ANATOMY AND PHYSIOLOGY OF THE MOUTH

1. ANATOMY AND PHYSIOLOGY OF THE MOUTH Richard H. Moore, Ph.D.

2. Learning Objectives After completing this module, the participant will be: Familiar with the basic anatomy of the mouth and associated structures Familiar with the normal functions of the teeth, tongue and salivary glands including mastication, swallowing and speech articulation Familiar with how the sense of taste normally functions

3. Supplemental Documents The Case Study, Glossary, References, Evaluation Form, and Pre-Post Test with answers for this module are found on a separate Word document.

4. Opening Activity Case Study �Do it Yourself�

5. The Mouth or Oral Cavity Common entrance to the digestive and respiratory tracts Site for entry of foodstuffs Initial processing of food called mastication Articulation of speech Alternate airway The Mouth or Oral Cavity is the common entrance to the digestive and respiratory tracts. It serves as the site of entry for foodstuffs into the body, for the initial processing or mastication of those foodstuffs and also, as a site for articulation in speech and as an alternate airway. The Mouth or Oral Cavity is the common entrance to the digestive and respiratory tracts. It serves as the site of entry for foodstuffs into the body, for the initial processing or mastication of those foodstuffs and also, as a site for articulation in speech and as an alternate airway.

6. Anatomy of the Mouth Delimited anteriorly by the lips and posteriorly by the anterior tonsillar pillars The roof of the mouth is formed by the hard and soft palates The floor of the mouth is formed by the tongue The walls are lined by the buccal mucosa Anatomically, the mouth is delimited anteriorly by the lips and posteriorly by the anterior tonsillar pillars. The roof of the mouth is formed by the hard and soft palates. The floor of the mouth by the tongue, a muscular structure that contains the organs of taste found in the taste buds and the mucosa, overlying the sublingual and submandibular salivary glands. The walls are lined by the buccal mucosa. Anatomically, the mouth is delimited anteriorly by the lips and posteriorly by the anterior tonsillar pillars. The roof of the mouth is formed by the hard and soft palates. The floor of the mouth by the tongue, a muscular structure that contains the organs of taste found in the taste buds and the mucosa, overlying the sublingual and submandibular salivary glands. The walls are lined by the buccal mucosa.

7. Division of the Mouth The mouth is divided into two cavities by the teeth. The vestibule is between teeth and cheeks. The outside surface of the teeth is the buccal surface. The oral cavity is internal to the teeth. The inside surface of the teeth is the lingual surface. The mouth is divided into two cavities by the teeth. The vestibule is between teeth and cheeks. The outside surface of the teeth is the buccal surface, while the oral cavity is internal to the teeth. The inside surface of the teeth is the lingual surface. � The mouth is divided into two cavities by the teeth. The vestibule is between teeth and cheeks. The outside surface of the teeth is the buccal surface, while the oral cavity is internal to the teeth. The inside surface of the teeth is the lingual surface. �

8. Anatomical Features of the Mouth Alveolar processes of the mandible and maxilla and teeth Tongue Salivary glands Alveolar processes of the mandible and maxilla and teeth. These are the ridges or bony faces of the mandible or maxilla that contain the tooth sockets. � The tongue, anterior to the circumvallate papilla, the posterior portion of the tongue, technically falls outside the limits of the mouth. The tongue is a muscular organ on the floor of the mouth that aids in mastication, swallowing and the articulation of sound, as well as being the site of the sense of taste. Major and minor salivary glands produce and secrete saliva. There are three pairs of major salivary glands, one of each pair on each side. In addition to the major salivary glands, there are minor salivary glands as well as numerous small accessory salivary glands scattered over the palate, lips, cheeks, tonsils and tongue. These lie in the tissues that surround the mouth, and technically, are not in the mouth proper. However, they are functionally tied into the mouth and must be considered part of the oral system. Alveolar processes of the mandible and maxilla and teeth. These are the ridges or bony faces of the mandible or maxilla that contain the tooth sockets. � The tongue, anterior to the circumvallate papilla, the posterior portion of the tongue, technically falls outside the limits of the mouth. The tongue is a muscular organ on the floor of the mouth that aids in mastication, swallowing and the articulation of sound, as well as being the site of the sense of taste. Major and minor salivary glands produce and secrete saliva. There are three pairs of major salivary glands, one of each pair on each side. In addition to the major salivary glands, there are minor salivary glands as well as numerous small accessory salivary glands scattered over the palate, lips, cheeks, tonsils and tongue. These lie in the tissues that surround the mouth, and technically, are not in the mouth proper. However, they are functionally tied into the mouth and must be considered part of the oral system.

9. Teeth and Alveolar Processes Calcified, enamel � hardest substance in body Embedded in bony sockets of alveolar processes Humans have two sets: Deciduous - �milk� or �baby� teeth Permanent Teeth are hard, calcified structures embedded in the bone of the jaws that perform the primary function of mastication. Humans like most other mammals initially have a temporary set of teeth, the decidual, called milk or baby teeth. In humans, tooth development begins in the fetus at about 6 weeks of age when the basic substance of the tooth forms. The milk teeth, numbering 20 in humans including: Two (2) central incisors, two (2) lateral incisors, two (2) canines and four (4) premolars in each jaw, usually appear at between six and 24 months. At about six years of age, permanent teeth begin to replace the deciduous teeth. The last of the permanent teeth or wisdom teeth may not appear until the 25th year and in some persons, not at all. The permanent teeth generally number 32 in all: Four (4) incisors, Two (2) canines, four (4) bicuspids and four (4) molars, six, if wisdom teeth develop, in each jaw. Although teeth are among the hardest and frequently, longest lasting parts of the body, they can exhibit considerable wear and tear associated with a lifetime of eating tough, fibrous foodstuffs. The extent of wear on the teeth has been used as a method of aging other mammals. The expression, �Never look a gift horse in the mouth.� comes about from the fact the age and overall condition of a horse can often be ascertained by examining their teeth. A horse may at first appear to be a valuable gift, but close scrutiny may reveal its true age and value. The same can be said for any gift. Teeth are hard, calcified structures embedded in the bone of the jaws that perform the primary function of mastication. Humans like most other mammals initially have a temporary set of teeth, the decidual, called milk or baby teeth. In humans, tooth development begins in the fetus at about 6 weeks of age when the basic substance of the tooth forms. The milk teeth, numbering 20 in humans including: Two (2) central incisors, two (2) lateral incisors, two (2) canines and four (4) premolars in each jaw, usually appear at between six and 24 months. At about six years of age, permanent teeth begin to replace the deciduous teeth. The last of the permanent teeth or wisdom teeth may not appear until the 25th year and in some persons, not at all. The permanent teeth generally number 32 in all: Four (4) incisors, Two (2) canines, four (4) bicuspids and four (4) molars, six, if wisdom teeth develop, in each jaw. Although teeth are among the hardest and frequently, longest lasting parts of the body, they can exhibit considerable wear and tear associated with a lifetime of eating tough, fibrous foodstuffs. The extent of wear on the teeth has been used as a method of aging other mammals. The expression, �Never look a gift horse in the mouth.� comes about from the fact the age and overall condition of a horse can often be ascertained by examining their teeth. A horse may at first appear to be a valuable gift, but close scrutiny may reveal its true age and value. The same can be said for any gift.

10. Deciduous vs. Permanent Teeth Deciduous Teeth: Erupt at 6 months to one year 20 in number (2/2,1/1,2/2) Permanent Teeth: Erupt between 6 and 18+ years 32-36 in number (2/2, 1/1, 2/2, 2-3/ 2-3)

11. Structure of a Tooth Enamel - the outer layer of the tooth. New enamel is only produced before the eruption of the tooth. Dentin - the inner layer and the main part of the tooth. Pulp - part of the inside of the tooth that contains the nerve. Root - the part of the tooth that secures the tooth into the jaw. The tooth consists of a crown, the portion visible in the mouth, and one or more roots that extend down in the tooth socket or alveolar process. The portion of the gum surrounding the root, known as the periodontal membrane, cushions the tooth in its bony socket. The maxillary and mandible bones of the jaws serve as sites for the firm anchorage of the root. The center of the crown is filled with soft, pulpy tissue containing blood vessels and nerves that represent extensions of the Trigeminal or V. cranial nerve. This tissue extends to the tip of the root by means of a canal. Surrounding the pulp and making up the greater bulk of the tooth is a hard, bony substance called dentin. The root portion has an outer layer of cementum, while the crown is coated by an additional layer of enamel, the hardest substance in the body. The tooth consists of a crown, the portion visible in the mouth, and one or more roots that extend down in the tooth socket or alveolar process. The portion of the gum surrounding the root, known as the periodontal membrane, cushions the tooth in its bony socket. The maxillary and mandible bones of the jaws serve as sites for the firm anchorage of the root. The center of the crown is filled with soft, pulpy tissue containing blood vessels and nerves that represent extensions of the Trigeminal or V. cranial nerve. This tissue extends to the tip of the root by means of a canal. Surrounding the pulp and making up the greater bulk of the tooth is a hard, bony substance called dentin. The root portion has an outer layer of cementum, while the crown is coated by an additional layer of enamel, the hardest substance in the body.

12. Physiology of Teeth Mineral and vitamin requirements for maintenance: Calcium Phosphorous Vitamin D Vitamin C Decay / Cavities or Caries Sufficient calcium, phosphorus and vitamins D and C are necessary for the development and maintenance of sound teeth. The most common disorder that affects the teeth is dental caries of tooth decay. A widely accepted explanation of the process of tooth decay is that salivary bacteria convert carbohydrate particles in the mouth into lactic acid, which attacks the enamel, dentin, exposed cementum and, if left untreated, the pulp of the teeth. Regular cleansing and dental examinations are important in preventing dental caries and gum disorders. Fluoridation of public water supplies and use of fluoride toothpastes also help prevent caries. Sufficient calcium, phosphorus and vitamins D and C are necessary for the development and maintenance of sound teeth. The most common disorder that affects the teeth is dental caries of tooth decay. A widely accepted explanation of the process of tooth decay is that salivary bacteria convert carbohydrate particles in the mouth into lactic acid, which attacks the enamel, dentin, exposed cementum and, if left untreated, the pulp of the teeth. Regular cleansing and dental examinations are important in preventing dental caries and gum disorders. Fluoridation of public water supplies and use of fluoride toothpastes also help prevent caries.

13. Tongue Muscular organ Functions in: Chewing Swallowing Speech Site of sensory reception: Taste Touch Pain / Temperature The Tongue: In humans, the tongue is a muscular organ which principally functions in chewing, swallowing and speaking. Sensitivity to all tastes is distributed across the whole tongue and indeed, to other regions of the mouth where there are taste buds. But, some areas are more responsive to certain tastes than others. The appearance of the tongue is often an indication of body health; a pinkish-red color is normal. � � The Tongue: In humans, the tongue is a muscular organ which principally functions in chewing, swallowing and speaking. Sensitivity to all tastes is distributed across the whole tongue and indeed, to other regions of the mouth where there are taste buds. But, some areas are more responsive to certain tastes than others. The appearance of the tongue is often an indication of body health; a pinkish-red color is normal. � �

14. Papillae1 Sites of Taste Buds Classified by shape: circumvallate foliate fungiform filiform - non-gustatory The tongue is covered by a mucous membrane containing small projections called papillae, which give it a rough surface. Taste papillae can be seen on the tongue as little red dots, or raised bumps, particularly at the front of the tongue. These ones are actually called fungiform papillae, because they look like little button mushrooms. There are three other kinds of papillae, foliate, circumvallate and the non-gustatory filiform, often misspelled filliform. Taste buds, on the other hand, are collections of cells on these papillae and cannot be seen by the naked eye.1The tongue is covered by a mucous membrane containing small projections called papillae, which give it a rough surface. Taste papillae can be seen on the tongue as little red dots, or raised bumps, particularly at the front of the tongue. These ones are actually called fungiform papillae, because they look like little button mushrooms. There are three other kinds of papillae, foliate, circumvallate and the non-gustatory filiform, often misspelled filliform. Taste buds, on the other hand, are collections of cells on these papillae and cannot be seen by the naked eye.1

15. Taste Buds1,2 Microscopic Contained in and on papillae Different types of cells perform different functions Also found elsewhere in mouth Tiny taste organs or taste buds are scattered over the entire surface of the papillae, with large numbers concentrated on the circumvallate papillae, toward the middle of the tongue. Other types of papillae include the filiform papillae that occur along the border of the tongue and the fungiform or mushroom-shared papillae that occur on the front half and foliate papillae on the sides at the back of the tongue. The actual taste buds occur in groups of two to 250 within the papillae.1 Each taste bud, in turn, consists of up to 100 cells, which are classified as either receptor, basal or supportive cells.1 Supporting cells contain microvilli and are thought to secrete substances into lumen of taste buds. Receptor cells are sensitive to different chemical substances that are interpreted as one of five tastes. Basal cells differentiate into new receptor cells as well as helping to pass this sensory information on to the brain. They are derived from surrounding epithelium and are continuously renewed approximately every 10 days.1 Taste buds are not confined to the tongue, but also occur on the walls of the mouth, the palates and even in the back of the larynx and epiglottis. These nonlingual taste buds are more common in children, but are still found in adults.2 Tiny taste organs or taste buds are scattered over the entire surface of the papillae, with large numbers concentrated on the circumvallate papillae, toward the middle of the tongue. Other types of papillae include the filiform papillae that occur along the border of the tongue and the fungiform or mushroom-shared papillae that occur on the front half and foliate papillae on the sides at the back of the tongue. The actual taste buds occur in groups of two to 250 within the papillae.1 Each taste bud, in turn, consists of up to 100 cells, which are classified as either receptor, basal or supportive cells.1 Supporting cells contain microvilli and are thought to secrete substances into lumen of taste buds. Receptor cells are sensitive to different chemical substances that are interpreted as one of five tastes. Basal cells differentiate into new receptor cells as well as helping to pass this sensory information on to the brain. They are derived from surrounding epithelium and are continuously renewed approximately every 10 days.1 Taste buds are not confined to the tongue, but also occur on the walls of the mouth, the palates and even in the back of the larynx and epiglottis. These nonlingual taste buds are more common in children, but are still found in adults.2

16. Innervations of the Tongue1,2 Innervations by: Chorda tympani (cranial nerve VII) Glossopharyngeal (cranial nerve IX) Loss of innervation results in loss of sensation. The two sides of the tongue are independently innervated: the chorda tympani - a branch of the facial or VIIth cranial nerve, innervates the anterior two-thirds and the glossopharyngeal - IXth cranial nerve, innervates the posterior one-third. During embryonic development tongue epithelial cells are modified into taste buds only after they have been innervated. At any stage of life, taste buds may degenerate upon denervation.2The two sides of the tongue are independently innervated: the chorda tympani - a branch of the facial or VIIth cranial nerve, innervates the anterior two-thirds and the glossopharyngeal - IXth cranial nerve, innervates the posterior one-third. During embryonic development tongue epithelial cells are modified into taste buds only after they have been innervated. At any stage of life, taste buds may degenerate upon denervation.2

17. Taste Maps3, 4 Taste buds are organized by region. But each region may contain several types of taste buds. Classic taste maps are an oversimplification. The classical taste map, found in so many introductory biology textbooks, showing different taste sensations associated with different regions of the tongue is now known to be an over-simplification. Despite what most of us learned in introductory biology classes, sensitivity to all tastes is distributed across the whole tongue and indeed to other regions of the mouth where there are taste buds such as on the epiglottis and soft palate, although with variable efficiency.3 The traditional taste maps, found in most textbooks showing large regional differences in sensitivity across the human tongue, typically indicate that sweetness is detected by taste buds on the tip of the tongue, sourness on the sides, bitterness at the back and saltiness along the edges. The maps first appeared in the early 20th century as a result of an oversimplification of research conducted in the late 1800s, and they have been almost impossible to purge from the literature despite researchers having known for many years that they are imprecise. Although there is increasing agreement that taste buds are not uniformly programmed to just detect one taste, it is not clear whether multiple taste sensitivity is due to different cells within the taste bud, or to multiple biochemical pathways, which are distinct, within the same cells.4 For example, although sensitivity to NaCl or salt is greatest in the fungiform papillae that are concentrated on the anterior tip and anterior lateral margins of the human tongue, taste buds in the same papillae are also sensitive to sucrose or sweet. Likewise, bitter receptors are not uniformly distributed over the tongue. Alpha-gustducin, which is the G-protein receptor coupled to the bitter receptors, occurs more commonly in circumvallate than fungiform papillae, but is found in both. The classical taste map, found in so many introductory biology textbooks, showing different taste sensations associated with different regions of the tongue is now known to be an over-simplification. Despite what most of us learned in introductory biology classes, sensitivity to all tastes is distributed across the whole tongue and indeed to other regions of the mouth where there are taste buds such as on the epiglottis and soft palate, although with variable efficiency.3 The traditional taste maps, found in most textbooks showing large regional differences in sensitivity across the human tongue, typically indicate that sweetness is detected by taste buds on the tip of the tongue, sourness on the sides, bitterness at the back and saltiness along the edges. The maps first appeared in the early 20th century as a result of an oversimplification of research conducted in the late 1800s, and they have been almost impossible to purge from the literature despite researchers having known for many years that they are imprecise. Although there is increasing agreement that taste buds are not uniformly programmed to just detect one taste, it is not clear whether multiple taste sensitivity is due to different cells within the taste bud, or to multiple biochemical pathways, which are distinct, within the same cells.4 For example, although sensitivity to NaCl or salt is greatest in the fungiform papillae that are concentrated on the anterior tip and anterior lateral margins of the human tongue, taste buds in the same papillae are also sensitive to sucrose or sweet. Likewise, bitter receptors are not uniformly distributed over the tongue. Alpha-gustducin, which is the G-protein receptor coupled to the bitter receptors, occurs more commonly in circumvallate than fungiform papillae, but is found in both.

18. Salivary Glands Major and Minor Salivary Glands Produce and secrete saliva Three pairs of major glands: Parotid Submaxillary Sublingual Over 1000 minor glands Buccal, palatal, lingual Salivary Glands: In humans, there are three pairs of major plus numerous minor salivary glands. The parotid glands, the largest pair of salivary glands, are situated just below and in front of each ear, the submandibular glands are below the jaw and the sublingual glands are under the tongue. Ducts carry the secretions of the salivary glands into the mouth cavity. Together with the mucus secreted by the membrane of the mouth and the secretions of other small glands in the mouth, saliva helps to keep the mouth moist, softens the food as it is chewed, and initiates the process of digestion by means of salivary amylase, the digestive enzyme contained in saliva, which converts starch to sugar. The flow of saliva is stimulated by the presence of food in the mouth, or even the sight and smell of food. A lack of salivary flow from a gland may be caused by the formation of a calculus, or mineral concretion, that blocks a duct. The parotid glands are subject to growths, usually benign, and to infection, such as the mumps. Salivary Glands: In humans, there are three pairs of major plus numerous minor salivary glands. The parotid glands, the largest pair of salivary glands, are situated just below and in front of each ear, the submandibular glands are below the jaw and the sublingual glands are under the tongue. Ducts carry the secretions of the salivary glands into the mouth cavity. Together with the mucus secreted by the membrane of the mouth and the secretions of other small glands in the mouth, saliva helps to keep the mouth moist, softens the food as it is chewed, and initiates the process of digestion by means of salivary amylase, the digestive enzyme contained in saliva, which converts starch to sugar. The flow of saliva is stimulated by the presence of food in the mouth, or even the sight and smell of food. A lack of salivary flow from a gland may be caused by the formation of a calculus, or mineral concretion, that blocks a duct. The parotid glands are subject to growths, usually benign, and to infection, such as the mumps.

19. Major Salivary Glands Parotid � below and anterior to the ear Submandibular � below the mandible Sublingual � anterior floor of the mouth Orifices / ducts: Stensen�s duct - parotid Wharton�s duct - submandibular Numerous small ducts of Sublingual glands Major Salivary Glands: Parotid glands are located below and in front of the external ear. Submandibular glands lie below the mandible and Sublingual glands, the smallest of the three main sets of glands, are found in a fold of mucous membrane in the anterior floor of the mouth, under the tongue. Orifices of these glands lie at the boundary of the mouth and the surrounding tissues: Stensen's duct, the orifice of the parotid gland, emerges at the Parotid papilla in the buccal mucosa opposite the upper second molars. This is often incorrectly referred to as Stenson�s duct. Wharton�s or Submandibular duct, the orifice of the submandibular glands, is in the anterior floor of mouth on the sublingual papilla adjacent to the lingual frenulum. Numerous, small orifices of the sublingual glands, some of which may unite with the submanibular duct beneath the tongue. Major Salivary Glands: Parotid glands are located below and in front of the external ear. Submandibular glands lie below the mandible and Sublingual glands, the smallest of the three main sets of glands, are found in a fold of mucous membrane in the anterior floor of the mouth, under the tongue. Orifices of these glands lie at the boundary of the mouth and the surrounding tissues: Stensen's duct, the orifice of the parotid gland, emerges at the Parotid papilla in the buccal mucosa opposite the upper second molars. This is often incorrectly referred to as Stenson�s duct. Wharton�s or Submandibular duct, the orifice of the submandibular glands, is in the anterior floor of mouth on the sublingual papilla adjacent to the lingual frenulum. Numerous, small orifices of the sublingual glands, some of which may unite with the submanibular duct beneath the tongue.

20. Minor Salivary Glands Numerous - can be > 1,000 Microscopic Scattered Buccal - inside of lips and cheeks Palatal - roof of mouth Lingual - tongue, around circumvalate papillae Not all in mouth proper, also in the larynx and epiglottis Minor Salivary Glands: The minor salivary glands are small, microscopic, glands that may number over 1000. Although they are not organized like the major salivary glands are, they are usually referred to by their location in the mouth: inside the lips (buccal), on the soft palate (palatal) or on the tongue (lingual), where they are most abundant in the trenches that surround the circumvalate papillae. � Minor Salivary Glands: The minor salivary glands are small, microscopic, glands that may number over 1000. Although they are not organized like the major salivary glands are, they are usually referred to by their location in the mouth: inside the lips (buccal), on the soft palate (palatal) or on the tongue (lingual), where they are most abundant in the trenches that surround the circumvalate papillae. �

21. Functions of the Mouth Articulation Digestion Mechanical Chemical Mastication Swallowing Functions of the Mouth: The lips, palates, tongue and teeth are the major components in the articulation of sound, speech, regulating air flow to produce consonants and interacting with the fundamental frequencies to produce the characteristic "sounds" of vowels. The process of digestion also begins in the mouth. Mechanical digestion, the chewing and grinding action of the teeth working with the tongue and cheeks, slide between teeth to hold the food between the occlusal surfaces of the teeth. This action reduces the food to a more readily digestible substance. Chemical digestion also begins in the mouth when the enzymatic process of converting starch to sugar is initiated by salivary amylase or ptyalin excreted by the salivary glands. As food is masticated and mixed with saliva, a bolus, a rounded mass of food, is formed. Placing the bolus on the back of the tongue and pharynx initiates the swallowing reflex. The swallowing center in the medulla oblongata is responsible for the complicated swallowing reflex. Functions of the Mouth: The lips, palates, tongue and teeth are the major components in the articulation of sound, speech, regulating air flow to produce consonants and interacting with the fundamental frequencies to produce the characteristic "sounds" of vowels. The process of digestion also begins in the mouth. Mechanical digestion, the chewing and grinding action of the teeth working with the tongue and cheeks, slide between teeth to hold the food between the occlusal surfaces of the teeth. This action reduces the food to a more readily digestible substance. Chemical digestion also begins in the mouth when the enzymatic process of converting starch to sugar is initiated by salivary amylase or ptyalin excreted by the salivary glands. As food is masticated and mixed with saliva, a bolus, a rounded mass of food, is formed. Placing the bolus on the back of the tongue and pharynx initiates the swallowing reflex. The swallowing center in the medulla oblongata is responsible for the complicated swallowing reflex.

22. Salivary Gland Function Innervation by both sympathetic and parasympathetic divisions of the autonomic nervous system. Saliva production affected by: Chewing Taste, smell or even thought of food Emotions like fear, anxiety and mental effort Dehydration Sleep The salivary glands are innervated by both the parasympathetic and sympathetic divisions of the Autonomic Nervous System: Parasympathetic stimulation causes vasodialation and increases saliva flow, while sympathetic stimulation causes vasoconstriction and decreases saliva flow. Saliva production is stimulated by chewing, sour taste, smell of food, or even the thought of or expectation of certain foods. In dogs, this is a conditioned reflex as demonstrated by the classical experiment of Pavlov. Whether this is also true in humans is not known. Saliva production is decreased by emotions such as fear, anxiety, mental effort and dehydration. During sleep, saliva production stops. Salivation is initiated by the salivary centers in the medulla oblongata, which receive afferent signals from the sensory neurons of the oral and nasal cavities and from the higher centers in the brain. The presence of food in the mouth or even the thought of certain types of food will stimulate salivation. Water and electrolyte secretion are mainly controlled by parasympathetic activity. Whereas, protein synthesis and secretion are mainly controlled by sympathetic activity. The salivary glands are innervated by both the parasympathetic and sympathetic divisions of the Autonomic Nervous System: Parasympathetic stimulation causes vasodialation and increases saliva flow, while sympathetic stimulation causes vasoconstriction and decreases saliva flow. Saliva production is stimulated by chewing, sour taste, smell of food, or even the thought of or expectation of certain foods. In dogs, this is a conditioned reflex as demonstrated by the classical experiment of Pavlov. Whether this is also true in humans is not known. Saliva production is decreased by emotions such as fear, anxiety, mental effort and dehydration. During sleep, saliva production stops. Salivation is initiated by the salivary centers in the medulla oblongata, which receive afferent signals from the sensory neurons of the oral and nasal cavities and from the higher centers in the brain. The presence of food in the mouth or even the thought of certain types of food will stimulate salivation. Water and electrolyte secretion are mainly controlled by parasympathetic activity. Whereas, protein synthesis and secretion are mainly controlled by sympathetic activity.

23. Saliva5 Moistens and lubricates Salivary amylase Bacteriostatic properties Maintenance of homeostasis on dental surfaces: Dissolves and dilutes metabolites Maintains proper pH balance Reduces plaque Saliva has multiple essential functions in relation to the digestive process taking place in the upper parts of the gastrointestinal (GI) tract. Saliva functions indirectly in the digestive process through the maintenance of an intact dentition and mucosa. Saliva moistens and lubricates the food, buffers it with bicarbonate and dissolves it which is necessary for taste. There is a bacteriostatic function and a continual washing of the mouth also provided by saliva. Finally, the salivary glands also assist in the excretion of heavy metals and inorganic and organic materials.5 The maintenance of homeostasis on the dental surfaces as well as in the entire oral cavity is highly dependent on the composition of saliva, especially the presence of inorganic compounds such as bicarbonate and multiple proteins. Whole saliva is a mixture of the secretions from the various salivary glands and gingival crevicular fluid. It contains various defense mechanisms, including leukocytes, secretory IgA, agglutinating proteins and a number of enzymes which bathe the actual sites of microbial growth on the tooth and mucosal surfaces.5 Saliva dilutes and carries away metabolites diffusing out of any microorganisms on or about the dental surfaces called dental plaque. Secondly, it supplies bicarbonate ions which diffuse into the plaque and neutralize the by-products of fermentation or organic acids in situ.5 Saliva has multiple essential functions in relation to the digestive process taking place in the upper parts of the gastrointestinal (GI) tract. Saliva functions indirectly in the digestive process through the maintenance of an intact dentition and mucosa. Saliva moistens and lubricates the food, buffers it with bicarbonate and dissolves it which is necessary for taste. There is a bacteriostatic function and a continual washing of the mouth also provided by saliva. Finally, the salivary glands also assist in the excretion of heavy metals and inorganic and organic materials.5 The maintenance of homeostasis on the dental surfaces as well as in the entire oral cavity is highly dependent on the composition of saliva, especially the presence of inorganic compounds such as bicarbonate and multiple proteins. Whole saliva is a mixture of the secretions from the various salivary glands and gingival crevicular fluid. It contains various defense mechanisms, including leukocytes, secretory IgA, agglutinating proteins and a number of enzymes which bathe the actual sites of microbial growth on the tooth and mucosal surfaces.5 Saliva dilutes and carries away metabolites diffusing out of any microorganisms on or about the dental surfaces called dental plaque. Secondly, it supplies bicarbonate ions which diffuse into the plaque and neutralize the by-products of fermentation or organic acids in situ.5

24. Saliva and Plaque6 Enamel is hardest tissue in the body formed only before tooth eruption. May be dissolved by acids from foods or produced by bacteria resulting in caries. Saliva washes away microbes. Saliva neutralizes acids or bicarbonate. Dental enamel is the hardest tissue in the human body, and the main challenge to it comes from acidic conditions in the oral cavity which can cause dissolving of the mineral or dental caries or erosion. The metabolism of the microbial flora on the dental surfaces produces considerable amounts of acid, mainly in the form of lactic, acetic, formic and propionic acids. Moreover, various foods and drinks add to the acidity on these surfaces. Acid neutralization by bicarbonate is accelerated by salivary carbonic anhydrase which has been shown to play a remarkable role in protecting teeth from caries. This is secreted by acinar cells of the parotid and submandibular glands and is the only example of a secreted carbonic anhydrase in mammals.6 Dental enamel is the hardest tissue in the human body, and the main challenge to it comes from acidic conditions in the oral cavity which can cause dissolving of the mineral or dental caries or erosion. The metabolism of the microbial flora on the dental surfaces produces considerable amounts of acid, mainly in the form of lactic, acetic, formic and propionic acids. Moreover, various foods and drinks add to the acidity on these surfaces. Acid neutralization by bicarbonate is accelerated by salivary carbonic anhydrase which has been shown to play a remarkable role in protecting teeth from caries. This is secreted by acinar cells of the parotid and submandibular glands and is the only example of a secreted carbonic anhydrase in mammals.6

25. Taste7 Fine Taste vs. Crude Taste Five flavors: Sweet Salty Sour Bitter Umami Non-conventional taste stimuli such as fatty acids, metals or other minerals Trigeminal sense like heat or mouth feel Gustatory function consists of three different aspects: Fine taste that helps to distinguish between similar foods and is predominately an olfactory function. Crude taste distinguishing sweet from sour and is mediated through the taste buds. Because of the localization of most taste buds on the tongue, crude taste is also known as lingual taste. The taste buds, located on the tongue, have openings which receive the molecules and ions present in foods once they have dissolved in the saliva and then, sends them to the receptor cells below the surface, registering them as flavors or what is referred to as the tastes of sweet, salty, sour and bitter. Many recent studies also describe a fifth taste sensation called umami or hearty, a response to glutamic acid such as monosodium glutamate, aspartic acid, and other amino acids. Other taste qualities may include fatty, metallic from iron components in medicines and chalky from calcium salts. Last, there is a third chemical sensor working alongside smell and taste, known as the trigeminal sense. Trigeminal or cranial nerve V endings in the tongue and oral cavity are sensitive to the pungent chemicals given off by such hot spices as chili peppers or capsaicin, black pepper or piperine, mustards and horseradish or isothiocyanates, and onions or diallyl sulfide. They also respond to cool spices, such as mint ormenthol, and to the chemical bite or sharpness of ethyl alcohol in tequila and rum. In each of these cases, our trigeminal nerve endings respond to chemical irritants rather than to gustatory taste cues per se which are sensed instead by the facial cranial VII and glossopharyngeal cranial IX nerves. Trigeminal taste is an important ingredient in many, perhaps in most, of the world's cuisines as humans have a seemingly indispensable need for trigeminal stimulation at mealtime. The trigeminal sense also produces what is referred to as mouth feel such as effervescence, crunchiness and texture of food or beverages and thermal stimulation like the hotness of coffee or tea or the coolness of an iced drink. Why humans crave trigeminal stimulation in foods, beverages and oral-care products such as mint-flavored mouthwashes, toothpicks and toothpastes is a mystery. The trigeminal sense is basically a pain response. It has been suggested that the capsaicin in chili peppers works to release endorphins, opium-like substances which produce pleasure cues in the brain. Or perhaps we like the thrill of culinary danger, after all many people willingly pay $200 or more to eat dishes prepared from the poisonous fugu pufferfish, despite nearly the 100 deaths that occur every year. An old Japanese saying perhaps explains such curious behavior best, "Those who eat fugu are stupid. But those who don't eat fugu are also stupid.� 7Gustatory function consists of three different aspects: Fine taste that helps to distinguish between similar foods and is predominately an olfactory function. Crude taste distinguishing sweet from sour and is mediated through the taste buds. Because of the localization of most taste buds on the tongue, crude taste is also known as lingual taste. The taste buds, located on the tongue, have openings which receive the molecules and ions present in foods once they have dissolved in the saliva and then, sends them to the receptor cells below the surface, registering them as flavors or what is referred to as the tastes of sweet, salty, sour and bitter. Many recent studies also describe a fifth taste sensation called umami or hearty, a response to glutamic acid such as monosodium glutamate, aspartic acid, and other amino acids. Other taste qualities may include fatty, metallic from iron components in medicines and chalky from calcium salts. Last, there is a third chemical sensor working alongside smell and taste, known as the trigeminal sense. Trigeminal or cranial nerve V endings in the tongue and oral cavity are sensitive to the pungent chemicals given off by such hot spices as chili peppers or capsaicin, black pepper or piperine, mustards and horseradish or isothiocyanates, and onions or diallyl sulfide. They also respond to cool spices, such as mint ormenthol, and to the chemical bite or sharpness of ethyl alcohol in tequila and rum. In each of these cases, our trigeminal nerve endings respond to chemical irritants rather than to gustatory taste cues per se which are sensed instead by the facial cranial VII and glossopharyngeal cranial IX nerves. Trigeminal taste is an important ingredient in many, perhaps in most, of the world's cuisines as humans have a seemingly indispensable need for trigeminal stimulation at mealtime. The trigeminal sense also produces what is referred to as mouth feel such as effervescence, crunchiness and texture of food or beverages and thermal stimulation like the hotness of coffee or tea or the coolness of an iced drink. Why humans crave trigeminal stimulation in foods, beverages and oral-care products such as mint-flavored mouthwashes, toothpicks and toothpastes is a mystery. The trigeminal sense is basically a pain response. It has been suggested that the capsaicin in chili peppers works to release endorphins, opium-like substances which produce pleasure cues in the brain. Or perhaps we like the thrill of culinary danger, after all many people willingly pay $200 or more to eat dishes prepared from the poisonous fugu pufferfish, despite nearly the 100 deaths that occur every year. An old Japanese saying perhaps explains such curious behavior best, "Those who eat fugu are stupid. But those who don't eat fugu are also stupid.� 7

26. Taste Reception8,9 Different taste molecules or tastants received differently Different taste buds sensitive to more than one type of tastant Probably considerable overlap among different taste buds The actual mechanisms of sensitivity and transduction or the mechanism by which a sensory stimulus is converted into a nervous impulse differ. For each taste, however there is increasing evidence that individual taste qualities may use more than one mechanism.8,9The actual mechanisms of sensitivity and transduction or the mechanism by which a sensory stimulus is converted into a nervous impulse differ. For each taste, however there is increasing evidence that individual taste qualities may use more than one mechanism.8,9

27. Taste Mechanisms-Sweet10,11 Membrane receptor binds tastant. cAMP levels elevated by second messenger. PKA-mediated phosphorylation of K+ channels. Membrane depolarization allows Ca ++ entry. Gustducin activation in receptor cell transmitter to basal cells. Transmitter substance released by receptor cell via basal cells initiates nervous signals to brain. Sweet and some bitter taste stimuli activate a chemical messenger known as gustducin. Sweet taste is modulated by membrane receptors that bind or recognize glucose and other carbohydrates such as sucrose, saccharin, dulcin and acesulfame-K.10 Several amino acids taste have a sweet as well as umami taste to humans.11 Binding of the receptor activates an enzyme, adenylyl cyclase, that is also found in the cell membrane thereby, elevating cAMP in the interior of the cell. This is an example of what is known as a second messenger mediated response whereby a molecule too large to normally enter the cell, as is the case of sucrose, can affect changes inside the cell through the production or activation of a second molecule, the Second messenger. This causes a PKA-mediated phosphorylation of K+ channels, inhibiting them. Depolarization of the cell membrane occurs, allowing Ca2+ to enter the cell. Eventually, a transmitter substance release occurs from the receptor cell, resulting in an increased rate of nervous signals in the primary afferent nerve. Sweet and some bitter taste stimuli activate a chemical messenger known as gustducin. Sweet taste is modulated by membrane receptors that bind or recognize glucose and other carbohydrates such as sucrose, saccharin, dulcin and acesulfame-K.10 Several amino acids taste have a sweet as well as umami taste to humans.11 Binding of the receptor activates an enzyme, adenylyl cyclase, that is also found in the cell membrane thereby, elevating cAMP in the interior of the cell. This is an example of what is known as a second messenger mediated response whereby a molecule too large to normally enter the cell, as is the case of sucrose, can affect changes inside the cell through the production or activation of a second molecule, the Second messenger. This causes a PKA-mediated phosphorylation of K+ channels, inhibiting them. Depolarization of the cell membrane occurs, allowing Ca2+ to enter the cell. Eventually, a transmitter substance release occurs from the receptor cell, resulting in an increased rate of nervous signals in the primary afferent nerve.

28. Taste Mechanisms-Bitter12-14 Tastant binding affects different second messenger � IP3 Internal Ca ++ stores initiate release of transmitter substance Similar pattern of gustducin activation Many bitter or alkaline substances poisonous Bitter substances, chiefly alkaline molecules, cause a different second messenger, inositol trisphosphate (IP3). Mediated release of Ca2+ from internal stores, external Ca2+ is not required. The elevated Ca2+ causes transmitter release, and this increases the firing of the primary afferent nerve. Since many naturally occurring poisons are bitter, our aversion to bitter tastes may be innate.12 In either case, the activation of gustducin initiates an electrochemical exchange among the receptor cells, which then transmit their messages to the basal cells at the bottom of the bud. The basal cells can also talk back to the receptor cells, principally through the production of seratonin, a transmitter substance which functions to increase receptor cell sensitivity.13,14 Bitter substances, chiefly alkaline molecules, cause a different second messenger, inositol trisphosphate (IP3). Mediated release of Ca2+ from internal stores, external Ca2+ is not required. The elevated Ca2+ causes transmitter release, and this increases the firing of the primary afferent nerve. Since many naturally occurring poisons are bitter, our aversion to bitter tastes may be innate.12 In either case, the activation of gustducin initiates an electrochemical exchange among the receptor cells, which then transmit their messages to the basal cells at the bottom of the bud. The basal cells can also talk back to the receptor cells, principally through the production of seratonin, a transmitter substance which functions to increase receptor cell sensitivity.13,14

29. Taste Mechanisms -Salty and Sour15 Salt ions directly enter receptor cells Affect membrane depolarization Calcium entry Release of transmitter substance Salty and sour molecules permeating the taste cells directly through special channels in their walls. Salt is sodium chloride (Na+ Cl-). Na+ ions enter the receptor cells via Na-channels causing a depolarization that allows Ca2+ to enter through voltage-sensitive Ca2+ channels. Sour taste is a sensitivity to acids, particularly the hydrogen ions (H+) produced by acids. H+ ions block K+ channels that are responsible for maintaining the cell membrane at its resting potential of approximately -85mV. Blocking these channels also results in membrane depolarization, followed by Ca2+entry, transmitter substance release and increases nervous activity in the primary afferent neurons.15Salty and sour molecules permeating the taste cells directly through special channels in their walls. Salt is sodium chloride (Na+ Cl-). Na+ ions enter the receptor cells via Na-channels causing a depolarization that allows Ca2+ to enter through voltage-sensitive Ca2+ channels. Sour taste is a sensitivity to acids, particularly the hydrogen ions (H+) produced by acids. H+ ions block K+ channels that are responsible for maintaining the cell membrane at its resting potential of approximately -85mV. Blocking these channels also results in membrane depolarization, followed by Ca2+entry, transmitter substance release and increases nervous activity in the primary afferent neurons.15

30. Taste Mechanisms - Umami15 Response to certain amino acids such as glutamate, aspartate and related compounds First identified in Japan Metabotropic glutamate receptor (mGluR4) mediates umami taste Binding to the receptor activates a G-protein elevating intracellular Ca2+ Monosodium glutamate may stimulate the umami receptors Additional ionotropic glutamate receptors (NMDA-receptor) also present Umami is the taste of certain amino acids such as glutamate, aspartate and related compounds. It was first identified by Kikunae Ikeda at the Imperial University of Tokyo in 1909. Recently, it has been shown that the metabotropic glutamate receptor (mGluR4) mediates umami taste. Binding to the receptor activates a G-protein, and this may elevate intracellular Ca2+. Monosodium glutamate, added to many foods to enhance their taste and the main ingredient of soy sauce, may stimulate the umami receptors. But, in addition, there are ionotropic, linked to ion channels, glutamate receptors, such as the NMDA-receptor on the tongue. When activated by these umami compounds or soy sauce, non-selective cation channels open, thereby, depolarizing the cell. Calcium enters, causing transmitter release and increased firing in the primary afferent nerve.15Umami is the taste of certain amino acids such as glutamate, aspartate and related compounds. It was first identified by Kikunae Ikeda at the Imperial University of Tokyo in 1909. Recently, it has been shown that the metabotropic glutamate receptor (mGluR4) mediates umami taste. Binding to the receptor activates a G-protein, and this may elevate intracellular Ca2+. Monosodium glutamate, added to many foods to enhance their taste and the main ingredient of soy sauce, may stimulate the umami receptors. But, in addition, there are ionotropic, linked to ion channels, glutamate receptors, such as the NMDA-receptor on the tongue. When activated by these umami compounds or soy sauce, non-selective cation channels open, thereby, depolarizing the cell. Calcium enters, causing transmitter release and increased firing in the primary afferent nerve.15

31. Biography Richard H. Moore is a Professor in the Department of Biology at Coastal Carolina University in Conway, SC. He received his PhD in Marine Zoology from the University of Texas at Austin in 1973, and since 1974, has been employed at CCU where he currently holds the position of Assistant Vice President for Grants and Sponsored Research. He is an author of Fishes of the Gulf of Mexico: Texas, Louisiana and Adjacent Waters as well as research papers and book chapters in the fields of ecology and physiology. He has taught or currently teaches courses in Human Anatomy and Physiology, Comparative Physiology, Ichthyology, Aquaculture, Vertebrate Zoology and the Biology of Human Aging.