Cerebral Synaptic Mechanisms

Classical neurohistology revealed that the cerebral cortex is composed of nerve cells resembling in their essential features nerve cells at lower levels of the nervous system, but differing from these lower levels in the immense complexity of neuronal organization. We have just heard from Dr. Colonnier that the much finer structural features of synapses observed with electron microscopy have also shown a remarkable similarity through the whole nervous system; and this is particularly the case with chemically transmitting synapses. The presynaptic component contains synaptic vesicles and mitochondria and the 200 Â synaptic cleft is bounded by membranes displaying patches of thickening that may be assumed to be the active zones for chemical synaptic transmission. It would therefore be expected that physiological mechanisms of synaptic action would be comparable at all levels of the nervous system. There is as yet no evidence of electrical synaptic transmission at the higher levels of the central nervous system.

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