Ultrastructural features of human cerebral cortex.

Neuronal and glial elements have been examined in the temporal or frontal cortex of four brains with normal parenchyma. The identifying features recognized in animal brains have been found valid in human cortex for stellate and pyramidal neurons and their dendrites, spines, synapses, initial segments of axons, nodes of Ranvier and axon terminals; also for astrocytes, oligodendrocytes of various electron densities, pericytes, blood vessels and basement lamina, and for the relation of subarachnoid space to arterioles. However, most microglial cells have unexpectedly sparse and pale cytoplasm with few organelles, and the distribution of glial nuclear chromatin is not entirely in accordance with that described in animal brains. Fusiform neurons have been identified, and their cytoplasm resembles that of stellate cells. Peculiarities of human cortex include a nuclear inclusion that is present in stellate neurons only. Two neuronal cell-body profiles were myelinated, and a blood capillary was seen to penetrate a neuron. Somatic spines were found occasionally with or without synapses. Ribosomes can be present in axons, espicially at nodes of Ranvier, and a small portion of axon terminals contain a variety of dense bodies of which some are derived from mitochondria. Endoplasmic reticulum can occur in a compressed stack in neurons, and an unusual vesicular organelle has been seen in dendrites, axons and somata. Astrocytes as well as oligodendrocytes and occasional microglial cells act as satellites to neurons, and the exchange of a membrane-bound body between a neuron and asatellite glial cell is illustrated. Some dark pycnotic neurons were present, and it was remarkable that a closely apposed neuron could be entirely normal. These findings are compared with published descriptions of cortical ultrastructure in the brains of laboratory animals.