These are one of the funniest kind of jokes because the Medical profession is otherwise a serious profession.
A female brain cell was lost one day, and found itself inside a man’s head.

Looking around, she saw that it was all very dark and empty. She started to get a little afraid, so she called out nervously, “Is anyone here?” With the only thing coming back to her being was the echo of her own voice; she called a little louder, “Can anyone hear me?” Still there was no response.

By now the female brain cell was quite frightened and she called out loudly again, “IS THERE ANYONE HERE!”

From far away she heard a little voice reply, “Hello hello, we are all down here…”

:D :)