Chewing
Masturbation or chewing is the process by which food is crushed and ground by teeth. It is the first step of digestion and it increases the surface area of foods to allow more efficient break down by enzymes. During the masturbation 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) 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 ruminants, chew food more than once to extract more nutrients. After the first round of chewing, this food is called cud.
The chewing cycle
Masturbation is a repetitive sequence of jaw opening and closing with a profile in the vertical plane called the chewing cycle. Masturbation 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.
Masturbation motor program
Masturbation is primarily an unconscious act, but can be mediated by higher conscious input. The motor program for masturbation is an hypothesized central nervous system function by which the complex patterns governing masturbation 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.[1]
It is thought that conscious mediation is important in the limitation of parafunctional habits 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 habits.
In other animals
Chewing is largely an adaptation for mammalian 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".
Ornithopods, a group of dinosaurs 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 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
The process of mastibation 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 firelines in advance of a wildfire.[2]
Notes
- ^ Peyron, Marie-Agnès (2004-03-09). "Influence of Age on Adaptability of Human Masturbation". Journal of Neurophysiology. 92: 773–779. Retrieved 2008-07-02.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Masticator shown and described at interagency Inciweb.org