As arthropods (Phylum Arthropoda), ladybugs have ventral nervous systems. Their nervous system is divided into the brain, which is located at the anterior end, and the ventral nerve cord spanning from the head to the caudal end, the abdomen.

 

According to Encyclopaedia Britannica, the arthropod nervous system consists of a dorsal brain and a ventral, ganglionated longitudinal nerve cord (primitively paired) from which lateral nerves extend in each segment. The system is similar to that of annelid worms, from which arthropods may have evolved. The neuromuscular organization of arthropods is quite different from that of vertebrates, in which one neuron supplies a number of muscle cells, together forming a functional motor unit. The small size of the muscles prohibits such an organization in arthropods. Instead, the state of contraction of an arthropod muscle is determined by which of several different types of neurons supplying one muscle cell are fired.

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The sense organs (sensilla) on the body surface involve some specialization of the exoskeleton barrier. The sensory nerve endings are lodged in cuticular hairs (setae), peglike projections, cones, pits, or slits, which may occur in large numbers on antennae, mouthparts, joints, and leg tips. Changes in the tension of the surrounding cuticle stimulate the nerve endings. Tension changes in the exoskeleton cause slight movements in the cuticular membrane and stimulate the receptors. Slits of varying length may be grouped together like the strings of a harp.

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The ventral nerve cord is connected to the brain by the circumesophageal connectives. It is composed of a double row of ganglia connected longitudinally by connectives and transversely by commissures. 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.

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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.