The Axon Collaterals of Purkinje Cells

Abstract

The recurrent collaterals of Purkinje axons take their origin from the proximal as well as more remote parts of the axon. Thus, they can reach closely neighboring regions of the cortex within the same folium as well as in adjacent and even in rather remote folia. According to the classical description of Cajal (1911) the recurrent collaterals are myelinated and ascend in oblique direction through the deeper strata of the granular layer. Upon reaching the upper stratum of this layer they bend into a tangential direction, and by branching profusely they give rise to a dense plexus situated beneath the layer of the Purkinje cell bodies. This plexus is referred to generally as the “infraganglionic plexus”. Branches arising either directly from the Purkinje cell axons or from the infraganglionic plexus, ascend to the level above the Purkinje cell bodies, where another tangential plexus of myelinated fibers is established: the so-called “supraganglionic” plexus. The course of the fibers in the infraganglionic plexus is predominantly parallel to the transversal plane of the folium, but the supraganglionic plexus in the molecular layer is longitudinally orientated (Fig. 101). Under the EM the fibers, especially of the upper plexus, can be recognized easily from their myelin sheaths (Fox, Siegesmund and Dutta, 1964), there being no other myelinated fibers in the molecular layer except the rare Cajal-Smirnov fibers.