Medical/Psychological basis for horniness

Based somewhat on the recent masturbation thread, I’ve been wondering about the nature of horniness.

Is there a physiological basis behind being horny? Is it related to something like the build-up of fluids needing released or is it a purely psychological phenomenon?

While I’m wondering, what about the actual sensation of being horny? To me it’s like a subtle pressure - not entirely unlike the pressure felt when you have to go to the bathroom. Is this, again, a psychological thing or is there some sort of physical change that I’m sensing (increased blood flow or similar).

i don’t know the neurology of horniness but certain drugs like weak androgenic anabolic steroids or SSRI anti depression meds can greatly cut down someone’s sex drive.