The Evolved History

The Nervous System Evolved

The nervous system is the primary means by which cells in the body communicate with one another. The endocrine system is adjacent to this, but is not synonymous—though it’s not going to be covered anywhere here.

By using the nervous system, different parts of an organism can coordinate to perform intricate tasks. Systems vary in complexity from simple cell-to-cell communication, which is arguably not a true “system”, to vast networks of specialized nerve cells, each with its own dedicated purpose.

In short, it allows different areas of the body to collaborate for tasks such as movement and thought.

Porifera, known colloquially as the sea sponges, are composed of a diverse phylum of aquatic animals. They are also the host of the simplest form of nervous communication: cell-to-cell, sometimes called intercellular signalling.

An example of Porifera. "Aphrocallistes vastus" | by Dan Hershman from Wikimedia Commons | Licensed under CC BY-SA 2.0

Cell-to-Cell Communication

Cell-to-cell is not typically considered to be a nervous "system", as there is no level of organization to it, but rather a nervous function. This function is not unique to Porifera, but they are unique in being the only animals whose cells send signals by this method alone.

A diagram of cell-to-cell type communication.

With intercellular signalling, there are sensory proteins that penetrate the cell membrane and come into contact with other cells. There are also proteins on the inside of cells that detect chemicals, such as ligands, almost like a rudimentary endocrine system. These signals provide valuable insights, including information about water current activity, light levels, and what types of cells are nearby.

Even an apparently simple, crude function like intercellular signaling is essential in allowing eukaryotic organisms to coordinate actions.