What Is The Cervix?

The cervix (or neck of the uterus) is the lower, narrow portion of the uterus where it joins with the top end of the vagina. It is cylindrical or conical in shape and protrudes through the upper anterior vaginal wall. 

Approximately half its length is visible with appropriate medical equipment; the remainder lies above the vagina beyond view. It is occasionally called "cervix uteri". 

During menstruation the cervix stretches open slightly to allow the endometrium to be shed. This stretching is believed to be part of the cramping pain that many women experience. Evidence for this is given by the fact that some women's cramps subside or disappear after their first vaginal birth because the cervical opening has widened. During childbirth, contractions of the uterus will dilate the cervix up to 10 cm in diameter to allow the child to pass through.

Stimulation of the cervix leads to orgasm for some women. During orgasm, the cervix convulses and the external os dilates. Dr. R. Robin Baker and Dr. Mark A. Bellis, both at the University of Manchester, first proposed that this behavior would tend to draw semen in the vagina into the uterus, increasing the likelihood of conception.

Changes in the Cervix

The below picture shows a cervix that is dilating. The top left shows a cervix that is not dilated or effaced. The top right show early effacement (thinning out). See how the effacement is making the cervix shorter. The bottom left show the cervix completely effacted, but not fully dilated. The bottom right shows the cervix to be completely dilated and effaced. As you can see the cervix must thin out before it can "shrink up" and begin to dilate. 

During childbirth, the cervix is opened (dilated) and thinned out (effaced) by the contractions of the uterus. When you have a contraction, the cervix pulls up. This action is sort of like trying to put on a turtle neck sweater. Imagine putting your head through a turtle neck without gathering up the long neck. You will have a hard time putting it on. Now imagine putting on a turtle neck after gathering the neck up. This is much easier. This is what your cervix must do before opening up.