Chewing

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(Redirected from
Mastication
)
"Chew" redirects here. For other uses, see Chew (disambiguation).
A stump-tailed macaque using mastication to process tough plant matter

Chewing or mastication is the process by which

teeth. It is the first step in the process of digestion, allowing a greater surface area for digestive enzymes
to break down the foods.

During the mastication process, the food is positioned by the

carbohydrates in the food. After chewing, the food (now called a bolus) is swallowed. It enters the esophagus and via peristalsis continues on to the stomach, where the next step of digestion occurs.[1] Increasing the number of chews per bite increases relevant gut hormones.[2] Studies suggest that chewing may decrease self-reported hunger and food intake.[2] Chewing gum has been around for many centuries; there is evidence that northern Europeans chewed birch bark tar
9,000 years ago.

Chewing, needing specialized teeth, is mostly a mammalian adaptation that appeared in early

Synapsids
, though some later herbivorous dinosaurs, since extinct, had developed chewing too. Nowadays, only mammals chew in the strict sense of the word, though some fishes have a somewhat similar behavior. Neither birds, nor amphibians or any living reptiles chew.

Premastication is sometimes performed by human parents for infants who are unable to do so for themselves. The food is masticated in the mouth of the parent into a bolus and then transferred to the infant for consumption[3] (some other animals also premasticate).

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.

A piece of chewing gum after being trodden on.

Chewing motor program

A water buffalo chewing cud

Chewing is primarily an unconscious (semi-autonomic) act, but can be mediated by higher conscious input. The motor program for mastication is a 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).

This motor program continuously adapts to changes in food type or occlusion.[4] This adaptation is a learned skill that may sometimes require relearning to adapt to loss of teeth or to dental appliances such as dentures.

It is thought that conscious mediation is important in the limitation of

parafunctional habits
.

Muscles

Main article: Muscles of mastication

Nutrition and health

Chewing stimulates

systemic review found evidence that chewing can decrease self-reported hunger and therefore food intake.[7] Eating food which does not require chewing, by choice or due to medical reasons as tooth loss, is known as a soft diet. Such a diet may lead to inadequate nutrition due to a reduction in fruit and vegetable intake.[8]

Chewing also stimulates the hippocampus and is necessary to maintain its normal function.[9] Chewing stimulates hippocampal neurogenesis in both humans and mice.[10]

In other animals

Chewing is largely an adaptation for

herbivory. Carnivores generally chew very little or swallow their food whole or in chunks.[11] This act of gulping food (or medicine pills) without chewing has inspired the English idiom
"wolfing it down".

Other animals such as cows chew their food for long periods to allow for proper digestion in a process known as rumination. Rumination in cows has been shown by researchers to intensify during the night. They concluded that cows chewed more intently in the night time compared to the morning.[12]

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 compete with the formidable sauropods, who depended on their massive gastrointestinal tracts to digest food without grinding it,[13] in their ecological niches. They eventually became some of the most successful animals on the planet until the Cretaceous–Paleogene extinction event
wiped them out.

In machinery

Masticator on the Zaca Fire

The process of chewing has, by analogy, been applied to machinery. The

firelines in advance of a wildfire.[14]

A cold press juicer uses the mastication process to extract juice from fruit and vegetable without the loss of oxygen or heat-sensitive nutrients as there is less friction involved.[15]

See also

Notes

  1. ^ "Prehension, Mastication and Swallowing". Archived from the original on 2015-07-15. Retrieved 2012-05-24.
  2. ^
    PMID 26188140
    .
  3. PMID 17704036
  4. PMID 15277595
    . Retrieved 2008-07-02.
  5. PMID 21738616
    .
  6. PMID 19144727
    .
  7. S2CID 15350810
    .
  8. PMID 12131890
    .
  9. PMID 26078711
    .
  10. ^ Smith, Natalie, Miquel-Kergoat, Sophie, and Thuret, Sandrine. 'The Impact of Mastication on Cognition: Evidence for Intervention and the Role of Adult Hippocampal Neurogenesis'. 1 Jan. 2015 : 115 – 123.
  11. doi:10.4159/harvard.9780674184404.c14
    .
  12. PMID 17369233
    .
  13. S2CID 206514245
    .
  14. ^ Masticator shown and described at interagency Inciweb.org[permanent dead link]
  15. ^ Madison (15 May 2019). "10 Best Cold Press Juicer (Slow Juicer) 2020 - Reviews & Buying Guide". Cookware Stuffs. Retrieved 2020-03-20.

External links

Wikimedia Commons has media related to Mastication.
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