Nitric oxide stimulates the endothelium to secrete nitric oxide, which causes vasodilation and increases blood vessel diameter, leading to erection.

“and you can get stimulation oral I mean excuse me ocular Vision hearing sensory any kind of sensory stimuli or tactile can induce the nerves to secrete nitric oxide which will then go to the endothelium this is the key the endothelium will secrete nitric oxide which is really the on off switch once the nitric oxide goes up we get an increase in something called cyclic GMP cyclic GMP causes intracellular calcium to go down it causes the dilation of the sinusoids and increases the blood vessel diameter and the blood comes in”