To pee or not to pee: How the brain controls the bladder

September 23rd, 2025

Written by: Andrew Nguyen

Everyone knows the urgent feeling of a full bladder and the need to act on it quickly, but how does a full bladder turn into the feeling that you need to go? Inside the human body, our organs are constantly filling, pumping, and squeezing to perform their functions. Much like our external senses allow us to see, hear, smell, taste, and feel, the sixth sense of interoception allows us to detect what is going on inside our body. The urge to urinate is one of these interoceptive signals, essential for maintaining fluid balance and eliminating waste. While the experience feels straightforward, the underlying neural mechanism is surprisingly complex and has only recently become a focus of neuroscience research, but is already turning up exciting results. 

Holding It In

As the bladder fills, neurons that connect the bladder and spinal cord start to communicate more strongly. These neurons help keep urine stored in the bladder by contracting internal sphincter muscles in the urethra and relaxing bladder muscles. This is a passive process that the body does without conscious thought. As the bladder fills, you can also consciously choose to hold it in. This happens through the neurons that go from the brain back down to the bladder that activate external sphincter muscles in the urethra to try and prevent anything from leaking out. While you choose to hold it in, neurons from the bladder are sensing information about how full the bladder is and communicating to the brain, leading to the increasing urge to urinate. However, choosing to hold it in eventually becomes painfully hard for the brain to do and is forced to switch modes to start peeing. 

Let it Flow

Once the bladder is full and you can’t hold it in any longer, your brain tells the body to start preparing to release the pee. During this transition, neurons sense the bladder expanding and communicate that information through the spinal cord to an area at the base of the brain called the periaqueductal gray (PAG). The PAG receives this urgent message and sends signals up the brain to an area called the cortex. Once you decide to start peeing and let it flow, these cortical regions signal back down the body and tell the muscles in the urethra to relax and the muscles around the bladder to squeeze– emptying the pee at a smooth, constant flow and giving you that sweet sense of relief. This complex brain-bladder conversation is how the body signals the increasing drive to pee to the brain and how the brain can decide whether to hold it in or let it flow¹. 

Pee Shyness: Context Matters

The timing of urination is not just wherever, whenever– it depends on the context. Many animals use pee for communication, such as marking territory or signaling social rank. In mice, dominant males tend to pee over a large area in an attempt to spread their odor and signal their social rank. Meanwhile, females and subordinate males restrict peeing to specific areas, potentially because it is the safest spot to go. You can imagine that animals might want to strategically pee where it is safest and where they can attract a partner. On the other hand, humans also decide when and where to pee based on complex social contexts. Societies have developed bathrooms as a socially appropriate environment to pee, but others know to pee in hidden outdoor areas when needed.

One group of researchers identified complex “pee” or “don’t pee” cues that signal to neurons in an area of the brain called the pontine micturation center (PMC). When these PMC neurons are inactive, this social hierarchy of peeing behaviors goes away². Once the decision is made that it is an appropriate time and place to pee, a number of different regions in the brain send a coordinated message to the PMC to start squeezing the bladder. In this way, the PMC is an important hub for integrating many different signals from the environment to decide when and where it is appropriate to pee.

Some Pee Takeaways

Peeing is more than just a passive action, it’s a complicated brain-bladder conversation. Neurons in the body sense the bladder stretching while the spinal cord and brainstem try to monitor how full the bladder is and communicate between the brain and bladder to control when to hold it in and when to pee. This also all depends on the right environment! For most people, this system works automatically, but under conditions like urinary tract infections, loss of bladder control throughout aging, or neurological disease, the circuitry can malfunction. Studying the neural control of peeing not only demystifies this universal process but also points toward new treatments when this essential function goes awry. Now we are starting to get a look under the hood of how this simple question– to pee or not to pee– is much more complicated than it seems.

References

1. de Groat WC, Griffiths D, Yoshimura N. Neural control of the lower urinary tract. Compr Physiol. 2015 Jan;5(1):327-96. doi: 10.1002/cphy.c130056. PMID: 25589273; PMCID: PMC4480926.
2. Hou XH, Hyun M, Taranda J, Huang KW, Todd E, Feng D, Atwater E, Croney D, Zeidel ML, Osten P, Sabatini BL. Central Control Circuit for Context-Dependent Micturition. Cell. 2016 Sep 22;167(1):73-86.e12. doi: 10.1016/j.cell.2016.08.073. PMID: 27662084; PMCID: PMC6217838.
3. Tadic SD, Holstege G, Griffiths DJ. The CNS and bladder dysfunction. F1000 Med Rep. 2012;4:20. doi: 10.3410/M4-20. Epub 2012 Oct 2. PMID: 23091564; PMCID: PMC3470460.

Cover Photo by Zorro4 on Pixabay