"The autonomic nervous system has two components: the parasympathetic and sympathetic nervous systems. The sympathetic nervous system prepares the body for the flight-or-fight response and accelerates the body. The parasympathetic nervous system brings the body to rest. The penis is the exception. **It is the parasympathetic nervous system that brings about an erection, whereas the flight-or-fight response makes the penis go limp** – for example, if a policeman turns up when two people are having sex in the bushes. The parasympathetic nervous system doesn’t need the brain in order to do its work. Look at patients with a serious spinal cord injury: not a single signal reaches the lower body from the head and yet local stimuli can trigger an erection, although they don’t feel it because sensations take place in the head." ([Location 1198](https://readwise.io/to_kindle?action=open&asin=B089QJDCV4&location=1198)) --- **Tags** -- [[quotes]], [[nervous-system]], [[human-biology]], **Source** -- [[20250426112058 - B - Members Club]]