What causes the inability to control urine (bed wetting) in elderly especially at night?

Weaker pelvic muscle: Weaker internal & external urinary spincters. Increase in women after multiple childbirth and men with large prostates. Also nervous system may be less responsive with age, especially the bladder control mechanism in the brain. Can be affected by reduced blood flow to certain ares of brain & advancing senility. Also ? Kidneys less able to reabsorb urinary water after filtration from blood.