Male Nervous System
The male nervous system consists of the brain, spinal cord, and a variety of nerves found throughout the body - mainly in the pelvis and on the genitals. Testosterone can have the effect of "sexualizing" the brain thus increasing libido (sexual desire). However, the majority of the sexual functions in men reside in the spinal cord.
Erections, especially ejaculation, are not directly conscious decisions but are controlled by reflexes. For example, it is difficult for men to consciously decide to get an erection--he has to be triggered either mentally or physically to get an erection by reflex. Sure he can think sexual thoughts or choose to engage in physical stimulation in order to get an erection,but getting an erection is not as easy as lifting his finger and pointing it in the direction he wants. Likewise, ejaculation is not a conscious decision like urination. Rather, a man can increase or decrease sexual stimulation in order to trigger the reflexes that will eventually cause him to ejaculate. This reflex system can often be an annoyance to some men. They may reflexively get an erection when they don’t want one, or the reflexes to ejaculate may seem to work either too quickly or too slowly during sexual activity. All of this is controlled by the male nervous system.
The male reproductive system is attached to a network of nerves. These nerves come off the spinal cord and extend to the male sexual organs and glands (see image below) and control everything from erections to ejaculation.
SPINAL NERVES & REFLEXES
The nerves coming off the spine between vertebrae T11 and L2 (upper small of the back) are responsible for erections caused by psychogenic stimuli from the brain (images, smells, anticipation for sex, memories, etc.). During ejaculation the nerves from this area are also responsible for the first phase of ejaculation called emission, which involves contraction of the sexual glands to create semen and depositing that semen into the urethra at the base of the penis. The nerves coming off the spine between vertebrae S2-S4 (under the buttocks) is the area of the spine responsible for erections caused by physical stimulation (penis and scrotal stimulation). The nerves in this area are also involved in the second phase of ejaculation called expulsion, where semen is propelled out of the penis (click HERE to learn more).
Since two areas of the spine trigger erections, it is possible for a man to get an erection for one or more reasons – mental stimulation and/or physical stimulation.
However, ejaculation is an event that requires these two areas of spinal nerves work in coordinating the two-step process of ejaculation (emission followed by
expulsion). An area of the spine between these two ejaculation zones is located between vertebrae L3-L5 (in the lower small of the back) and is called the spinal
ejaculation generator or SEG. The SEG gathers input from sexual stimulation (mental and physical); and when sexual stimulation reaches a certain threshold, the SEG coordinates the entire process of ejaculation.[i]
A plexus of nerves (basically a complex network of nerves that looks somewhat like a net) sits in the pelvis and is called the pelvic plexus. The pelvic plexus is responsible for erectile function and sexual stimulation. Nerves from the pelvic plexus cradle the prostate and are sensitive to and can become compressed when the prostate gland swells to fullness with sexual fluid (which can help trigger wet dreams when reproductive glands are full).
The pudendal nerve branches off the pelvic plexus and extends down onto the penis (Penile Dorsal Nerve) and rear side of the scrotum (Posterior Scrotal Nerves). Nerves then lead back from the pelvic plexus to the erection and ejaculation centers of the spine. Small amounts of physical stimulation of the pudendal nerve on the penis or scrotum will trigger the pelvic plexus to send a signal to an area of the spine around S2 to cause an erection. Continued stimulation of this pudendal nerve fires up the spine to result in ejaculation.
Although nerves fire signals electrically, they communicate with one another through neurotransmitters or chemicals. This occurs mostly in the brain, but can also occur between nerves in the spine and pelvic plexus.
Three main chemicals are worthy of note:
First is dopamine. I call dopamine the “fun uncle.” It is involved in reward and pleasure. In men it is a sexual enhancer by promoting sexual drive and in bringing him to orgasm faster.
The second neurotransmitter is norepinephrine, which I call the “dad” because it’s a little bit of a kick in the butt. It is the chemical signal involved in the fight and flight response and increases heart rate and constricts blood vessels. This is released in anticipation of sexual activity (the excitement and rapid heartbeat).
The third neurotransmitter is serotonin, which I call the “mom”. It stabilizes the nervous system, gives the individual a sense of well-being, calmness, and sedation. In addition, serotonin is sexually inhibiting and can reduce libido, inhibit the ability to attain or maintain an erection, and even delay or prevent ejaculation.
Imbalances in these neurotransmitters within certain parts of the brain can lead to depression and anxiety. To learn more about depression/anxiety, click HERE.
AUTONOMIC NERVOUS SYSTEM
The process of sexual stimulation is actually very unique when we talk about the autonomic nervous system, which is basically the part of the nervous system that handles automatic functions. Most automatic functions in the body are controlled by one of two branches of the autonomic nervous system – either the sympathetic (fight and flight) or the parasympathetic (rest and digest) systems. For example, if you were to come upon a bear and it started chasing you, your sympathetic nervous system would kick into gear automatically. Your airways would open, your heart rate would increase, your bladder would snap shut so you don’t leave a scent trail, etc. All of this would occur automatically without you having to consciously think about any of it. On the other hand; if you just ate a large meal, your parasympathetic nervous system would slow down your heart rate, cause you to relax, etc. This is the reason we often feel “lazy” or “chilled out” after eating a big meal. Sexual activity in men is the main time when these two nervous systems have to coordinate with one another.
The parasympathetic nervous system (the rest and digest portion) controls erections. This makes sense to most guys – they typically have to be pretty chilled out and not necessarily all keyed up or frightened. In fact, one of the main reasons men lose an erection when they don’t want to is when they get “stage fright”. This stage fright can occur during sexual activity when they stress out about not being able to get or maintain an erection, or if they are sexually active with their spouse and hear a noise that may make them concerned that someone may walk in on them or be within ear shot. This can cause a man to lose an erection almost immediately. In fact, stage fright or being all keyed up is one of the leading causes of erectile dysfunction.
The sympathetic nervous system (the fight and flight portion) actually controls ejaculation. This makes sense as well as ejaculation is a highly stimulating event that causes the heart to beat rapidly and the moments leading up to and during ejaculation are high intensity events for men to experience. In fact, one of the only times men will ejaculate when they are not sexually stimulated is in highly traumatic events. There have been multiple reports of men ejaculating during a car crash or other stressful event. This is because the hormones released during fight and flight are the same hormones that are triggered when you’re running from a bear. The sympathetic nervous system causes people to feel keyed up and may be one reason why men desire to engage sexually after having had a hard day at work or because they are completely stressed out. It also explains why stress is a major trigger for masturbation in men struggling with masturbation and/or pornography addictions. These stressors often prime the male reproductive system to lean towards ejaculation. Lastly, this can also explain why many men can have high stress dreams when they have wet dreams. We most often think about wet dreams being triggered by sexual dreams, but many men report having non-sexual dreams of high stress situations causing wet dreams (being late for class, getting fired from a job, etc.). These high stress dreams trigger the fight and flight (sympathetic nervous system) during sleep thus promoting ejaculation to occur.
[i] Chehensee C, et. al., Annals of Neurology, 81:1, Human Spinal Ejaculation Generator, January 2017, 35-45. http://onlinelibrary.wiley.com/doi/10.1002/ana.24819/abstract (7/4/17)
Images on this page from top to bottom include: