LANGENBACH, G.E.J.: Mammalian feeding

In mammals, basic symmetrical food transport cycles have been described for lapping and soft food ingestion. To increase chewing efficiency a unilateral occlusal motion has been evolved replacing the slow closing phase in the basic cycle. This power stroke is preceded by fast opening and closing phases increasing the gape. Jaw opening is produced by action of the digastrics and hyoidal muscles, often supported by activity of the lateral pterygoid muscles. Activity of these muscles is usually asymmetric, moving the jaw to the working side. The relative uniformity of the mammalian jaw closer motor patterns is striking. Nevertheless, several specialisms, clearly different from the primitive mammalian asymmetric masticatory motor pattern, can be distinguished. Weijs (1994) proposed to categorise these into four groups, the carnivore symmetric, the rodent symmetric, the transverse and the alternate patterns. In contrast to the relative uniformity in motor patterns, the anatomical diversity of jaw systems is impressive and probably reflects the adaptation to diet. Mostly in the last decade, this diet influence has been investigated. With tougher foods, an increase in the closing activity has been found, in combination with a prolonged duration and often extended transverse dimension of the power stroke. Data suggest that the individual masticatory cycles are largely shaped by sensory feedback. Also the suckling food intake preceding mastication has been a point of interest. It seems that mammals use expression and suction mechanisms to collect the milk. Both motor patterns resemble that of mastication, suggesting that transition could be gradual. Recently, dynamic computer 3D-modeling has emerged as an analytical tool. The approach has the potential to help explain how structure and function interact, and to elucidate the existence of different feeding motor patterns.