urination

urination, the process of excreting urine from the urinary bladder. Nerve centres for the control of urination are located in the spinal cord, the brainstem, and the cerebral cortex (the outer substance of the large upper portion of the brain). Both involuntary and voluntary muscles are involved. The urinary bladder is a storage reservoir for urine—a liquid containing waste products given off by the body and extracted from the bloodstream by the kidneys. The major...