Answer:
Milk removal from the breast is accomplished by the contraction of myoepithelial cells, whose processes form a basket-like network around the alveoli where milk is stored , in concert with sucking by the infant.
When the infant is suckled, afferent impulses from sensory stimulation of nerve terminals in the areolus travel to the central nervous system where they promote the release of oxytocin from the posterior pituitary.
In the woman oxytocin release is often associated with such stimuli as the sight or sound or even the thought of the infant indicating a large cerebral component in this "neuroendocrine reflex".
The oxytocin is carried through the blood stream to the mammary gland where it interacts with specific receptors on myoepithelial cells, initiating their contraction and expelling milk from the alveoli into the ducts and sub-areolar sinuses.
The passage of milk through the ducts is facilitated by longitudinally arranged myoepithelial cell processes whose contraction shortens and widens the ducts, allowing free flow of milk to the nipple. The process by which milk is forceably moved out of the alveoli is called milk ejection or let-down and is essential to milk removal from the lactating breast.