Prostate Anatomy & Sexual Function
Zonal Anatomy, Seminal Emission, and the Neurovascular Bundles
Evidence grade 5 of 5, Settled. Read how the Atlas grades evidence.
The written rationale for this grade is still being prepared.
- FDA
- Not applicable (anatomical topic)
Reference only. Not medical advice.
This is something to take to a clinician. The Atlas can tell you what is known about prostate anatomy & sexual function in general. It cannot tell you what is happening in your body, and the difference matters most for exactly the symptoms that bring people to this page.
The prostate is a fibromuscular gland (~20 g in young men) encircling the urethra just below the bladder. McNeal's zonal model (1981) divides it into peripheral, central, transition, and anterior fibromuscular zones, clinically pivotal because cancer arises mostly in the peripheral zone while benign hyperplasia (BPH) arises in the transition zone. Its sexual relevance is threefold: it contributes ~20-30% of seminal fluid volume, its smooth muscle drives emission and the bladder-neck closure that prevents retrograde ejaculation, and the cavernous (erectile) nerves run in neurovascular bundles directly along its posterolateral surface, which is why prostate surgery so readily damages erectile function.
A walnut-sized gland sitting at the crossroads of urine, semen, and the nerves of erection.
What people take it for
What it is taken for. Approval, where it exists, covers only some of these.
How it works
During the emission phase of ejaculation, sympathetic stimulation contracts the prostatic and seminal-vesicle smooth muscle, expelling secretions into the prostatic urethra, while the bladder neck (internal urethral sphincter) closes to direct semen forward (antegrade). The expulsion phase then follows via rhythmic bulbospongiosus contraction. Prostatic fluid is alkaline and rich in zinc, citrate, and prostate-specific antigen (PSA), a protease that liquefies the coagulum and aids sperm motility. Erection itself is a parasympathetic/nitric-oxide event mediated by the cavernous nerves in the neurovascular bundles, anatomically separate from the gland but physically adherent to it.
McNeal described four regions: the peripheral zone (the bulk of glandular tissue, posterior, where most cancers begin and where the digital rectal exam palpates), the central zone (surrounding the ejaculatory ducts), the transition zone (periurethral, the site of BPH nodules), and the anterior fibromuscular stroma (non-glandular). The prostatic urethra runs through the gland; the verumontanum (seminal colliculus) is the landmark where the ejaculatory ducts and prostatic utricle open. The neurovascular bundles, carrying the cavernous nerves derived from the pelvic plexus, course along the posterolateral prostate at roughly the 5 and 7 o'clock positions before reaching the corpora cavernosa.
Why the bundles are the whole story
The single most consequential anatomical fact for sexual health is that the erectile nerves are not inside the prostate but plastered onto its outer surface in a thin, variable, often microscopic fascial plane. There is no clean dissection line. Walsh's anatomical work in the early 1980s mapped these bundles and made nerve-sparing prostatectomy conceivable, but even in expert hands the bundles can be stretched, cauterized, or devascularized. This is why a perfectly cured cancer can still leave a man with permanent erectile dysfunction, and why surgical volume and technique matter so much.
What people get wrong
Often saidThe prostate produces sperm
ActuallyNo, the testes produce sperm. The prostate contributes fluid (PSA, enzymes, zinc) that nourishes and liquefies semen; the seminal vesicles add the largest volume share.
Often saidRemoving the prostate just removes a gland
ActuallyIt also removes or injures the bladder-neck sphincter and risks the adjacent erectile nerves and the urinary sphincter, which is why incontinence and ED are the defining trade-offs.
Who profits, and who pushes back
Nobody is named here yet, because we have not done that work on this entry. Read that as unfinished. Somebody almost certainly sells this, and somebody almost certainly disputes it. Assume both until we have checked.
What we do not know
- How much of post-surgical ED is nerve injury versus vascular/cavernosal injury remains debated.
- Individual variation in bundle location limits how 'standardized' nerve-sparing can be.
At a glance
- Weight (young adult)
- ~20 g
- Seminal fluid share
- ~20-30% of ejaculate volume
- Zonal model
- McNeal, 1981
- Cancer origin
- Peripheral zone (~70%)
- BPH origin
- Transition zone
What this entry does not yet cover
What follows is unfinished work on our side, not a finding about Prostate Anatomy & Sexual Function. A short entry is not a safe entry.
- Timeline. We have not built the dated record of research and regulatory events.
- Cost and market. We have not documented what it sells for or who sells it.
- Supply chain. We have not mapped where it is made.
- Who uses it. We have not documented the user groups.
- What could change. No forward-looking summary yet.
- How it compares. We have not set it against the alternatives.
- Children and teenagers. We have not checked what is known about younger people.
- What can go wrong. We have not written the risk line for this one. Read the safety section below rather than treating its absence as reassurance.
- Where we land. We have not taken a position on this yet.
Sources
The studies below are named and described, but not linked. You cannot open them from here and check our reading against them, which means this page is our summary of the literature rather than a document you can verify. Weigh it accordingly until the links exist.
The studies that matter
McNeal, zonal anatomy of the prostate1981
Established the four-zone model still used for cancer and BPH localization
Walsh & Donker, cavernous nerve anatomy1982
Mapped the neurovascular bundles, enabling nerve-sparing radical prostatectomy
Lepor et al., periprostatic neuroanatomy1985
Detailed the posterolateral course of the cavernous nerves