How Sperm Works

Sperm do not start swimming from the moment of ejaculation - they have only limited resources, and to stand much chance of reaching the egg, they need to delay their frantic dash until they are closer to the egg.
Scientists discovered that tiny pores on the sperm's surface allow it to change its internal pH, which in turn starts its tail movements. These pores, or Hv1 proton channels, as they have been termed, seem to be primed to open at precisely the right moment. They respond to a substance called anandamide, which is present in the female reproductive tract, and in particularly high levels near the egg.
The human body doesn't stop to amaze me.
[source:bbc.co.uk]