– parasympathetic fibers reach the detrusor muscle via the pelvic nerve[S2 through S4].

-Detrusor muscle contraction is caused by parasympathetic Ach activation of M3 receptors.  

-Sympathetic fibers reach the detrusor muscle via the hypogastric nerve[lower thoracic and upper lumbar segments].

-Sympathetic inhibition of detrusor is via NE activating &beta receptors.

-Onuf nucleus exists at S2 and S3 and provides somatic motor innervation to the external sphincter via the pudendal nerve. This sphincter contracts via sympathetic NE interaction with alpha1 receptors to prevent urination, and relaxes via nitric oxide signaling to allow urination