Ultrastructure of transitional region of the human eighth cranial nerve.

The transitional region of the eighth cranial nerve, where the central and peripheral nervous tissues are contiguous, was studied by electron microscopy using surgically resected specimens of the human eighth cranial nerve root. The astrocytic glial dome was sharply demarcated by a basement membrane from the peripheral portion of the nerve. Half-desmosomes were found on the edge of the astrocytic glial dome and at the luminal surface of the perivascular glial limiting membrane. Desmosomes and gap junctions were found between the astrocytic processes. These ultrastructural features suggest a weak link between the central and peripheral portions of the nerve which might predispose the transitional region to injury, although the peripheral and central portions have sufficient resistance to external stresses independently.