The document summarizes the process of micturition (urination). It describes how urine is transported from the kidneys to the urinary bladder via ureters. As the bladder fills, stretch receptors send signals to the brain and spinal cord. When the bladder reaches capacity, the micturition reflex is triggered to relax the internal urethral sphincter and contract the detrusor muscle in the bladder wall to empty urine from the bladder through the urethra. Both voluntary and involuntary neural pathways in the brain, brainstem and spinal cord coordinate the filling and emptying of the bladder.