sacral parasympathetic pathway controlling the sexual organs in both males and
females originates in the sacral segments S2–S4 and reaches the target
organs via the pelvic nerves. Activity of the postganglionic neurons in the relevant
parasympathetic ganglia causes dilation of penile or clitoral arteries, and a
corresponding relaxation of the smooth muscles of the venous (cavernous) sinusoids,
which leads to expansion of the sinusoidal spaces. As a result, the amount of blood
in the tissue is increased, leading to a sharp rise in the pressure and an expansion
of the cavernous spaces (i.e., erection).