Final answer:
During natural childbirth, pain perception is reduced due to the release of endorphins, which are the body's natural painkillers. These are responsible for the euphoric feelings and pain reduction that Mary experienced during childbirth, rather than neurotransmitters like serotonin or norepinephrine.
Step-by-step explanation:
When Mary underwent natural childbirth and felt less pain, it is likely due to an increase in the neurotransmitter endorphins. Endorphins are the body's natural painkillers and are released in response to stress and pain. They are known to produce a feeling of euphoria, which can explain Mary's heightened happiness while giving birth.
Detailed studies on labor and birth have shown that the hormone oxytocin causes the contraction of the uterine wall muscles, promoting the expulsion of the fetus. This is a part of a positive feedback loop during childbirth, where increased contractions lead to more oxytocin release and so on, until the baby is delivered. After birth, when the stretching of the cervix stops, so does the additional oxytocin release.
The natural occurrence of pain reduction during childbirth is not primarily linked to neurotransmitters like serotonin or norepinephrine. Instead, it is the endorphins, coupled with the intensive hormonal activity involving oxytocin, that play a significant role in managing the pain and emotional response during childbirth.