When a baby begins to suckle at the breast, sensory receptors in the nipple send signals to the brain, prompting the release of oxytocin. This hormone then triggers the contraction of myoepithelial cells surrounding the alveoli, pushing milk into the milk ducts and towards the nipple. This allows the milk to flow more easily into the baby's mouth. It's worth noting that the let down reflex can also be triggered by emotional stimuli such as hearing a baby cry or thinking about the baby.
