x.3.2.2.6 Muscles
The vagina is a tract of autonomically innervated smooth muscles (a longitudinal inner layer and a circular outer layer) surrounded by three strong striated pelvic floor muscles: the mm. ischiocavernosus, and bulbocavernosus and m. perinea at the surface, and internally the m. levator ani. These three muscles together form the pelvic diaphragm that closes off the anterior part of the lesser pelvis. The largest median part of the diaphragm is known as the musculus pubococcygeus. Until now it has not been possible to monitor – simultaneously but separately – the activity of the smooth and striated muscles during sexual arousal.
The smooth muscles of the uterus and vagina are also continually active in non-erotic conditions. This activity increases around menstruation in order to evacuate the contents of the uterus and vagina. These contractions are sometimes painful. This is known as dysmenorrhoea. The pressure in the vagina increases during sexual arousal. At the moment of orgasm, this culminates in a series of clonic contractions of the striated pelvic floor muscles at intervals of 0.8 seconds. This interval gradually becomes longer and the contractions weaker. This can take 5 to 60 seconds. These contractions are accompanied by the orgasm sensation. Random contractions of the striated muscles do not bring about a feeling of intense pleasure, although they do intensify arousal. Uterus contractions can also occur during sexual arousal, and a whole series may occur during orgasm. Uterus contractions can contribute to the feeling of orgasm, but are not essential for this for all women.