Mastication & deglutition

Mastication & deglutition

1. MASTICATION & DEGLUTITION

2. Mastication -Definition -Masticatory movements -Role of tongue -Action of muscles -Neural mechanism Swallowing -Definition -Innervation of major muscles -Phases -Neural mechanism Applied Aspects

3. Mastication of food is the initial stage in the process of digestion. Large pieces of food are reduced for swallowing The food is broken apart, and the surface area increased, for the efficient action of digestive enzymes and to facilitate solubilization of food substances in the saliva to stimulate taste receptors. In humans, large vertical movements of the lower jaw. In most species, transverse movements of the mandible, and protrusion and retrusion of the tongue.

4. Masticatory Movements The jaw moves rhythmically, opening and closing in a series of cyclical movements. 4 Phases Minimum opening Jaw moves upward

5. Tongue -Positioning of the food between occlusal surfaces of teeth.

6. Ingestion Swallowing Initial or preparatory period Reducing period Final, preswallowing period

7. Muscles of Mastication Figure 10.7a

8. Muscles of Mastication Figure 10.7b

9. Action of muscles during masticatory movements Opening / Depressor jaw muscles mylohyoid / digastric / lateral pterygoid Closing / elevator jaw muscles medial pterygoid / masseter / tempolaris

10. Closing muscles are usually inactive during jaw opening, when jaw opening muscles are very active. Jaw closing muscles activity -Starts at the beginning of jaw closing -Increases slowly as the teeth begin to interdigitate -More active on the side where food is crushed.

11. Chain Reflex Theory of Mastication In 1917 , C.S. Sherrington Biting on a piece of food in­itiated the jaw-opening reflex; the resulting opening stretched the closer muscles and initiated the jaw-closing response. The alternation of these processes then maintained the rhythmic pat­tern, and produced the movements of mastication.

12. This concept was accepted for many years. W ith the development of electromyographic and neuronal recording techniques, the theory was found to make some false predictions: 1. P aralysis of the muscles should eliminate the masticatory pattern. Dellow and Lund (1971) showed that the rhythmic activity of mas­seter, mylohyoid and hypoglossal nerves persisted after paralysis with gallamine .

13. 2. The rate of masticatory move­ments is much too slow to be explained by chained reflex actions. The chewing rate in animals and humans is in the range of about 0.5 to 5 per second. The latency of the jaw-opening reflex in the cat, from tooth contact to opening, is about 20 ms. That of the jaw-closing reflex, from stretch to closing, is about 10 ms. This implies a total period of the chew­ing cycle of 30 ms , or a masticatory frequency of 33 per second! Since neither cats nor humans use such a rapid form of mastica­tion, it cannot be explained by this mechanism.

14. Central pattern generator/ Masticatory center Interconnected neural circuits form a neural oscillatory network that is capable of generating the pattern of masticatory movements. Other pattern generators responsible for respiration ad swallowing

15. Control Of Mastication -Cyclical movements generated and controlled at the level of brainstem. -Complex interactions between several motor nuclei and sensory input from oral cavity, terminating primarily in the trigeminal sensory and mesencephalic nuclei.

16. Central Pattern Generator Motor nuclei Sensory input terminating in trigeminal nucleus Cortical output neurons Final pattern of mastication is interaction at the brain stem and peripheral sensory input

17. Swallowing is the process of passing food from the mouth into the esophagus where it is transported to the stomach so that the main processes of digestion and nutrient absorption can commence.

18. -Reflex sequence of muscle contractions that propels ingested materials and pooled saliva from mouth to the stomach. Over a period of 24 hours, swallowing occurs as many as 1000 times. -Swallowing frequency i s highest during eating, least during sleep and occurs at a rate of about once per minute at other times.

19. Anatomy of the oral cavity and pharynx in (A) the lateral view and ( B) posterior view

20. The process of swallowing can be divided into four stages : 1 . Preparatory Stage- Merges into terminal phase of mastication 2. Oral Stage- 0.5 s 3. Pharyngeal Stage- 0.7 s 4. Esophageal Stage- Liquids 3 s, Solid 9 s

21. Oral Swallowing Once the bolus is positioned on the dorsum of the tongue, oral phase begins. Lips close, Max and mand incisors come closer together. The ant 2/3 rd of the tongue elevates against the max alveolar ridge and the ant hard palate contracts, propelling the bolus towards the pharynx. Contraction of post pharyngeal wall and side walls of nasopharynx are opposed to seal off the nasopharynx .

22. Pharyngeal Phase The post part of tongue makes rapid piston like movement to propel the bolus through the oropharynx. Movement of the epiglottis closes laryngeal vestibule. Upright Horizontal Rotate caudally over laryngeal vestibule Elevation of hyoid & larynx Further contraction

23. Esophageal Phase - Begins as the bolus passes the upper esophageal splincter . - Peristaltic movements play an important role.

24. It is done by two types of peristaltic contractions : Primary peristalsis Secondary peristalsis Primary peristalsis is a continuation of the peristaltic wave that originates in the pharynx. It extends all the way to the stomach and is sufficiently effective to push the food from the pharynx to the stomach in less than 10 seconds. Secondary peristalsis is the backup motility mechanism of the esophagus. It is triggered by distention of the esophagus due to presence of bolus. Any food that has not passed into the stomach by the primary peristalsia will be pushed by repeated secondary peristaltic waves.

25. Neural control of swallowing Two areas of brain are involved Cerebral cortex Brain stem 28

26. Neural control (initiation) C ertain trigger areas like fauces / mucosa of posterior pharyngeal wall Afferent nerve is the glossopharyngeal nerve Nucleus tractus solitarius & spinal nucleus of trigeminal nerve play a vital role Efferents involve several cranial nerve nuclei which include nucleus ambiguus (muscles of palate, pharynx and larynx), hypoglossal nucleus supplying the muscles of the tongue, motor nuclei of trigeminal and facial nerves supplying the muscles of face, jaws and lips. 29

27. Role of central pattern generator Central pattern generator are a set of neurons capable of initiating sequential swallow Since the process of swallowing and breathing are interlinked there is a certain degree of central co ordination taking place 30

28. Applied Aspects

29. DYSPHAGIA

30. Structural Abnormalities Cleft lip and palate It hampers control for sucking Decreases the oral suction N asal regurgitation.

31. Cervical osteophytes are bony outgrowths from the cervical vertebrae. They may narrow the food path way and direct the bolus toward the airway

32. Zenker diverticulum is a diverticulum of the hypopharynx that occurs at a weak spot in the muscular wall. The bolus can enter in the diverticulum and be regurgitated to the pharynx, which may result in coughing or aspiration.

33. Webs or strictures may occur in the pharynx, esophagus, or sphincters. These can obstruct bolus passage. Stricture is common in the body of the esophagus and is often related to gastroesophageal reflux disease.

34. Achalasia -Esophageal motility is hampered -Failure of relaxation of LES

35. Functional Abnormalities 1.Drooling- reduced closing pressure of the lip 2. Premature leakage of bolus into pharynx- Weak contraction of tongue and soft palate 3. Tongue Dysfunction- Impaired mastication, bolus formation and bolus transport. 4. Loss of teeth 5. Xerostomia 6. Impaired opening of UES- Weakness of ant suprahyoid muscles

36. Aspiration Aspiration is defined as passage of material through the vocal folds. Aspiration of microscopic quantities occurs in normal individuals . Aspiration can occur before, during or after swallowing.

37. Aspiration before the swallow -Entry of liquids into the pharynx -Delayed onset of laryngeal closure after a bolus is propelled into the pharynx Aspiration during the swallow - Hyolaryngeal elevation -Impaired epiglottic tilt -Incomplete closure of the laryngeal vestibule Aspiration after the swallow -Accumulated residue in the pharynx after the swallow.

38. The normal response to aspiration is a strong reflex coughing. Several factors determine the effect of aspiration in a given individual, including the quantity of the aspirate, the depth of the aspiration material in the airway, the physical properties of the aspirate (acidic material is most damaging to the lung, producing chemical pneumonitis. Poor oral hygiene can increase the bacterial load in the aspirate, increasing the risk of bacterial pneumonia

39. References 1.Essentials of Oral Physiology, Robert M Bradley 1 st edition 2.Jones , B., editor. Normal and abnormal swallowing: imaging in diagnosis and therapy. 2nd ed .. Springer- Verlag ; New York: 2003. 3. Dodds WJ, Stewart ET, Logemann JA. Physiology and radiology of the normal oral and pharyngeal phases of swallowing [see comments]. AJR Am J Roentgenol1990;154(5 ):953–963 . [PubMed:2108569 ] 4. Logemann , JA. Evaluation and treatment of swallowing disorders. 2nd ed.. Pro-Ed; Austin Texas: 1998 . 5. Palmer JB, Rudin NJ, Lara G, Crompton AW. Coordination of mastication and swallowing. Dysphagia 1992;7(4 ):187–200. [PubMed: 1308667]

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