seminar 3 - physiology MASTICATION AND DEGLUTITION

Mastication is the initial stage in the process of digestion, whereby the food placed in the mouth is cut and ground into smaller pieces, mixed with saliva and made into a bolus for easier swallowing.
Especially important for raw vegetables and fruits, because these have indigestible cellulose membranes around their nutrient portions.
Increases the surface area of food, thereby enhancing the action of digestive enzymes.

Facilitates solubilization of food substances in saliva to stimulate taste receptors and provide lubrication for easy swallowing.
The active components of mastication are the reflexly controlled and coordinated muscles whose contraction results in rhythmic movements of the passive parts of masticatory (stomatognathic) system – namely the mandible, the temperomandibular joint and the teeth.
They carry out a wide range of functions. On the one hand, they are able to move the mandible with a high degree of precision to enable speech. On the other hand, they are able to exert enormous forces that are required to break down tough foods.
They develop from the mesoderm of the first branchial arch and are supplied by the mandibular nerve
The four muscles of mastication are

MASSETER
MEDIAL PTERYGOID
LATERAL PTERYGOID AND
TEMPORALIS
Superficial Layer
It is the largest component that arises from the anterior two thirds of the lower border of the zygomatic arch
Insertion
Lower part of lateral surface of ramus of mandible

1. PHYSIOLOGY OF MASTICATION AND DEGLUTITION DR. NOORI I MDS

2. contents Introduction Muscles of Mastication TMJ Mandibular movements in mastication Physiology of Mastication Saliva Reflexes Deglutition Disorders Conclusion References

3. Introduction   Mastication is the initial stage in the process of digestion, whereby the food placed in the mouth is cut and ground into smaller pieces, mixed with saliva and made into a bolus for easier swallowing. Especially important for raw vegetables and fruits, because these have indigestible cellulose membranes around their nutrient portions.

4. Increases the surface area of food, thereby enhancing the action of digestive enzymes. Facilitates solubilization of food substances in saliva to stimulate taste receptors and provide lubrication for easy swallowing.

5. FUNCTIONAL ANATOMY OF COMPONENTS OF MASTICATION The active components of mastication are the reflexly controlled and coordinated muscles whose contraction results in rhythmic movements of the passive parts of masticatory ( stomatognathic ) system – namely the mandible, the temperomandibular joint and the teeth.

6. MUSCLES OF MASTICATION They carry out a wide range of functions. On the one hand, they are able to move the mandible with a high degree of precision to enable speech. On the other hand, they are able to exert enormous forces that are required to break down tough foods. They develop from the mesoderm of the first branchial arch and are supplied by the mandibular nerve.

7. The four muscles of mastication are MASSETER MEDIAL PTERYGOID LATERAL PTERYGOID AND TEMPORALIS

8. Superficial Layer It is the largest component that arises from the anterior two thirds of the lower border of the zygomatic arch Insertion Lower part of lateral surface of ramus of mandible MASSETER (superficial)

9. Origin Anterior 2/3 rd of deep surface and posterior 1/3 rd of lower border of zygomatic arch Insertion Middle part of ramus MASSETER (middle)

10. Origin Deep layer arises from the whole length of medial surface of zygomatic arch Insertion ramus and coronoid process of mandible MASSETER (deep)

11. NERVE SUPPLY: masseteric nerve, branch of anterior division of mandibular nerve ACTION: Elevates mandible to close mouth and clenches teeth

12. It is a fan shaped muscle that fills the temporal fossae ORIGIN: Floor of temporal fossa(inferior temporal line) overlying temporal fascia of the side of skull INSERTION: Deep surface of coronoid process ,anterior border of ramus of mandible NERVE SUPPLY: Deep temporal nerve, branch of anterior division of mandibular nerve ACTION : Elevates mandible. Retracts protruded mandible . TEMPORALIS

13. ORIGIN Infratemporal surface and crest of greater wing of sphenoid INSERTION Pterygoid fovea LATERAL PTERYGOID (upper head)

14. ORIGIN: Lateral surface of lateral pterygoid plate INSERTION: Anterior margin of articular disc and capsule of TMJ LATERAL PTERYGOID (lower head)

15. NERVE SUPPLY: Branch from anterior division of mandibular nerve ACTION: Depresses mandible along with suprahyoid muscles. Lateral and medial pterygoid act together to protrude the mandible. Lateral and medial pterygoid act alternatively to produce side to side movement as in chewing

16. ORIGIN: Maxillary tuberosity INSERTION: Roughened area on the medial surface of angle and adjoining ramus of mandible MEDIAL PTERYGOID (superficial head)

17. ORIGIN  : Medial surface of the Lateral plate of Pterygoid process and Pyramidal process of Palatine bone INSERTION: Roughened area on the medial surface of angle and adjoining ramus of mandible MEDIAL PTERYGOID (deep head)

18. NERVE SUPPLY: Nerve to medial pterygoid , a branch of main trunk of mandibular nerve ACTION: Elevates mandible Help protrude mandible Right medial pterygoid with left lateral pterygoid turn the chin to left side

19. THE TEMPOROMANDIBULAR JOINT This is a synovial joint of the condylar variety. NERVE SUPPLY: a) Auricular nerve b) Masseteric nerve

20. The upper articular surface formed by following parts of temporal bone (a) articular eminence & (b) mandibular fossa . The lower articular surface is formed by the head of mandible. The articular surfaces are covered with fibrocartilage . The joint cavity is divided into upper and lower compartments by the intra- articular disc.

21. The upper compartment permits gliding movements & lower rotatory as well as gliding movements. The disc has a concavo-convex upper surface and a concave lower surface. The TMJ is reinforced by ligaments, namely the fibrous capsule, the lateral ligament, the sphenomandibular ligament and the stylomandibular ligament.

22. TEETH

23. In man, teeth are diphyodont ; the first set of teeth called as milk or deciduous teeth, and the second set as permanent teeth. The deciduous teeth are 20 in number. The permanent teeth are 32 in number. The shape of the tooth is adapted to its function. Incisors are cutting teeth, with chisel like crowns. The upper and lower teeth overlap each other like blades of a pair of scissors. Canines are holding and tearing teeth, with conical crowns. These are better developed in carnivores. Premolars and molars are grinding teeth, bearing 4-5 cusps on their crowns

24. MANDIBULAR MOVEMENTS OF MASTICATION

25. Primate (mammalian) mastication is characterized by two distinct stages, which leave characteristic wear facets. During Phase I, the teeth are brought into occlusion and the food is predominantly sheared and crushed, whereas grinding occurs mainly during Phase II of mastication

26. PHYSIOLOGY OF MASTICATION Mastication is brought about by voluntary muscles, and it is possible, therefore, for it to be controlled entirely by will; but like other complicated muscular activities, its control is normally exercised by sub-cortical centres . Three possibilities have been suggested about reflex control of mastication.

27. when the jaw is closed voluntarily on a piece of food, the force applied to the gums, teeth & hard palate provides a stimulus for the jaw opening reflex & reflexly inhibits the jaw closing muscles. The jaw opening then causes a rebound of original jaw closing reflex which is followed by a repetition of whole cycle until the masticated material is removed

28. Rhythm originates from cerebral cortex or some sub cortical centre. Different types of movement of jaw, mostly contralateral but some ipsilateral are produced by stimulating different cortical areas. Some areas of brain stem act as a ‘pattern generator’ which may send out rhythmic impulses in response either to cortical or intra oral stimuli.

29. PHASES OF THE CHEWING CYCLE PREPARATORY PHASE. FOOD CONTACT PHASE. FOOD CRUSHING PHASE. TOOTH CONTACT PHASE.

30. PREPARATORY PHASE The chewing movement begins when the chewing pattern generator in the brain causes the jaw opening muscles to pull the mandible downwards from the rest or intercuspal position at about 7-8 cm/sec.

31. The jaw initially moves away from the working side as it begins to open, but then swings towards the working side. When the jaw is open, reflex inactivation of opening muscles occur; and activates the tongue and cheek muscles to position the food between the teeth

32. FOOD CONTACT PHASE The opening of the jaw causes stretch reflex of jaw muscles which in turn produces rebound contraction of jaw, closing muscles to produce the initial closing movement at about 10cm/sec. This traps the food between the teeth. Periodontal reflexes assist in grasping food in the correct position between the teeth, ready to be bitten through

33. FOOD CRUSHING PHASE The jaw closing muscles forces the teeth through the food bolus. Peak biting force during chewing is in the range of 50-100N, in the molar region.

34. TOOTH CONTACT PHASE Further activation of jaw closing muscles causes point of initial contact of opposing teeth. Teeth then slide from working side into the intercuspal position. This causes grinding of food into a paste.

35. When the mouth is closed buccal receptors and periodontal ligament receptors activated & reflex inhibition of jaw –closing muscles and reactivation of jaw opening muscles. Thus chewing cycle is repeated. Each chewing cycle takes about 0.8-1 seconds

36. THE MECHANICS OF MASTICATION The mechanics of mastication includes: The TMJ Muscles of mastication The role of tongue The hard palate The cheeks and lips Tooth movements in mastication The role of saliva .

37. THE TEMPOROMANDIBULAR JOINT In man, the TMJ allows 3 types of movements: First , hinge-like movement, for biting; Second possible movement protrusion & withdrawal , may be used in early phases of mastication. Third is the lateral movement, used during mastication proper & results in grinding of food. This is accompanied by vigorous hinge-like movements which cause crushing to occur along with grinding

38. THE MUSCLES OF MASTICATION The jaw opening muscles are lateral pterygoid, the digastric and the infrahyoid muscles The jaw closing muscles are : Temporalis: used in quick closure and gentle biting. masseter and medial pterygoid : used in more powerful crushing

39. THE ROLE OF TONGUE First it may have a direct crushing effect on food, by pressing it against the hard palate. Secondly, the tongue pushes the food onto the occluding surface of teeth, transfers it from one side to another, and helps to mix it in saliva.

40. Thirdly enable to select those parts of food mass which are sufficiently well masticated to be ready for swallowing & to separate them from parts requiring further mastication. After eating, sweeping movements help in removing food residue trapped between cheeks & gingivae & elsewher e

41. THE HARD PALATE Acts as a surface against which the tongue works Epithelial surface of the palate is very sensitive to touch. Food which is harsher than usual is detected mostly by this surface.

42. THE CHEEKS AND LIPS The cheeks press against the buccal surface of teeth and prevent food from pouching in the buccal vestibule. The function of lips are Sensory : their sensitivity to touch and temperature helps to prevent unsuitable material from entering the oral cavity Mechanical : helps in transfer of food & especially drink into mouth & in preventing the loss of food from mouth during mastication

43. TOOTH MOVEMENTS DURING MASTICATION During mastication slight movements of teeth occur, but one is not usually aware of them unless mastication is powerful. First phase occurs when periodontal fibres were stretched. The second phase represents an elastic deformation of the alveolar bone

44. Tooth mobility is highest soon after waking up; greater in children than in adults, is slightly greater in females than in males; incisors are more mobile than multi-rooted teeth. Movement varies with force in 2 phases, at first small forces cause relatively large movement but when the force exceeded a certain figure (higher than 100 g observed by Muhlemann ) the movement decreased.

45. STRUCTURE OF TERMINAL SECRETORY UNITS OF SALIVARY GLANDS Salivary glands are made up of cells which are arranged in small groups around a central globular cavity called acinus . The central cavity is continous with the lumen of the duct.

46. The fine duct draining each acinus is called the intercalated ducts. Many intercalated ducts join together to form intralobular ducts. Two or more intralobular ducts join to form interlobular ducts , which unite to form the main duct of the gland. The gland with this type of structure & duct system is called racemose type.

47. FORMATION OF SALIVA The secretory acinus produces the primary saliva, which is isotonic with an ionic composition resembling that of plasma. In the duct system, the primary saliva is then modified by selective reabsorption of Na+ and Cl - (without water) and secretion of K+ and HCO3- .

48. Salivary secretion is a two-stage process: Initial Formation stage  acini secrete a primary secretion that contains ptyalin and/or mucus in a solution of ions similar to plasma. Modification stage  is when the primary secretion flows through the ducts and the ionic composition of saliva is modified.

49. Initial Formation Stage: Stimulation of the parasympathetic nerve, or mainly muscarinic cholinergic receptors, initiates intracellular second messenger events of acinar cells the signal transduction system involves the release of Ca2+ from intracellular stores. The increase in intracellular Ca2+ levels leads to the Cl – channels at the apical membrane to open and an influx of Cl – into the lumen.

50. Hence the change in electronegativity by Cl – influx causes Na+ to diffuse across the cation -permeable tight junction between acinar cells to preserve electroneutrality within the lumen. The net influx of NaCl creates an osmotic gradient across the acinus , which draws water from the blood supply via a tight junction.  Thus, saliva secreted in the lumen (primary saliva) is an isotonic plasma-like fluid.

51. Modification Stage: The intralobular ducts reabsorb Na+ and Cl – excluding water, and make the final saliva hypotonic. Stimulation of the sympathetic nerve, or ß-adrenergic receptors, causes exocytosis but less fluid secretion. Activation of ß- adrenoceptors increases the intracellular cyclic adenosine monophosphate ( cAMP ) level, which is the primary second messenger for amylase secretion.

52. cAMP is thought to activate protein kinase which may regulate the process by which cells release the contents of their secretory granules. This involves the fusion of the granule membrane with the luminal plasma membrane of the secretory cell followed by rupture of the fused membranes. The released contents of granules comprise a wide variety of proteins which are unique to saliva and show biological functions of particular importance to oral health. 

53. COMPOSITION OF SALIVA saliva Water -99.5% solids 0.5% Organic substance Inorganic substance Gases Enzymes Other org. substance 1.amylase 2.maltase 3.lingual lipase 4.lysozyme 5.phosphatase 6.carbonic anhydrase 7.kalikrein 1.Proteins- mucin & albumin 2.Blood group antigen 3.Free amino acids 4.Non protein nitrogenous substances- urea,uric acid,creatinine,xanthine hypoxanthine 1.Sodium 2.Calcium 3.Potassium 4.Biocarbonate 5.Bromide 6.Chlorine 7.Fluoride 8.phosphate 1.Oxygen 2.Carbon dioxide 3.Nitrogen

54. THE ROLE OF SALIVA 1. Protective function: Dilutes hot and irritant food. Washes away food remnants. Dilutes any HCl and bile 2. In mastication: Aids in formation of bolus. Salivary mucous lubricates buccal mucosa and teeth.

55. 3. Digestive function: Action on carbohydrates By alpha-amylase or ptyalin. Acts on alpha 1-4 linkage of starch. Converts it to maltose. Boiled starch  erythrodextrin  achrodextrin  isomaltose  maltose Lingual lipase acts on triglyceride. 4. Role in taste sensation: Acts as a solvent for food stuffs; taste receptors respond only to dissolved substances .

56. NEURONAL CONTROL OF MASTICATION Mastication is neither purely voluntary, nor purely reflex. It is a cyclical movement. Involves the trigeminal system. Has got 2 components: The basic rhythm of cyclical movements is hard wired in the brain and is called the ‘ central pattern generator ’. It can occur without feedback. However, like voluntary movements, cyclical movements are fine tuned by sensory signals through reflexes .

57. CENTRAL CONTROL The trigeminal motor nucleus and their interconnections constitute the ‘central pattern generator’. Their activity can be generated from both the cortex and from sensory signals from the masticatory system

58. REFLEXES MODULATING THE MASTICATORY CYCLE Stretch reflex Periodontal reflex Tendon organ reflex Joint reflexes

59. STRETCH REFLEX Maintains the jaw in its ‘rest position’, especially during vigorous head movements. During mastication, when the jaw is opened, stretch reflex is activated reflex inhibition of jaw opening muscles activation of jaw closing muscles. The stretch reflex helps to adjust the force exerted by the jaw closing muscles. The jaw closing muscles are richly endowed with muscle spindles 

60. PERIODONTAL REFLEX These are reflexes which arise from receptors that lie around the teeth. They are directionally sensitive and give subjective sensation about pressure on teeth. 2 types: receptors in periodontal ligament signal smaller forces receptors in bony socket signal larger forces Two different periodontal reflexes in mastication:

61. Sudden snapping of teeth together causes rapid and profound inhibition of jaw closing muscles. This is a protective reflex On the other hand, weak pressure reflexly excites jaw closing muscles & increases muscle force. Helps to hold food in between the teeth. They also guide teeth into occlusion from the point of first contact & causes grinding of food

62. TENDON ORGAN REFLEXES Present in the junction of masticatory muscle fibers and tendons. Gives signal that is related to force exerted by the muscle. Role in mastication is not clearly understood. Probably monitors the force exerted by a number of different motor units during weak contractions. During stronger contractions their outputs become saturated.

63. JOINT REFLEXES There are 4 types of receptors Type 1: the most numerous in joint capsule are clusters of small globular corpuscles. They are of low threshold & slowly adapting, so that even when the mandible is at rest the tension is sufficient to excite them.They are principal sources of the impulses concerned with perception of mandibular position

64. Type 2: Encapsulated conical end organs which are stimulated briefly immediately after movement of joint. Type 3: High threshold responds only to excessive tension in the lateral ligament Type 4: Pain receptor consisting of free nerve endings and plexuses of unmyelinated fibers

65. DEGLUTITION Swallowing is a complicated mechanism, principally because the pharynx most of the time subserves several other functions besides swallowing and is converted for only a few seconds at a time into a tract for propulsion of food. It is especially important that respiration not be compromised because of swallowing.

66. Deglutition/Swallowing consists of a sequence of muscular contractions that propels ingested material and pooled saliva from the mouth to the stomach. It is a complex reflex mechanism; requiring the co-ordination of a large number of motor neurons. On an average swallowing occurs 1000 times per day – highest during eating and least during sleeping

67. Tongue : Intrinsic muscles- change its shape Extrinsic muscles- change its position in oral cavity and helps in chewing of food.

68. PREPARATORY STAGE When the food is ready for swallowing, it is voluntarily positioned on the dorsum of the tongue. The tongue is now like a spoon-like depression , with its Tip pressed against palatal aspect of upper incisors. lateral borders against the buccal teeth and palatal mucosa pharyngeal part arches up to meet the soft palate ,which pushes down , to keep the food bolus from escaping into the pharynx- called the ‘ glossopalatine sphincter ’.

69. ORAL STAGE(voluntary) The positioning of the food bolus on the tongue dorsum marks the beginning of the oral stage. To stabilize the mandible during swallow the lips seal and the teeth are brought closer together. The anterior 2/3 rd of tongue moves upward and backward to propel the food toward the pharynx. The base of tongue moves downward and forward to expand the hypopharynx. The palate moves upward to open the glossopalatine sphincter. From here on swallowing becomes entirely or almost entirely automatic and ordinarily cannot be stopped.

70. pharynx Wide muscular tube- 12x3.5cms Muscles: Stylopharyngeus-elevates larynx Salpingopharyngeus - elevates larynx Palatopharyngeus Constrictors: Superior- aids soft palate in closing nasopharynx, propels bolus downward Middle- propels bolus downward Inferior-propels bolus down and forms sphincter at lower end( cricopharyngeus )

71. PHARYNGEAL PHASE The pharyngeal phase starts when the posterior part of the tongue makes a rapid piston-like movement to propel the bolus into the pharynx. The food bolus stimulates swallowing receptor areas all around the opening of the pharynx, especially in the tonsillar pillars. These send impulses to the brain stem to initiate a series of automatic muscle contractions.

72. The entire pharyngeal stage occurs in less than 2 seconds . 1.Nasopharynx is closed by the upward movement of soft palate by tensor and levator palati (close posterior nares); preventing regurgitation of food into the nasal cavities. 2.The palatopharyngeal folds on either side of the pharynx are pulled medially to approximate each other. These folds form a sagittal slit through which the food must pass into posterior pharynx . Slits performs a selective action- allows food masticated sufficiently to pass through, while impeding passage of large objects

73. 3. Vocal cords of the larynx are strongly approximated, and larynx is pulled upward and anteriorly by the neck muscles. Epiglottis swings backward over opening of larynx. These 2 events prevent passage of food into the trachea. Most essential is the tight approximation of vocal cords, but epiglottis prevents food from ever getting as far as the vocal cords. 4. The upward movement of larynx pulls up and enlarges the opening of the esophagus, i.e. the upper esophageal sphincter, so that food can pass freely into the esophagus. Between swallows it is strongly contracted so that air is prevented from going into oesophagus during respiration

74. 5. At the same time that the larynx is raised and the UES is relaxed, the entire muscular wall of the pharynx contracts , beginning in the superior part of pharynx and spreading downward as a rapid peristaltic wave over the middle and inferior pharyngeal areas , and then into oesophagus. This propels the food into the esophagus . Trachea closed- esophagus opened- fast peristaltic wave originating in pharynx forces bolus into upper esophagus - entire process in less than 2 secs.

75. Pharyngeal stage-Principally a reflex act Almost never initiated by direct stimuli to the swallowing centre from higher regions of CNS. Instead almost always initiated by voluntary movement of food into the back of the mouth, which in turn excites the sensory receptors that elicit the swallowing reflex. Effect on respiration: interrupts respiration for only fraction of the respiratory cycle. Swallowing centre specifically inhibits respiratory centre of the medulla during this time, halting respiration at any point in its cycle to allow swallowing to proceed.

76. Trigger point stimulation starts off at pharyngeal reflexive stage, innervated by CN IX. Stimulation > dialation of pharynx by relaxation of constricters and elevation of pharynx and larynx by contraction of longitudinal muscles Pharynx constricts behind bolus propelling it Contraction of inferior constrictor moves bolus towards esophagus.

77. OESOPHAGEAL STAGE The esophageal stage consists of peristaltic waves The esophagus normally exhibits 2 types of peristaltic movements- primary peristalsis secondary peristalsis

78. PRIMARY PERISTALSIS is a continuation of the peristaltic wave that begins in the pharynx originating from the swallowing centre and coordinated by the vagal nerve This wave takes about 8-10 secs to travel from UES to LES; but liquids travel much faster aided by gravity.

79. SECONDARY PERISTALTIC WAVE Result from distention of esophagus and continue until all the food is emptied into stomach. This wave is coordinated by intrinsic nervous system of esophagus - the myenteric plexus

80. INFANTILE SWALLOW  Normal human fetus can swallow by 12 th week of gestation The infantile swallow is different from the adult swallow. It is a jaws apart swallow. In adults the mandible is stabilized during swallow by clamping of teeth by the muscles of mastication.

81. In infants, the mandible is stabilized by the muscles of facial expression and tongue. The tongue protrudes through the lips and exerts powerful strokes to suckle milk; while the lips form a seal around the nipple. The milk is deposited directly into the posterior aspect of mouth.

82. PHARYNGEAL PHASE : The anatomy of infant’s pharynx allows the laryngeal complex to be elevated so that the epiglottis sits behind the soft palate. The entrance to the larynx is thus elevated and it is placed in the vallecular space just in front of the epiglottis. Thus a functionally continuous tube from nose to larynx to trachea is formed. Normal respiration continues even while feeding. The transition from infantile to adult swallow occurs gradually, usually completed by about 18 months

83. Nervous control Most sensitive tactile areas for deglutition is a ring around the pharyngeal opening, greatest in tonsillar pillars. Mechanoreceptors send signals via glossopharyngeal , trigeminal and vagal nerves to the nucleus of tractus solitarius ( in the medulla ), and then to nucleus ambiguous . These and other interconnected nuclei in the medulla near the IV ventricle comprise the so called ‘ swallowing centre ’ The motor impulses from swallowing centre to muscles and upper esophagus are transmitted by the 5 th ,9 th ,10 th 12 th cranial nerves and some superior cervical nerves

84. NEURAL CONTROL

85. Initiated when food comes in contact with certain trigger areas like fauces, mucosa of posterior pharyngeal wall Via Glossopharyngeal Nerve to brainstem

86. Fourth ventricle in the medulla oblongate of brain Travel through glossopharyngeal & vagus nerves(parasympathetic motor fibers) & reach soft palate ,pharynx & esopahgus Glossopharngeal nerve is concerned with pharyngeal stage of swallowing . Vagus nerve is concerned with esophageal stage

87. Reflex causes upward movement of soft palate to close nasopharynx & upward movement of larynx to close respiratory passage so that bolus enters the esophagus

88. DISORDERS OF MASTICATION & swallowing Most common is chewing inefficiency, due to loss of teeth, particularly posteriors. TMJ disorders can also affect mastication Bruxism:the non-functional grinding or gnashing of teeth & pressing of teeth together in nervous tension or to suppress emotion are called bruxism. Bruxism is caused by occlusal disharmony combined with nervous tension

89. Damage to hypoglossal nerve can affect proper positioning of food on the occlusal table by the tongue. Damage to lingual nerve : the effect of unilateral lingual anesthesia on masticatory efficiency is less, but the tongue becomes very prone to be bitten

90. Abolition of deglutition reflex Results in regurgitation of food into nose or aspiration into larynx. Occurs in paralysis of IXth or Xth cranial nerve Aerophagia Refers to unavoidable swallowing of air along with swallowing of food. Some of the gas is absorbed, some regurgitate into oral cavity(belching), and majority of it passes onto the colon and is expelled as flatus

91. Dysphagia. Difficulty in swallowing due to any cause. Patient usually complains of food getting stuck, a sensation that may be painful. Dysphagia can be the result of lesions of esophagus or pharynx e.g. - cancer or surgery

92. Cardiac achalasia: The LES fails to relax in the absence of oesophageal peristalsis. Emptying of food into stomach is impeded for several hours. The oesophagus can become enlarged and infected.

93. Gastroesophageal reflux disease: GERD is a condition where incompetence of LES causes reflux of acidic gastric contents into oesophagus . It can cause heartburn and may lead to irritation of esophagus and bronchioles.

94. Vomiting, Retching and Gagging Vomiting is a response which is analogous to swallowing but in the opposite direction This is induced by gastric distention or irritation, mechanical stimulation of pharynx, some drugs etc Retching and Gagging refers to unpleasant spasmodic and abortive respiratory movements with the glottis closed Also due to a no. of neuromuscular disorders including stroke, cerebral palsy, multiple sclerosis, Parkinson’s disease and scleroderma

95. CONCLUSION   Mastication includes a vital part of the digestion. It is one of the most important orofacial functions. Chewing doesn’t affect just food, the process of chewing triggers the brain to send preparatory signals to the rest of digestive system such as stomach, gall bladder, pancreas, spleen etc

96. The details of process of deglutition are still controversial. Parts of this complicated act are so rapid that it is impossible to follow with the eye all the movements when observing radiologically the deglutition of radiopaque material & even has not cleared up a number of points.

97. reference Oral Physiology and Bio chemistry - Jenkins Textbook of Physiology - Ganong Oral histology & embryology - Orbans Human Anatomy - Chaurasia Shimizu D, Macho GA, Spears IR. Effect of prism orientation and loading direction on contact stresses in prismatic enamel of primates: implications for interpreting wear patterns. Am J Phys Anthropol . 2005 Apr;126(4):427-34. doi: 10.1002/ajpa.20031. PMID: 15386229.