Afferent nerve endings in the bladder wall are important in conveying the sensations associated with degrees of bladder fullness and also bladder pain to the spinal cord. This chapter discusses the peripheral control of micturition, cellular signaling pathways in normal bladder function, spinal control of bladder function, and interoceptive sensations. Acetylcholine (ACh) and adenosine triphosphate (ATP) are released by the bladder urothelium during urine storage, in increasing concentrations as the bladder wall distends. Muscarinic, nicotinic and purinergic receptors have been identified in the bladder urothelium and/or suburothelium in human or animal studies. In normal adults information about the bladder is passed from the periaqueductal gray (PAG) to higher regions of the brain. This type of interoception is mediated by afferent input through small-diameter fibers in lamina 1 of the spinal cord. A number of spinal reflex mechanisms are involved in the control of the urethro-vesical unit.