Croonian Lecture - The elementary nervous system

Abstract

Nervous organization is found in a most elementary form in the sea-anemones. Their behaviour is brought about partly by specific muscles, partly by the mechanically complex operation of fields of muscle fibres. Stimulation causes conduction of all-or-nothing impulses to the muscles. Histological studies confirm and extend the early work of Sharpey-Schäfer on the organization of the coelenterate nerve-net. Much of the later histological work is vitiated by confusion of other fibrous structures with nerve cells. Both physiological and critical histological studies show" that the net is synaptic. Simple reflexes play only a limited part in actinian behaviour. There is evidence that several distinct kinds of spontaneous activity are built into the normal behaviour mechanisms. A response often consists of a prolonged change in pattern of spontaneous activity, rather than a reflex. The complexity and variety of physiological properties utilized in the behaviour of these animals is surprising and often recalls central nervous phenomena. Nevertheless, we are perhaps nearer a complete analysis of the structural units on which behaviour is based in these than in any other animals.