On the structure of IIIab-pyramidal cells in the human isocortex. A Golgi and electron microscopical study with...

In Golgi preparations of the adult human frontal cortex the IIIab-pyramidal cells show an apical dendrite with numerous side branches and several bifurcating basal dendrites. The dendrites are covered with numerous stalked spines. The axon takes a descending course giving rise to several collaterals. Ultrastructurally the proximal axon segment, i.e. the axon hillock and the initial segment, corresponds in a large degree to descriptions given for that of animals, including the tripartite substructure of the dense undercoating of the axolemma. In the human IIIab-pyramidal cells along the proximal part of the initial segment the undercoating displays gaps not only at the known sites but also opposite astroglial processes. The IIIab-pyramidal cells of the human isocortex require particular interest because they show almost exclusively a recently reported, age-related alteration of their proximal axon segment.