Neural control of urination - micturition reflex. When the bladder is full, stretch receptors in the wall of the bladder send nerve impulses to the sacral region of the spinal cord. By way of a parasympathetic response, signals return to the bladder and stimulate contraction of the muscle of the bladder and relaxation of the internal urethral sphincter.
This part of the reflex is involuntary and is predominant in infants and young children. As the central nervous system matures, it acquires voluntary control over the external urethral sphincter. Urination is controlled mainly by the micturition center in the pons.
This center receives sensory signals from the bladder and communicates with the cortex about the appropriateness of urinating at the moment. At times when it’s not convenient to urinate, the center sends back an inhibitory signal to keep the sphincters closed and prevent voiding. When you wish to urinate, this inhibition is removed; the spinal cord instructs the muscle of the bladder to contract and the sphincters to open to let the urine out.
