Rooting and sucking are primal reflexes in a baby. In fact, the fetus swallows amniotic fluid before birth. The instinctive process of swallowing is amazing. It begins when a force of fluid, mainly from movements of the tongue, is sensed at the back of the throat in the oropharynx. The nasopharynx, or the part of the pharynx connected to the nasal passages, closes off with the motion of the soft palate and tightening of the muscles of the pharynx. Breathing is momentarily suppressed, and tightening of the laryngeal muscles shuts off the glottis and raises the larynx at the same time.
With a breastfeeding mom, following a milk ejection (let-down reflex), a fully sufficient amount of milk is available in the the area just under the areola, which drains out through the nipple. Each suck is followed by a swallow. This pattern repeats quickly and continuously as long as milk is immediately available and the baby is hungry -- about 1 suck per second. We call this "nutritive sucking." There is high milk flow during this period of frequent swallowing.
Many moms refer to "non-nutritive sucking" as "using me as a pacifier." This kind of sucking is the sequence that occurs when fluid is not introduced into the baby's mouth. Non-nutritive sucking may occur in a few different instances:
- When the baby is at the breast and the lactiferous sinuses aren't full
- Between nutritive sucks
- At the end of a feeding
Another important variable that comes into play here is flow rate, or how quickly milk comes out, which affects how quickly the baby will suck and swallow. The faster the milk flows, the faster the baby will suck and swallow. In bottle feeding, flow rates are generally very consistent; in breastfeeding, they are extremely inconsistent. Before and between milk ejections, and at the end of feedings, the flow rate is very low. However, during the first and subsequent milk ejections, the flow rates are very high. So, different than on the bottle, babies who are breastfeeding will typically have both nutritive and non-nutritive sucking.
Riordan J and Auerbach KG. Breastfeeding and Human Lactation. Jones and Bartlett. 108-115.