It’s an amusing, albeit often highly inconvenient, phenomenon that half of the world’s population has to deal with on a regular basis. So what’s the science story behind that morning glory? Let’s find out.
Morning glories, or nocturnal penile tumescence (NPT) as they are correctly called, are spontaneous er3ct1ons that occur during sleep or while waking up. All blokes without er3ct1le dysfunction are graced with them and they normally occur around three to five times during sleep.

NPT actually starts in utero, or in the womb (seriously), and continues throughout life. If it’s any consolation, men aren’t completely alone—women also get clitoral er3ct1ons and vaginal engorgement during sleep, and various nonhuman mammals also get NPT. While a few different theories have been proposed over the years to explain NPT, what causes it still remains uncertain. NPT, just like clitoral er3ct1ons, is associated with REM (rapid eye movement) sleep. One idea is that during REM sleep, noradrenergic cells (neurons that release the neurotransmitter noradrenaline [norepinephrine]) located in an area of the pons (part of the brainstem) called the locus coeruleus are switched off. It is thought that these cells are associated with the inhibitory tone of the p3n1s; therefore, when their activity is reduced during REM sleep, testosterone-dependent excitatory tones can be expressed which result in an er3ct1on.

It’s also been suggested that NPT is triggered by the release of nitric oxide (NO). NO is released by cells that line the inside of blood vessels which then diffuses into smooth muscle, causing it to relax. This also causes blood vessels to dilate, hence increasing blood flow to the p3n1s and voila, an er3ct1on. It’s thought that increased activity of part of the pons during REM sleep triggers a cascade of events that ultimately lead to NO release by nerve fibers. This is also regulated by androgens such as testosterone.


SOURCE: http://hottestdaniel..com/2015/06/why-do-men-get-erections-in-morning.html