Physiology: Animal Function and Reproduction

Nervous System

How does the nervous system of invertebrates differ from that of vertebrates?

The least complex nervous system is the nerve net of cnidarians—a network of neurons located throughout the radial symmetrical body of organisms such as hydras (animals that lack a head and a brain). The neurons are in contact with one another and with muscle fibers within epidermal cells. Invertebrates that display bilateral symmetry— such as planarians, annelids, and arthropods—all have a brain (a concentration of neurons at the anterior or head end), one or more nerve cords, and the presence of a central nervous system. In contrast, vertebrates all have a central nervous system and a peripheral nervous system.

The nerve cell is a specialized cell that is capable of relaying electrical signals from various parts of the body to the brain.


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