The motorneuron surface

Abstract

It is possible to reveal all the terminal boutons on the ventral horn cells of the spinal cord after fixation with formalin, mordanting (Weigert-Pal), embedding in carbowax and staining with haematoxylin or by a silver method. The boutons are more numerous than has been supposed and cover the greater part of the surface of the nerve cell body and dendrites. Electron micrographs after osmium fixation show a thin membrane at the surface of the nerve cell body and dendrites. The boutons are closely apposed to this surface and are themselves covered by thin membranes. At the region of contact there is usually no separation visible, with the relatively low magnification used, between pre- and post-synaptic membranes. The boutons contain many bodies that absorb electrons strongly and are presumably mitochondria. The pre-synaptic nerve fibres are provided with relatively thick sheaths, except where they swell out to form boutons. The protoplasm of glia cells fills up all the space between the neuronal elements. No large tissue spaces or intercellular matrix appear. Exchanges between the neurons and capillaries presumably take place through the glial protoplasm.