Sensitivity: where it feels the most

One nerve, a crowd of free nerve endings and a small spot on the underside that men rank above everything else. Plus what arousal, age, your grip and your saddle do to it

Ask a man where his cock is most sensitive and he will point, without hesitating, just under the head. Anatomists took longer to get there but ended up in the same place. The surprise is what kind of sensitive it is: the glans is not a fingertip, and it was never meant to read Braille.

Here are the wiring, the hot spots, the territory around them that gay men know better than any textbook, and what arousal, age, your grip and your saddle do to it.

The wiring

Almost all the feeling in the penis travels along one nerve, the pudendal. It leaves the spinal cord low down, at the S2 to S4 level, and on its way forward it splits into three: the inferior rectal nerve for the skin around the anus, the perineal nerve for the perineum and the back of the scrotum, and finally the dorsal nerve of the penis.

The dorsal nerve runs along the top of the shaft. Dissections show two teams inside it: fibres for the glans that stay on top all the way and then branch richly inside the head, and fibres for the shaft that arc round towards the sides and the underside.

The frenulum gets a backup line. When volunteers had both dorsal nerves numbed, the top, the sides and the glans went numb, but the underside, frenulum included, still felt a pinprick: a branch of the perineal nerve reaches it too. The one spot men rate highest is also the one spot wired twice.

What is under the skin

Under the microscope, the glans is mostly free nerve endings, bare nerve tips in almost every fold of the skin, outnumbering corpuscular receptors about ten to one. Its corpuscles are genital end bulbs, also called Krause end bulbs: tangled balls of free endings, densest in the corona and near the frenulum.

What the glans lacks matters as much. Merkel endings and typical Meissner corpuscles, the receptors that let your fingertips read fine texture, are absent. So the glans is poor at fine detail but answers strongly to pressure, rubbing and pain. The anatomists called its sensibility "protopathic": crude and powerful rather than precise.

Meissner corpuscles do turn up on the foreskin, in a ridged band of mucosa near its tip. Whether losing them changes how sex feels is a debate with its own page: Cut or uncut: does it change sensitivity?

The hot spots, by men themselves

In 2009 Schober and colleagues gave 81 healthy men aged 22 to 57 a questionnaire with drawings and asked them to rate each area for pleasure, orgasm intensity and the effort needed to come. The ranking for pleasure, penis only:

Underside beats top, head beats shaft, and the two meet at the frenulum, where most men point. Not every step of the ranking was statistically solid, only 11 of the men were uncut, and the sample was small, but it matches the anatomy above. For how the frenulum is built, and what happens when it is too short, see Foreskin.

Same nerve, further back

The same study ranked, after the penis, the skin between the scrotum and the anus, the back and front of the scrotum, and the area around the anus. Among other body parts that helped them come, the men listed the scrotum, ears, perineum, neck, nipples, buttocks, the skin of the anus and the anus with penetration.

None of this surprises a gay man, and the wiring explains it: perineum, scrotum and anus sit on branches of the same pudendal nerve as the cock. Same circuit, another door. The men in the study were not chosen for being gay, and we found no mapping study of gay men.

Arousal, age and the death grip

Arousal. After an erotic video, 30 men detected faint vibrations on a fingertip better than before. The cock is less straightforward: when an erection was produced with an injection, without arousal, the penis needed a stronger vibration to notice it. Detecting a buzz and enjoying a touch are different jobs.

Age. Pooling 13 studies, the vibration threshold of the penis rises with age, slowly at first and faster later, and higher still in men with erection problems. Worth knowing before blaming a partner's technique.

The death grip. The internet's favourite theory: years of wanking with a tight fist, or face down on the mattress, train the cock to need more than a mouth or an arse can give. There is something to it, but less than the forums suggest. Sex therapists see an "idiosyncratic" style, one no partner can reproduce, in many men who struggle to come with a partner. A 1998 paper described four men who masturbated face down daily for years and had erection or orgasm problems. A Chinese study of 24 men with lifelong delayed ejaculation found more frequent and more unusual masturbation, and higher touch thresholds on the shaft but not the glans. Clinic observations and small comparisons: nobody has measured whether grip strength causes anything. The usual advice, a looser grip, more lube, some variety, is harmless but untested.

Numb after cycling

Here the evidence is firmer. A narrow saddle presses on the perineum, right where the pudendal nerve and its arteries run. After a 540 km Norwegian touring race, 33 of 160 male riders had a numb or less sensitive penis, ten of them for more than a week, and 21 reported erection problems.

The fix is mostly mechanical. When 90 American bicycle police officers rode a noseless saddle for six months, pressure on the perineum fell by 66%, men free of genital numbness rose from 27% to 82%, and penile sensitivity improved. In a survey of 3,932 men, cyclists had no worse erections than swimmers and runners, and standing on the pedals over a fifth of the time, or a handlebar level with the saddle or higher, went with less numbness.

Sensitivity is only the input. For what the body does with it, see Erection and Ejaculation.