Final answer:
The myometrium, a thick layer of smooth muscle tissue, is the uterine layer highly responsive to oxytocin, facilitating contractions for childbirth.
Step-by-step explanation:
The uterine layer that is most responsive to the hormone oxytocin, which increases contractions and leads to the expulsion of the fetus, is the myometrium. This layer is a thick layer of smooth muscle tissue and is responsible for the powerful contractions during labor. These muscle fibers running in multiple directions facilitate the strong contractions needed for childbirth, as well as less powerful contractions for expelling menstrual blood.