Final answer:
The myometrium is a thick layer of smooth muscle cells in the middle of the uterus that allows for uterine contractions during labor and the expulsion of menstrual blood.
Step-by-step explanation:
The myometrium is the middle layer of the uterus, consisting of a thick layer of smooth muscle cells. These muscle fibers run horizontally, vertically, and diagonally, allowing the powerful contractions during labor and the contractions that expel menstrual blood. Anteriorly directed myometrial contractions occur near ovulation, possibly facilitating sperm transport.