The bladder problems common to MS are a direct result of lesions in the central nervous system (CNS). The urinary system is made up of the:
The kidneys act as a filter. They remove the bad stuff, such as toxins from the blood stream. Once the impurities are removed from the blood they're excreted into the urine.
The ureters are the small tubes between the kidney and the bladder. Urine is transplanted through them to the bladder.
Your bladder holds the urine until it's time to void or urinate.
This is the single tube that transports the urine containing all of the bad stuff out of your body.
Now that you have the basics, lets talk about the actual process. When there are no problems with your bladder, several things have to happen at the same time.
The detrusor or bladder muscle has to contract to expel urine. At the same time the internal and external sphincters need to relax. Urine will then be able to pass freely out of your body.
When the urinary system is functioning normally urine is collected slowly. And the bladder slowly expands. When there is about 6-8 oz. of urine, the nerves kick in. Nerve endings inside your bladder send a message to the brain. "It's time to urinate."
The brain sends a message back to the spinal card. It signals the voiding reflex to contract the detrusor or bladder muscle and relax the urethral sphincter, allowing you to urinate.
This urinary symphony can only happen when the whole orchestra is playing and everyone is watching the conductor. At the very least, there are three things that can go wrong when you have MS.