Nipple: The nipple is a elevated structure situated in the center with the breast. It includes small muscles that contract in response to stimulation. When the breasts are stimulated via the suckling of her newborn, the mother's brain secretes oxytocin. Superior levels of oxytocin induce the contraction of muscle mass https://grok.com/share/c2hhcmQtMw%3D%3D_5ad6450c-533d-442c-a09c-9f7bce1babfb