What causes morning erections in men?!

What causes morning erections in men?!
Morning erections of the penis in men is the reflex erection occurs during sleep or when you wake up in the morning, and it is not something to worry about, this erection is proof you sound sexually may occur at bedtime six times or more when a healthy person, and in fact there are many reasons that cause morning erections in men:
Full bladder urine, is really an acceptable and reasonable assumption something because once you empty the bladder of urine after waking happens then relaxes in the erection of the penis.

But numerous studies have shown, research about the modern bedroom that erection-anniversary is often associated with REM during sleep the unconscious sex among young adults.
The morning erection is a supplement to the erection and completion of erection already mentioned and the University of Maryland researchers confirms that full bladder has nothing to do with the morning erections in young men and they had to wake a group of people before the rem phase, also called scientists, and then asked them to go back to sleep and found that while the bladder is not full of urine occurs if an erection.
But scientists did not know the exact reasons for this type of morning erections but there are some scientific theories that refer to a decrease in the rate of inhibition of brain centers of nerve endings causing erectile anniversary by certain nerves in the brain affected and the resulting increase in the secretion of certain substances that increase the supply of penis with more blood and strengthen the process of erection.
But there is no reason to fear the contrary morning erections when young men on sexual health and safety.