The detrusor smooth muscle generates spontaneous non-voiding contractile activity during the filling phase of the micturition cycle. An increase in this spontaneous activity may cause overactivity of the detrusor and symptoms associated with bladder overactivity which is a common problem and can seriously affect patients' quality of life. In the physiological bladder, spontaneous activity of the detrusor is modulated by ion channels in its myocytes as well as those present in nerves, the urothelium, and interstitial cells within the bladder wall. Thus, these ion channels are potential targets for treating overactive bladder syndrome. This short review discusses what is known about the spontaneous activity of the detrusor and implications in the pathophysiology of overactive bladder syndrome.