The cervix is the lower portion of the uterus or womb. More specifically, it is the narrow passage that connects the uterus to the vagina. It is the only part of the uterus that is visible, and therefore accessible, to a doctor for sampling tissue as in the case of pap smears.
A tiny opening in the uterus, called the os, remains open when a woman is not pregnant, allowing menstrual blood to flow out of the uterus and sperm to enter it. When a woman becomes pregnant, the os closes tightly to protect the fetus. When a woman is ready to give birth, the os opens again and the cervix begins to widen, or dilate, to allow the fetus to pass out of the uterus and into the birth canal.
More About Cervix
While it's not possible for a man to penetrate the cervix during sex, some well-endowed men may bump into it on occasion. This can be uncomfortable or even painful for a woman. To help prevent this, a couple can use shallow-penetration sex positions, such as the spoon position. Woman-on-top positions are also a good option because they allow a woman to control the depth and speed of thrusts during intercourse. A woman should also be fully aroused before intercourse, since her vaginal canal actually lengthens during sexual arousal in anticipation of penetration.
