Fused neurons and synaptic contacts in the giant nerve fibres of cephalopods

Abstract

The fact that there are two very large nerve cells in the central nervous system of the squid, Loligo , was discovered by Williams (1909), who also gave a brief description of their connexions. His account appears never to have been amplified, or indeed even mentioned, by any subsequent worker until these enormous nerve fibres were accidentally rediscovered in 1933 (see Young 1935 a , 1936 a, b, c ). Williams considered that the whole giant-fibre system on each side of the body consists of the processes of one of the two main giant cells. In fact the arrangement is much more complicated than this, and contains two curiously opposite features of the greatest interest for the neurologist (Young 1936 £). First, the processes of the two main giant cells provide a clear case of the complete fusion of the axons of two nerve cells, thus infringing the strict canon of the neuron theory. Nevertheless, and this is the second point, there are also present, elsewhere in the system, discontinuous synapses which are perhaps more clear and easy to study than any yet described.