Nerves - Organisation of Nervous System

Due to the pattern of distribution of neurons as described above, there are bundles of nerve fibers, called nerves, connecting the central ganglia on the one hand, and sensory neurons or the effector organs on the other.

Figure: A drawing of the neuronal organization in a primitive worm with a central nervous system.

The nerves may consist of sensory, motor or both types of fibers, and depending on this the nerves may be sensory, motor or mixed correspondingly. Likewise, there are connectives running between ganglia of the same side, and commissures among the ganglia of the opposite side. They mostly consist of association fibers.