In the example of childbirth the uterus contracts.  This pus…

In the example of childbirth the uterus contracts.  This pushes the baby’s head against the cervix.  Nerve endings in the cervix send a message to the brain that this is happening.  The brain secretes oxytocin.  Oxytocin stimulates the uterus to contract again and the baby’s head pushes even harder against the cervix.  Oxytocin is an example of: