Why We Wee When We Want – How The Brain Controls The Bladder

The Lord of the Rings: The Two Towers is a long film. I remember seriously regretting my decision to wash down my popcorn with a litre of diet coke when the film decided to taunt my aching bladder with a protracted scene of a dam breaking. When you feel such an urge to go to the toilet, it can be hard to focus on anything else, even the movie!

The bladder is unusual amongst internal organs in that it can be consciously controlled. While one cannot will the heart to beat faster or slower, or the pancreas to secrete more or less insulin, most people are able to defer the emptying of their bladder until a safe and socially acceptable time, even if this may cause great discomfort.

The sensation of ‘needing a wee’ occurs when the walls of the bladder are stretched. Nerve endings in the bladder wall detect this stretch, and send electrical messages to the brain. If this occurs at a time or place in which it is not socially acceptable to urinate (which is most of the time!), a ‘voiding circuit’ in the brainstem is consciously kept under control by higher brain regions.

If you decide that this is indeed a good time to empty the bladder, the ‘voiding circuit’ sends messages to allow passage of urine: first to the bladder to tell it to contract, and second to the urethral sphincter muscle to tell it to simultaneously relax. With a permission from the higher brain centre, a contracted bladder and relaxed urethra, we wee when we want.

It is unclear how exactly the brain controls urinary voiding. Which neurons in the brain ‘switch’ the bladder from storage mode into urination mode? How do they communicate with the rest of the voiding circuit? These questions are the focus of my research – finding the answers may point towards ways of helping people with an ‘overactive’ bladder.

Overactive bladder patients suffer from frequent intense urges to urinate and often, without prior warning, involuntarily leak urine (incontinence). These symptoms not only greatly impact the sufferer’s quality of life, but also come attached with a social stigma, leading to feelings of shame and embarrassment. Around 10% of the UK population are estimated to suffer from overactive bladder, and this number is likely to increase due to our aging population.With the management of incontinence currently estimated to consume over 1p out of every £1 spent on the NHS, we literally cannot afford to neglect this problem.

Researchers are beginning to understand the brain regions that are involved in bladder control. Animal experiments have shown that a brainstem region known as the Periaqueductal Grey (PAG) is essential to the control of voiding – it may be where the crucial ‘switch’ between bladder filling and voiding happens. Human studies confirm that PAG has a role in voiding control. Using fMRI scanners researchers have
shown more activity in the PAG region in the human brain when the bladder becomes full. Some recent experiments indicate that electrical deep brain stimulation of the PAG may help with continence.

With a better understanding of how the brain controls the bladder, and how these mechanisms malfunction, we may be able to develop more targeted and effective treatments for people with incontinence. I hope that my research will one day help more people to wee when they want.

About the author

Jonathan Crook - Getty Science

Jon Crook is a postdoctoral research assistant in the School of Physiology and Pharmacology at the University of Bristol. His current research project concerns the role of periaqueductal grey matter neurons in micturition control. He completed his PhD in neuroscience at the University of Bristol in 2014, and previously studied Biomedical Sciences at the University of Leeds. His interests include reading, running and rock music.

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