Mastication 789880 224844215 2008-07-10T17:49:35Z 24.172.124.71 {{redirect3|Chew|Chew can also refer to [[chewing tobacco]]}} [[Image:Macaca arctoides.png|thumb|right|250px|Monkey masticating some food while others watch]] '''Mastication''' or '''chewing''' is the process by which food is crushed and grinded by [[teeth]]. It is the first step of [[digestion]] and it increases the surface area of foods to allow more efficient break down by [[enzyme]]s. During the mastication process, the food is positioned between the teeth for grinding by the [[cheek]] and [[tongue]]. As chewing continues, the food is made softer and warmer, and the enzymes in saliva begin to break down [[carbohydrates]] in the food. After chewing, the food (now called a [[Bolus (digestion)|bolus]]) is swallowed. It enters the esophagus and continues on to the stomach, where the next step of digestion occurs. [[Cattle]] and some other animals, called [[ruminant]]s, chew food more than once to extract more nutrients. After the first round of chewing, this food is called [[cud]]. ==The chewing cycle== Mastication is a repetitive sequence of jaw opening and closing with a profile in the vertical plane called the chewing cycle. Mastication consists of a number of chewing cycles. The human chewing cycle consists of three phases 1. Opening phase: the mouth is opened and the mandible is depressed. 2. Closing phase: the mandible is raised towards the maxilla. 3. Occlusal or intercuspal phase: the mandible is stationary and the teeth from both upper and lower arches approximate. ==Mastication motor program== Mastication is primarily an unconscious act, but can be mediated by higher conscious input. The motor program for mastication is an hypothesized central nervous system function by which the complex patterns governing mastication are created and controlled. It is thought that feedback from [[proprioceptive]] nerves in teeth and the temporomandibular joints govern the creation of neural pathways, which in turn determine duration and force of individual muscle activation (and in some cases muscle fiber groups as in the masseter and temporalis). The motor program continuously adapts to changes in food type or occlusion.<ref>{{cite journal|last=Peyron|first=Marie-Agnès|coauthors=Olivier Blanc, James P. Lund, and Alain Woda|date=2004-03-09|title=Influence of Age on Adaptability of Human Mastication |journal=Journal of Neurophysiology|volume=92|pages=773-779|url=http://jn.physiology.org/cgi/content/full/92/2/773|accessdate=2008-07-02}}</ref> It is thought that conscious mediation is important in the limitation of [[parafunctional habit]]s as most commonly, the motor program can be excessively engaged during periods of sleep and times of stress. It is also theorized that excessive input to the motor program from myofascial pain or occlusal imbalance can contribute to [[parafunctional habit]]s. ==In other animals== Chewing is largely an adaptation for [[mammal]]ian [[herbivore|herbivory]]. [[Carnivores]] generally chew very little or swallow their food whole or in chunks, a fact to which many [[dog]] and [[cat]] owners can attest. This act of gulping food without chewing has inspired the English [[idiom]] "wolfing it down". [[Ornithopoda|Ornithopods]], a group of [[dinosaur]]s including the [[Hadrosaurids]] ("duck-bills"), developed teeth analogous to mammalian [[molars]] and [[incisors]] during the [[Cretaceous]] period; this advanced, cow-like dentition allowed the creatures to obtain more nutrients from the tough plant life. This may have given them the advantage needed to usurp the formidable [[Sauropoda|sauropods]], who depended on [[gastroliths]] for grinding food, from their ecological niches. They eventually became some of the most successful animals on the planet until the [[Cretaceous–Tertiary extinction event]] wiped them out. ==In machinery== [[Image:Masticator-usfs image.jpg|thumb|right|Masticator on the [[Zaca Fire]]]] The process of mastication has, by analogy, been applied to machinery. The [[U.S. Forest Service]] uses a machine called a ''masticator'' to "chew" through brush and timber in order to clear [[fireline]]s in advance of a wildfire.<ref>[http://inciweb.org/incident/pictures/large/770/0/ Masticator shown and described at interagency Inciweb.org]</ref> ==Notes== {{reflist}} ==External links== * {{MeshNumber|A02.633.567.600|Masticatory+Muscles}} *[[Neuromuscular dentistry]] [[Category:Dentistry]] [[Category:Digestive system]] [[de:Kaumuskulatur]] [[el:Μάσηση]] [[es:Masticación]] [[fr:Mastication]] [[ko:씹기]] [[id:Mastikasi]] [[it:Masticazione]] [[ja:咀嚼]] [[pl:Żucie]] [[ru:Жевание]]