The visceral (or autonomic) motor system controls involuntary functions mediated by the activity of smooth muscle fibers, cardiac muscle fibers, and glands. The system comprises two major divisions, the sympathetic and parasympathetic subsystems (the specialized innervation of the gut provides a further semi-independent component and is usually referred to as the enteric nervous system). Although these divisions are always active at some level, the sympathetic system mobilizes the body's resources for dealing with challenges of one sort or another. Conversely, parasympathetic system activity predominates during states of relative quiescence, so that energy sources previously expended can be restored. This continuous neural regulation of the expenditure and replenishment of the body's resources contributes importantly to the overall physiological balance of bodily functions called homeostasis. Whereas the major controlling centers for somatic motor activity are the primary and secondary motor cortices in the frontal lobes and a variety of related brainstem nuclei, the major locus of central control in the visceral motor system is the hypothalamus and the complex (and ill-defined) circuitry that it controls in the brainstem tegmentum and spinal cord. The status of both divisions of the visceral motor system is modulated by descending pathways from these centers to preganglionic neurons in the brainstem and spinal cord, which in turn determine the activity of the primary visceral motor neurons in autonomic ganglia. The autonomic regulation of several organ systems of particular importance in clinical practice (including cardiovascular function, control of the bladder, and the governance of the reproductive organs) is considered in more detail as specific examples of visceral motor control.