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Information about Mastication

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Mastication or chewing is the process by which food is mashed and crushed 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 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) 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.

Muscles of mastication

Mastication is accomplished through the activity of the four muscles of mastication. Unlike most of the other facial muscles, which are innervated by the facial nerve, or CN VII, the muscles of mastication are all innervated by the trigeminal nerve, or CN V. More specifically, they are innervated by the mandibular branch, or V3. This is a testament to their shared embryological origin from the first branchial arch. The muscles of facial expression, on the other hand, derive from the second branchial arch.

In humans, the mandible, or lower jaw, is connected to the temporal bone of the skull via the temporomandibular joint, an extremely complex joint which permits movement in all planes. The muscles of mastication originate on the skull and insert into the mandible, thereby allowing for jaw movements during contraction. The mandible is the only bone that moves during mastication and other activities, such as talking.

Each of these primary muscles of mastication is paired, with each side of the mandible possessing one of the four. While these four muscles are the primary participants in mastication, other muscles are usually if not always helping the process, such as those of the tongue and the cheeks.

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 [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 analagous 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 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 firelines in advance of a wildfire.[1]

Notes

  1. http://jn.physiology.org/cgi/content/full/92/2/773 - Influence of age on adaptability of human mastication.

External links

Chewing tobacco is a smokeless tobacco product. Chewing is one of the oldest ways of consuming tobacco leaves. Native Americans in both North and South America chewed the leaves of the plant, frequently mixed with lime.
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Teeth (singular, tooth) are structures found in the jaws (or mouths) of many vertebrates that are used to tear, scrape, and chew food. Some animals, particularly carnivores, also use teeth for hunting or defense. The roots of teeth are covered by gums.
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Digestion is the process of metabolism whereby a biological entity processes a substance in order to chemically and mechanically convert the substance for the body to use.

Overview

Digestion occurs at the multicellular, cellular, and sub-cellular levels, usually in animals.
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Enzymes are proteins that catalyze (i.e. accelerate) chemical reactions.[1] In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, the products.
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Cheeks (Latin: bucca, also malā: "jaw") constitute the area of the face below the eyes and between the nose and the left or right ear.

It is fleshy in humans and other mammals, the skin being suspended by the chin and the jaws, and forming the lateral
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The tongue is the large bundle of skeletal muscles on the floor of the mouth that manipulates food for chewing and swallowing (deglutition). It is the primary organ of taste. Much of the surface of the tongue is covered in taste buds.
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In digestion, a bolus (from Latin bolus, ball) is a round mass of organic matter moving through the digestive tract. A bolus is initially shaped through chewing and swallowing of food and maintained as peristalsis moves it through the intestines, eventually being released as feces.
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Ruminantia

Families

Antilocapridae
Bovidae
Cervidae
Giraffidae
Moschidae
Tragulidae

A ruminant is any animal that digests its food in two steps, first by eating the raw material and regurgitating a semi-digested form known as cud,
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Cud is a portion of food that returns from a ruminant's stomach in the mouth to be chewed for the second time. More accurately, it is a bolus of semi-degraded food regurgitated from the reticulorumen of a ruminant.
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In human anatomy, the masseter is one of the muscles of mastication.

It is particularly powerful in herbivores to assist when they are chewing plants.

Origin and insertion of the two heads


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The temporalis muscle is one of the muscles of mastication.

Structure

It arises from the temporal fossa and the deep part of temporal fascia. It passes medial to the zygomatic arch and inserts onto the coronoid process of the mandible.
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The medial pterygoid (or internal pterygoid muscle), is a thick, quadrilateral muscle of mastication.

The mandibular branch of the fifth cranial nerve, the trigeminal nerve, innervates the medial pterygoid muscle.
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The lateral pterygoid (or external pterygoid) is a muscle of mastication with two heads.

Origin and insertion

The upper/superior head originates on the infratemporal surface and infratemporal crest of the greater wing of the sphenoid bone, and the lower/inferior
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The facial nerve is the seventh (VII) of twelve paired cranial nerves. It emerges from the brainstem between the pons and the medulla, and controls the muscles of facial expression, and taste to the anterior two-thirds of the tongue.
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The facial nerve is the seventh (VII) of twelve paired cranial nerves. It emerges from the brainstem between the pons and the medulla, and controls the muscles of facial expression, and taste to the anterior two-thirds of the tongue.
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The trigeminal nerve (the fifth cranial nerve, also called the fifth nerve or simply V) is responsible for sensation in the face. It is similar to the spinal nerves C2–S5, which are responsible for sensation in the rest of the body.
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The trigeminal nerve (the fifth cranial nerve, also called the fifth nerve or simply V) is responsible for sensation in the face. It is similar to the spinal nerves C2–S5, which are responsible for sensation in the rest of the body.
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The mandibular nerve (V3) is the largest of the three branches of the trigeminal nerve.

Structure

Roots

It is made up of two roots:
  • a large sensory root proceeding from the inferior angle of the trigeminal ganglion.

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The mandibular nerve (V3) is the largest of the three branches of the trigeminal nerve.

Structure

Roots

It is made up of two roots:
  • a large sensory root proceeding from the inferior angle of the trigeminal ganglion.

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In the development of vertebrate animals, the pharyngeal arches (also called branchial arches or gill arches in fish) develop during the fourth and fifth week in utero
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The facial muscles are a group of striated muscles innervated by the facial nerve that, among other things, control facial expression. These muscles are also called mimetic muscles.
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mandible (from Latin mandibūla, "jawbone") or inferior maxillary bone is, together with the maxilla, the largest and strongest bone of the face . It forms the lower jaw and holds the lower teeth in place.
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The temporal bones are situated at the sides and base of the skull.

The temporal bone supports that part of the face known as the temple.

Parts

Each consists of five parts:
  • Squama temporalis
  • Mastoid portion
  • Petrous portion
  • Tympanic part

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Temporomandibular joint is the jaw joint and is frequently referred to as TMJ. There are two TMJs, one on either side, working in unison. The name is derived from the two bones which form the joint: the upper temporal bone
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Proprioception (PRO-pree-o-SEP-shun (IPA pronunciation: [ˈpɹopɹiːoˌsɛpʃən]); from Latin proprius
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A para-functional habit or parafunctional habit is the habitual exercise of a body part in a way that is other than the most common use of that body part. The term is most commonly used by dentists, orthodontists, or maxillofacial specialists to refer to parafunctional uses
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A para-functional habit or parafunctional habit is the habitual exercise of a body part in a way that is other than the most common use of that body part. The term is most commonly used by dentists, orthodontists, or maxillofacial specialists to refer to parafunctional uses
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Mammalia
Linnaeus, 1758

Subclasses & Infraclasses
  • Subclass †Allotheria*
  • Subclass Prototheria
  • Subclass Theria

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