Nipple stimulation can activate the same brain area as genital stimulation in some people. Brain scans showed that when nipples are stimulated, the genital sensory cortex can light up.
An erection is a vascular process where the corpora cavernosa fill with blood, increasing in length and thickness, often initiated by the parasympathetic nervous system.
Gonadal hormones like testosterone and estrogen play a major role in activating and maintaining libido (sexual desire) in both men and women. The influence of these hormones changes with age, and central (brain) factors become more important over time.
Every two minutes, we take more pictures than all humankind did in the entirety of the 1800s. (Bonus fact: Photography was invented in 1826, that's 200 years ago this year!)
The vaginal canal has a collapsed, folded structure (rugae) that expands when aroused or during childbirth. These folds increase elasticity and surface area.
Even dim light at night can suppress sleep hormones
Exposure to very low levels of light (~30 lux for 1 hour) can significantly suppress melatonin production, making it harder to sleep.
