Anatomy and physiology of the lower urinary tract.

The lower urinary tract has two main functions: storage and periodic elimination of urine. These functions are regulated by a complex neural control system located in the brain and spinal cord. This control system performs like a simple switching circuit to maintain a reciprocal relation between the reservoir (bladder) and outlet (urethra and urethral sphincter) components of the urinary tract. Spinal cord injury disrupts voluntary control and the normal reflex pathways that coordinate bladder and sphincter function. Studies in animals indicate that recovery of bladder function after spinal injury is dependent on the reorganization of reflex pathways in both the peripheral and the central nervous system. Part of this reorganization may be influenced by neural-target organ interactions that are mediated by neurotrophic factors released by the peripheral organs.