An interactive Flash animated diagram, depicting bladder control in older children. The human body controls urination through a process called the micturition reflex, which has two parts: the simple arc reflex at the level of the spinal cord, where stretch receptors send a signal to let the CNS know when the bladder is becoming full, and a regulatory loop so the brain controls the contraction and relaxation of the external sphincter muscle. When the bladder is full, the spinal cord will respond with instructions for the detrusor muscle in the bladder to contract and the internal sphincter muscle to relax (to urinate), but in older children and adults, control over the external sphincter muscle means it will stay contracted until the brain decides it’s time. Click through an animated slideshow to examine the process of urination in older children.
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