I googled and read about the kidneys, bladder, and urethra but no source explains the dynamic process.
From my own personal experience, the process has four stages:
The muscles are in normal mode. Then, a feeling comes that you need to empty the bladder.
The muscles are relaxed so the flow starts.
After the last drop, the muscles are contracted and this time a short flow happens (much fewer amount of urine comes out).
Muscles go back to normal mode.
I would like to ask specifically about stage 3. Why does the last amount of urine come out this way? Why doesn't it simply go out with the rest of the urine? What's the responsible muscle?