Relationship between Corpus Spongiosum Pressure and Glans erection
We’ve talked a lot about the effect of the contraction of the Ischiocavernosus muscles on the pressure within the cavernosa (Girth theory: Pumping vs. clamping). These contractions are the result of reflex activation at full erection. These contractions drive the internal cavernosa pressures much higher than the upper blood pressure number (systolic blood pressure).
The same appears to be true in the spongiosum. The bulbocavernosus muscles wrap around the bulb of the penis which is the base of the spongiosum. The reflex contractions of the BC muscles drive the spongiosum pressures above systolic pressure. This appears to be very important to the phases of engorgement of the glans.
A study in rats looked at spongiosum pressure, BC muscle contraction and gland erection. They described 3 phases of glans erection: E1, weak glans engorgement; E2, involving some dilation of the distal glans; and E3, intense flaring of the glans. The intensity of glans erection was directly related to spongiosum pressure. This pressure was directly related to the intensity and duration of bursts of the contractions of the BC muscles.
The pressures in the spongiosum of the rat that result from BC muscle contraction were very high. The pressures in the spongiosum corresponding to the glans erection phases were 225 mm Hg (E1), 375 mm Hg (E2) and 550 mm Hg (E3). These pressure peaks were short, in milliseconds (1000 milliseconds = 1 second). The contraction bursts seen in rats with E1 glans erections had short contraction bursts of about 300 millisecond durations, but at E3 the BC muscle contraction durations were over 800 milliseconds. In addition, the frequency at which these BC contraction bursts occur also increased with the phases of glans erection.
They concluded:
Quote
"Our results provide further evidence that penile erections involve both vascular-subsystolic [filling of the low pressure erection chambers of the penis by the arteries] and muscular-suprasystolic [pressures elevation above arterial pressure in the erectile chambers by muscle contraction] phases."Schmidt MH, et al. Corpus spongiosum penis pressure and perineal muscle activity during reflexive erections in the rat. American Journal of Physiology 269 (Regulatory Integrative and Comparative Physiology 38) (1995) R904 - R913.
The rat penis is much different than the human penis. Copulation in the rat is short and thrusts are rapid. The head and the shaft must be bone hard. Does this have any relationship to us. I think so. We know from personal experience that Kegels increase the size of my penis head with each contraction when approaching full erection. We also know that at peak erection our head mushrooms to a very firm structure. The pressure in the head is much higher than arterial pressure. BC muscle contraction must be involved.
I have yet to find a study that have measured spongiosum pressure in humans. We all believe that the pressures must be low enough to allow for ejaculation. But they must be high enough so the the glans can reach maximal erection. How the single layer tunica covering the spongiosum is involved needs to be further developed by us.