The scrotum is a unique structure as it has very thin, loose skin that is slightly hair bearing. It is controlled by the endocrine system and functions as a receptacle for the testes. This keeps the testicles outside the body, producing a cooler environment and thus providing the ideal area for the creation of sperm. Warmth tends to prevent sperm from developing properly. Underlying the skin of the scrotum is the cremasteric muscle, this muscle is incorporated onto the scrotum and by contracting it elevates the testicle. This is done in response to cool and warm weather and noxious or painful stimuli.
The testicles are roughly the sizes of a small egg; they are responsible for the development of sperm as well as the manufacture of the hormone testosterone. Behind the testicles sits the epididymis, a single coiled tube that is the site of sperm storage and maturation. The end of the epididymis results in a thick muscular tube called the vas deferens, which carries sperm from the epididymis to the prostate to be ejaculated. The sperm is carried in the vas deferens to the two structures that sit behind the prostate.
These structures are called the seminal vessels, glands roughly 5 cm in size that form a secretion which nourishes the sperm which also attaches to the prostrate. The prostate sits at the base of the bladder and creates a fluid that allows nourishment and activation of the sperm. The main purpose of both seminal vessels and the prostate is to provide nourishment and a place for sperm to live till ejaculation. The prostate secretes the majority of the fluid.
The creation of an erection is an extremely complicated cascade of events that require several different things to happen. There are a number of chemical transmitters involved in this including prostaglandins, nitric oxide, acetylcholine and epinephrine. The exact mechanisms by which the erection occurs is still unclear, but the neutral input from the brain is extremely important if this is to take place. Reflex erections usually experienced by paraplegics or people who have sustained cord damage, are often poor erections and not sustainable for prolonged periods of intercourse.
An erection occurs when the nervous system activates a rapid increase in blood flow. The vascular muscle becomes engorged with blood and the outflow of blood is cut off. An erection can occur as a reflex as seen in spinal patients, or can be psychogenic (originating in the mind) stimulation. A number of sexual stimuli are processed by the brain and transmitted to the penis via the nervous system. In order to increase the size of the erection there must be an increase of blood flow, at the same time this blood must be prevented from leaving the penis.
