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Questions and Answers
Which anatomical structures are involved in the process of mastication?
Which anatomical structures are involved in the process of mastication?
What role does saliva play during mastication?
What role does saliva play during mastication?
What is the primary function of the chewing reflex?
What is the primary function of the chewing reflex?
Which nerve is primarily responsible for innervating the muscles involved in chewing?
Which nerve is primarily responsible for innervating the muscles involved in chewing?
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What is the stage immediately following the dropping of the lower jaw during chewing?
What is the stage immediately following the dropping of the lower jaw during chewing?
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Which part of the brain is primarily involved in the swallowing reflex?
Which part of the brain is primarily involved in the swallowing reflex?
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Deglutition refers to which of the following processes?
Deglutition refers to which of the following processes?
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Which reflex is NOT typically associated with chewing?
Which reflex is NOT typically associated with chewing?
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What is a potential dietary restriction for edentulous patients?
What is a potential dietary restriction for edentulous patients?
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Which pathway involves efferents from the pharynx and the trigeminal nerve in the swallowing reflex?
Which pathway involves efferents from the pharynx and the trigeminal nerve in the swallowing reflex?
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What is the role of the tensor palatini and levator palatini during the pharyngeal phase?
What is the role of the tensor palatini and levator palatini during the pharyngeal phase?
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During the pharyngeal phase, how long does respiration stop?
During the pharyngeal phase, how long does respiration stop?
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What anatomical feature is formed by the contraction of the superior constrictor muscle?
What anatomical feature is formed by the contraction of the superior constrictor muscle?
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What mechanism primarily coordinates the contractions during the oesophageal phase?
What mechanism primarily coordinates the contractions during the oesophageal phase?
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Which muscle group is responsible for raising and moving the larynx during the swallowing process?
Which muscle group is responsible for raising and moving the larynx during the swallowing process?
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Which structure prevents food from entering the trachea during swallowing?
Which structure prevents food from entering the trachea during swallowing?
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What role does the upper esophageal sphincter (UOS) play in the swallowing process?
What role does the upper esophageal sphincter (UOS) play in the swallowing process?
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Which nerve primarily innervates the body during the oesophageal phase?
Which nerve primarily innervates the body during the oesophageal phase?
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What is the main effect of the approximation of the palatopharyngeal folds during the pharyngeal phase?
What is the main effect of the approximation of the palatopharyngeal folds during the pharyngeal phase?
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What purpose does the closure of the nasopharynx serve during swallowing?
What purpose does the closure of the nasopharynx serve during swallowing?
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Which components form the Dorsal Vagal Complex?
Which components form the Dorsal Vagal Complex?
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What is the primary function of the Dorsal Vagal Complex?
What is the primary function of the Dorsal Vagal Complex?
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Which phase of swallowing involves the voluntary action of squeezing and rolling food?
Which phase of swallowing involves the voluntary action of squeezing and rolling food?
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What is the duration of the pharyngeal phase of swallowing?
What is the duration of the pharyngeal phase of swallowing?
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Which muscle is NOT involved in the swallowing process?
Which muscle is NOT involved in the swallowing process?
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Which part of the gastrointestinal tract is NOT under the control of the Dorsal Vagal Complex?
Which part of the gastrointestinal tract is NOT under the control of the Dorsal Vagal Complex?
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What is the function of the area postrema in the Dorsal Vagal Complex?
What is the function of the area postrema in the Dorsal Vagal Complex?
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Which of the following best describes the oesophageal phase of swallowing?
Which of the following best describes the oesophageal phase of swallowing?
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Which of the following structures is primarily associated with the completion of the voluntary stage of swallowing?
Which of the following structures is primarily associated with the completion of the voluntary stage of swallowing?
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What is the role of the cricothyroid muscle in swallowing?
What is the role of the cricothyroid muscle in swallowing?
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Which of the following mechanisms aids in the opening of the Upper Oesophageal Sphincter (UOS)?
Which of the following mechanisms aids in the opening of the Upper Oesophageal Sphincter (UOS)?
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What initiates the primary peristaltic wave (OPW) in the esophagus?
What initiates the primary peristaltic wave (OPW) in the esophagus?
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What physiological action does the crural portion of the diaphragm perform at the lower esophageal sphincter (LOS)?
What physiological action does the crural portion of the diaphragm perform at the lower esophageal sphincter (LOS)?
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Which of the following factors contributes to the contraction of the lower esophageal sphincter (LOS)?
Which of the following factors contributes to the contraction of the lower esophageal sphincter (LOS)?
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How do enteric inhibitory neurons (EIN) facilitate LOS relaxation?
How do enteric inhibitory neurons (EIN) facilitate LOS relaxation?
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Which condition is associated with defective muscle function affecting swallowing?
Which condition is associated with defective muscle function affecting swallowing?
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What primarily results from the distension of the myenteric plexus after food retention?
What primarily results from the distension of the myenteric plexus after food retention?
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Which of the following accurately describes the role of vagal efferent fibers during swallowing?
Which of the following accurately describes the role of vagal efferent fibers during swallowing?
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What is a common finding associated with tertiary waves in the esophagus?
What is a common finding associated with tertiary waves in the esophagus?
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What factor does NOT contribute to the high resting tone of the lower esophageal sphincter?
What factor does NOT contribute to the high resting tone of the lower esophageal sphincter?
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Study Notes
Chewing
- Mastication is the process of mechanically breaking down food.
- Involves action of teeth: incisors for cutting, molars for grinding.
- Jaw muscles are regulated by higher brain centers.
- Individuals without teeth (edentulous) require a soft diet.
Functions of Mastication
- Aids digestion by increasing surface area for enzyme action.
- Mixes food with saliva and lubricates it for easier swallowing.
- Prevents damage (excoriation) to the gut wall.
- Facilitates food emptying and movement through the digestive tract.
Regulation of Chewing
- Controlled by nuclei located in the brainstem, cerebral cortex, hypothalamus, and amygdala.
- Motor branch of the trigeminal nerve (cranial nerve V) innervates the muscles of chewing.
Chewing Reflex
- Initiated by the presence of food in the mouth.
- This triggers a reflex inhibition of mastication muscles, causing the jaw to drop.
- The jaw muscles stretch, resulting in a rebound contraction that raises the jaw.
- The teeth close, compressing food against the mouth lining.
- Further reflex inhibition of the mastication muscles occurs, restarting the cycle.
Deglutition (Swallowing)
- A reflex action moving air, liquids, and solids from the mouth to the stomach.
Regulatory Pathways for Swallowing
- Controlled by the swallowing center in the brainstem reticular formation.
- Involves the nucleus ambiguus, tractus solitarius, and dorsal motor nucleus of the vagus nerve.
- Afferent (sensory) nerves from the pharynx and cranial nerves V, VII, and XII carry information about the bolus.
- Efferent (motor) nerves, including V, VII, IX, X, and the hypoglossal nerve, control muscle action during swallowing.
Vagal Integrative Center for the Upper GI Tract
- Includes the dorsal motor nucleus of the vagus, nuclei of ambiguus, tractus solitarius, and area postrema.
- Known as the dorsal vagal complex, located in the medulla oblongata.
- Responsible for integrating vagal control of the esophagus, stomach, duodenum, pancreas, and gallbladder.
Muscles Involved in Swallowing
- Oral/Facial muscles: Masseter, temporalis, pterygoideus (lateral & medial), tensor palatini, digastricus, stylohyoideus, facial muscles.
- Pharyngeal Muscles: Palatopharyngeus, palatoglossus, levator palatini, salpingopharyngeus, superior, middle & inferior constrictors.
- Laryngeal Muscles: Cricothyroideus, cricoarytenoideus, interarytenoideus.
- Tongue Muscles: Geniohyoideus, thyrohyoideus (extrinsic) - posterior intrinsic tongue muscles, hypoglossus, genioglossus, styloglossus.
- Esophageal Muscles: Esophageal muscles (smooth & striated)
Swallowing Stages
- Voluntary: Food is moved posteriorly by the tongue and pressed against the hard palate, then soft palate into the oropharynx.
-
Involuntary:
- Pharyngeal Phase (< 1 second): Closure of the nasopharynx, respiration inhibited, bolus propelled through the pharynx by pharyngeal peristalsis.
- Esophageal Phase (8-10 seconds): Bolus moves from pharynx to stomach via peristalsis.
Pharyngeal Phase
- Nasopharynx closure accomplished by contraction of the tensor palatini and levator palatini muscles, elevating the soft palate.
- Superior constrictor muscle contraction forms the ridge of Passavant, creating a seal and initiating pharyngeal peristalsis.
- Palatopharyngeal folds approximate to form a slit, allowing for passage of properly masticated food.
- Larynx closure: hyoid bone is raised & moved forward by geniohyoid & mylohyoid muscles, bringing the larynx under the tongue.
- Vocal cords approximate.
- Epiglottis swings backward over the larynx opening to prevent food entry.
Esophageal Phase
- UOS (upper esophageal sphincter) closure at the top of the esophagus.
- Cricopharyngeal, or pharyngoesophageal, sphincter is a striated muscle.
- A primary peristaltic wave (OPW) is initiated in the pharynx and propels the bolus distally at 4 cm/sec over 8-10 seconds.
- Gravity assists bolus movement.
- Secondary OPW is triggered by retained food distending the myenteric plexus.
- Tertiary waves can indicate pathology.
Lower Esophageal Sphincter (LOS)
- A physiological sphincter created by:
- Smooth muscle thickening at the stomach junction.
- Crural portion of the diaphragm surrounding the esophagus.
- Oblique stomach fibers form a flap valve.
- LOS closes during high intragastric pressure to prevent reflux.
LOS Function
- High resting tone of the UOS and LOS act as a barrier against air and gastric contents.
- The esophageal body is flaccid at rest.
- Sequential body contractions propel the bolus distally.
- Contractions are coordinated centrally and peripherally.
LOS Contraction and Relaxation
- Contraction is induced by myogenic, neural (acetylcholine), and humoral factors.
- Smooth muscle contracts when stretched.
- Relaxation is neurally mediated by vagal efferent fibers stimulating enteric inhibitory neurons (EIN).
- EIN release vasoactive intestinal peptide (VIP) and nitric oxide (NO) to relax smooth muscle.
Esophageal Coordination and Receptive Relaxation
- Vagus nerve coordinates esophageal contractions with somatic and visceral motor nerves.
- Vago-vagal reflexes are triggered by esophageal body stretching.
- Receptive relaxation of the stomach allows the bolus to enter and complete swallowing.
Disorders of Chewing & Swallowing
- Sphincter disorders: Achalasia (LES failure to relax), Incompetent LOS ("heartburn").
- Nerve Damage: Cranial nerves V, IX, X affected by conditions like poliomyelitis or encephalitis.
- Muscle dysfunction: Myasthenia gravis, muscle dystrophy, diffuse esophageal spasm.
- Glottis remains open: Drug-induced.
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Description
Test your knowledge on the process of mastication, its functions, and regulation in relation to the digestive system. This quiz covers the mechanics involved in chewing, the role of different teeth, and the neurological control of jaw movement.