User:Jtwsaddress42/Projects/Project 3/Sections/Chapter 2/Neuroid Tissues - Precursors To Nervous Activity

In 1970, the British-Canadien zoologist George Owen Mackie (October 20, 1929 - ) published Neuroid Conduction and the Evolution of Conducting Tissues in The Quarterly Review of Biology, where he explored the functional cellular precursors to nerves in protozoa, porifera, cnidaria, and other invertebrates. His studies in the behavioral physiology of these simple organisms revealed the relationship between electrical conduction in the cell and the initiation of a behavioral response.

Mackie defined Neuroid conduction as "the propagation of electrical events in the membranes of non-nervous, nonmuscular cells." He identifies examples of neuroid conduction in algae, simple and higher plants, and in the non-neural tissue of sponges, jellyfish, and ctenophores. This demonstration of non-neural conduction shows that depolarization is not a nervous system specialization, but rather the intrinsic potential of cells more broadly - it is, their primitive evolutionary state.

In cnidaria, we start to see the first signs of genuine nerve cells but they appear to be late-comers to an already established neuroid conduction pathway between different cell populations in these rudimentary radial organisms.

The capacity of neuroid conducting tissues to both rapidly sense and transmit environmental influences across entire populations of cells within the organism, positions them ideally for the evolutionary transition to the cellular architecture of nervous system tissues. By the time we get to advanced cnidarians, they exhibit full-fledged bidirectionally propagating radial nerve nets of considerable cognitive capacity. The transition to Bilateria will condense the nerve-net into a centralized unidirectionally propagating nervous system with afferent and efferent pathways. In addition to conducting influences and responses across the body, the neuroid tissues of early animals mediate the first indications of a generalized cognition in our pre-neural ancestors.