As the bladder fills, stretch receptors trigger the urge to urinate — but you can override it, at least for a while. Fill the bladder and void it.
Bladder filling
Micturitionfill → urge → void
What's happening
The reflex: stretch receptors → spinal cord → the detrusor muscle contracts and the internal sphincter relaxes. The external sphincter is under voluntary control — which is how you “hold it.”
📷 Reference image
A real labeled figure to compare with the interactive above.
The Micturition Reflex — OpenStax, CC BY 3.0 (via Wikimedia Commons)
