Part of the AUTONOMIC NERVOUS SYSTEM. It consists of scattered collections of grey matter known as ganglia, united by an irregular network of nerve-fibres; those portions where the ganglia are placed most closely and where the network of fibres is especially dense being known as plexuses. The chief part of the sympathetic system consists of two ganglionated cords that run through the neck, chest, and abdomen, lying close in front of the spine. In conjunction with the other part of the autonomic nervous system – the parasympathetic – this part controls many of the body's involuntary activities involving glands, organs and other tissues. (For further details, see NERVOUS SYSTEM.)