The arousal response is initiated by parasympathetic tone, shifting towards sympathetic nervous system activity as arousal progresses.

“However, the sexual arousal itself in both males and females is actually driven primarily by the parasympathetic arm of the autonomic nervous system. So while pursuit is one of alertness and sympathetic drive, as we say, again, sympathy is not really what's at play here, the word simple means together, and the activation of the autonomic nervous system toward more alert state is because of a sympathetic nervous system, meaning the co-activation together of many neurons in the brain and spinal cord. But then the actual physiological arousal state that we call sexual arousal is predominantly parasympathetically driven, okay?”