MASTICATION

"Chew" redirects here. "Chew" is also a nickname for chewing tobacco. For the Marvel comics superhero, see Dane Chew.

Mastication or chewing is the process by which food is torn and/or 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. 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.

Mastication is chiefly possible thanks to powerful muscles, masseter and temporalis, as well as smaller muscles that allow fine control. They move the mandible against the upper jaw and enable crushing of relatively hard food.

In humans, the mandible is connected with the temporomandibular joint that permits forward-backward and side to side movement.

Some animals, called ruminants, chew food more than once. These animals, such as cows, chew their food more than once for the extra nutrients in it. This food is called cud.

Muscles of mastication

Chewing food is a complex motor function, muscles need to be powerful enough to break tough portions of food, yet have enough dexterity to not injure the tongue, and to clear the mouth completely.

The primary muscles of mastication, each of which is paired, are the temporalis, masseter, medial pterygoid and lateral pterygoid. These muscles attach to the mandible at various points in order to move the mandible in all directions.

All the muscles of mastication are supplied by the mandibular nerve (V₃), which is a branch of the trigeminal nerve that mostly carries sensation from the face.

All muscles involved in human mastication

Important muscles in bold.

• Anterior belly of digastric
• Buccinator muscle
• Depressor anguli oris muscle
• Depressor labii inferioris muscle
• Lateral pterygoid muscle
• Levator anguli oris muscle
• Levator labii superioris alaeque nasi muscle
• Levator labii superioris muscle
• Levator veli palatini muscle
• Masseter muscle
• Medial pterygoid muscle
• Mentalis muscle
• Orbicularis oris muscle
• Superior pharyngeal constrictor muscle
• Temporalis muscle
• Tensor veli palatini muscle
• Tongue
• Zygomaticus major muscle
• Zygomaticus minor muscle

Mastication motor program

Mastication is primarily an unconscious act, but can be mediated by higher conscious input. The motor program for mastication is an hypothesised 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 fibre 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.

Notes

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

External links

• MeSH A02.633.567.600
• Neuromuscular dentistry

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