![]() ![]() It contains a brain, ventral nerve cord, and ganglia (clusters of connected neurons). The insect nervous system is more complex but also fairly decentralized. Flatworms of the phylum Platyhelminthes have both a central nervous system (CNS), made up of a small “brain” and two nerve cords, and a peripheral nervous system (PNS) containing a system of nerves that extend throughout the body. Others, like jellyfish, lack a true brain and instead have a system of separate but connected nerve cells (neurons) called a “nerve net.” Echinoderms such as sea stars have nerve cells that are bundled into fibers called nerves. Some organisms, like sea sponges, lack a true nervous system. Nervous systems throughout the animal kingdom vary in structure and complexity, as illustrated by the variety of animals shown in Figure 16.2. ![]() Compare the functions of different types of glial cells.List and describe the four main types of neurons.List and describe the functions of the structural components of a neuron.
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