum with a peak between 2 and 5 mum. In the PAN, their diameters ranged from 1 to 12 mum with a clearly visible peak at 4-5 mum and a platea u at 8-9 mum 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 r at concerning the types of nerve fibers and the composition of the two nerv es. However, in relation to the much smaller area of tissue to be innervate d the total number of primary afferents is considerable smaller in the mous e.