A network of nerve cells connected with each other by chemical or electrical synapses. Characteristically, stimulation at any point in the net spreads in all directions, although some have fast, through-conducting pathways. The nervous system of certain invertebrates (e.g. cnidarians and echinoderms) consists exclusively of several overlapping nerve nets in the body wall. These show differentiation and adaptation depending on the part of the body and functions they serve. Sensory and motor functions often reside in distinct nets. Some other invertebrates (e.g. flatworms) have nerve nets that connect to the central nerve cords.