How does the bladder work?

But what does the bladder even look like? You can imagine it like a hollow balloon-shaped muscle that sits in your pelvis. As it fills up, the urine flows into the bladder and it expands until your body notifies you that it’s time for a pee. Once the bladder has been emptied, it will flatten down and sit as a hollow balloon in your pelvis again. It’s primary jobs are to store and release urine that flows from the kidneys into the bladder. Now wouldn’t it be nice if all our jobs were this easy?

The bladder and the urinary system

How does this whole thing work? Well, let’s start at the top. The urine is produced in our kidneys, which sit in the upper urinary tract just below your ribcage. As the urine is produced it flows from A to B – kidneys to bladder – via long tubes called ureters. At the end of these tubes sits the bladder. The bladder belongs to the lower urinary tract and shares a space with the urethral sphincters (the muscles that control whether you’re releasing urine or holding on to it) and the urethra (the tube that is also the exit route for the urine from your body). As the urine reaches the bladder, it is stored there until it’s time for you to go for a pee. Generally, you’ll feel the urge when your bladder is about half full. Once you’re sat on the toilet, the pelvic floor muscles and sphincters relax, the bladder contracts, and the urine leaves the body via the urethra.

The bladder and the brain

Although these two couldn’t be any further apart, they’re closely connected as all bladder activity is regulated by the brain. Usually, the brain will send messages through the nerves in the spinal cord right to your bladder. That’s how it knows if it’s appropriate to pee or if it should hold on to the urine for a little longer. Sounds a little confusing, right? Well, let’s look at an example. If you feel the need to urinate, your brain will assess the situation and, if you’re not sitting on the toilet, tell your urethral sphincters to squeeze and the pelvic floor to lift to keep the urine inside the body. It will only tell the muscles to relax and the bladder to contract once you’re in a situation where peeing is appropriate – like the toilet.

As you can see, the relationship between bladder and brain is quite important. But how does the brain even know that the bladder is getting full? The bladder wall is made of a net of muscles with stretch receptors. As the bladder fills, the receptors will send signals through the nerves in the spinal cord to the brain. The brain then knows that it’s slowly time to go for a pee. It’s quite apparent just how many parts are at play that need to work together without problems for the bladder to function properly.

Neurogenic bladder

If the relationship between bladder and brain is disrupted, you are experiencing something called a neurogenic bladder. This means that the nerves in the spinal cord, responsible for sending messages back & forth between brain and bladder, are damaged. The damage can occur either through injury or illness and generally leaves you in a position, where you are no longer able to control your bladder function.

With a neurogenic bladder, it is possible that you’re either unable to empty your bladder or that you are experiencing involuntary leakage. In some cases, both can happen. Depending on where in your spinal cord the nerves are damaged, you will either experience an overactive or an underactive bladder. Your bladder will generally be overactive if the lesion is above the T12 vertebrae and an underactive bladder if it’s below.

Overactive bladder: You may feel the need to pee, even if your bladder isn’t full. The urge to go to the toilet can come on so fast that you can’t make it to the bathroom in time. This is especially true when you’re injured or living with a disability.
Underactive (flaccid) bladder: You may not get the signal that it’s time to pee or the sphincter muscles may be too tight for urine to exit the body – also called an obstructive bladder. The second scenario can cause overflow incontinence if the bladder becomes too full.

To diagnose a neurogenic bladder, a doctor will conduct several tests of your bladder, spinal cord, and brain and will also review your health history. A physical exam is generally also part of the diagnosis, as a loss or change of sensation to your lower limbs can be a sign that you have some sort of nerve damage.

The role of the spinal cord

The spinal cord could be described as the channel of communication for the messages that get sent between the bladder and the brain. The nerves in the spinal cord are usually transmitting these signals. So when they become compressed, injured, or – worst case – permanently damaged, bladder problems will occur. If this is the case, then you are suffering from a neurogenic bladder.