Neuronal and glial processes in neuropathology

The cells of the nervous system can be characterized by their well formed cell processes and by the cell-to-cell relationships that they form. The neuron displays essentially cylindrical processes, i.e. round in cross section, which form synaptic junctions with either other neuronal processes or with other target cells. A variety of pathologic processes involve alterations of either the neuronal processes or the synapses.

On the other hand, the functional, peripheral portions of the processes of the glial cells are largely sheet-like in nature. Frequently, the connecting link between the functional sheet-like process and the glial cell body is round in section like the neuronal process, but the peripheral parts of the process are not. Thus, the interfascicular oligodendroglial cell elaborates several sheet-like processes, each of which forms a segment of the myelin sheath. An unusual cell junction, the transverse bands is present at the interface of the oligodendroglial process and the axonal surface. Numerous pathological alterations occur in the oligodendroglial cells that may lead to demyelination. These may sometimes be the result of defects in the glial process, conceivably in the transverse bands or the tight junction which isolates the interlamellar spaces from the extracellular space.

Finally, the astrocytes, too, form elaborate sheet-like processes that separate most of the central nervous system from the mesodermal and mesenchymal tissues as well as surround some neuronal surfaces, including certain synapses. Gap junctions and other adhesive devices are found between astrocytic processes. Several pathological conditions are characterized by defects or anomalies in the astrocytic periphery.