The other complex compartmentalized nervous system is found in arthropods (see the diagram).
The arthropodan brain consists of three main regions: the protocerebrum,deutocerebrum, and tritocerebrum. The anterior protocerebrum, which receives the nerves of the eyes and other organs, contains centres, or neuropils, such as the optic centres and bodies known as corpora pedunculata. The neuropils function as integrative systems for the anterior sense organs, especially the eyes, and in control of movement; they also are the centres for the initiation of complex behaviour. The deutocerebrum contains the association centres for the first antennae. The posterior tritocerebrum contains association neuropils for the second antennae (of crustaceans) and gives rise to nerves that innervate the mouthparts and the anterior digestive canal. The latter constitute the stomatogastric system, which regulates the intake of food and the movement of the gut necessary for digestion. This system bears a resemblance to the vertebrate autonomic system. The ventral nerve cord, connected to the brain by the circumesophageal connectives, is composed of a double row of ganglia connected longitudinally by connectives and transversely by commissures. Different groups of arthropods exhibit different degrees of fusion of the ganglia. In insects the first ganglion, the subesophageal, is formed by fusion of three pairs of ganglia; it sends nerves to the mouthparts and to the salivary glands. The segmental ganglia in the thorax and abdomen provide nerves to the appendages, dorsal muscles, sense organs, and heart. Insects have 3 pairs of thoracic ganglia and up to 10 abdominal ganglia. The most common sensory receptors in arthropods are the cuticular hairs, many of which are mechanoreceptors, sensitive to touch, vibration, water currents, or sound waves; some hairs are chemoreceptors, which detect odours or chemicals in the water. Hairs situated near the joints are stimulated by...
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