Physiology of Mastication and Deglutition

Mastication

the act of chewing food, and it consists of the coordinated function of various part of the oral cavity to prepare the food for swallowing and digestion

Mastication (definition)

the cyclic movement produced by the elevation and depression of the mandible as food is sheared and formed into a bolus in preparation for swallowing

Mastication of food

the initial stage in the process of digestion

Mastication function

large pieces of food are reduced for swallowing

Mastication function

food is broken apart and the surface area increased for efficient action of digestive enzymes and to facilitate solubilisation of food substances in saliva to stimulate taste receptors

Teeth

most important structure involved in mastication that crushes food by grinding action making it suitable for swallowing and increasing surface area

Tongue

maneuvering the food within the oral cavity

Tongue function

initiates the breaking of food

Tongue function

pushes food to occlusal surfaces of teeth during opening phase and repositions the crushed food

Tongue function

divides food into portions that require more chewing and portions that are to be swallowed

Tongue function

sweeps the teeth to remove food residue trapped in the oral cavity

Lips and cheeks

help hold food in the mouth and keep it in place for chewing

Lips

guide, control intake, and seal off the oral cavity

Periodontium

structural and functional group of tissues that facilitate anchorage of teeth in jaws and provide resilient attachment during mastication

Chewing reflex

presence of bolus causes reflex inhibition of muscles of mastication causing lower jaw to drop, followed by stretch reflex leading to rebound contraction and closure of teeth compressing the bolus, repeating cyclically

Chewing cycle

repetitive sequence of jaw opening and closing with a profile in the vertical plane

Opening phase

the mouth is opened and the mandible is depressed

Closing phase

the mandible is raised towards the maxilla

Occlusal phase

the mandible is stationary and the teeth from both upper and lower arches approximate

Muscles of mastication (closing)

masseter, medial pterygoid, temporalis

Muscles of mastication (opening)

depressor muscles, lateral pterygoid, digastric, mylohyoid and geniohyoid

Muscles of mastication (protrusion)

medial pterygoid, lateral pterygoid, masseter

Muscles of mastication (retraction)

temporalis

Muscles of mastication (side to side movement)

medial pterygoid, lateral pterygoid

Control of mastication

movement requires integrated activity of muscles controlled by trigeminal, hypoglossal, facial and other motor nuclei in the brainstem with sensory input from the oral cavity

Deglutition

reflex activity consisting of muscle contractions and relaxations that push ingested food and saliva from the mouth to the stomach

Swallowing reflex

pre-programmed and initiated in the brainstem swallowing center

Oral cavity structures

tongue, hyoglossus, genioglossus, styloglossus (CN XII), palatoglossus, mylohyoid (CN V3), mastication muscles

Mastication muscles

masseter, temporalis, lateral and medial pterygoid (CN V3)

Pharynx muscles

tensor palatini (CN V3), levator palatini (CN IX, X), suprahyoid muscles, infrahyoid muscles

Suprahyoid muscles

digastric (CN V3 & VII), stylohyoid (CN VII), geniohyoid (CN XII), mylohyoid (CN V3)

Infrahyoid muscles

sternohyoid, sternothyroid (ansa cervicalis), thyrohyoid (CN XII), omohyoid (ansa cervicalis)

Longitudinal pharyngeal muscles

stylopharyngeus (CN IX), salpingopharyngeus (CN X), palatopharyngeus (CN X)

Pharyngeal constrictor muscles

superior, middle, and inferior (CN X)

Cricopharyngeus muscle

controlled by recurrent laryngeal nerve

Larynx muscles

posterior cricoarytenoid, lateral cricoarytenoids, oblique and transverse arytenoids, aryepiglotticus

Phases of swallowing

preparatory, oral, pharyngeal and esophageal phases

Preparatory phase

formation of food bolus in the mouth after chewing as a preparatory event for swallowing

Food bolus

round or oval shaped mass of food formed in the mouth

Oral phase

begins when bolus is on tongue dorsum, lips close, incisors come together, tongue elevates and propels bolus toward pharynx, soft palate moves upward to shut nasopharynx, voluntary phase with temporary توقف of respiration

Pharyngeal phase

posterior tongue propels bolus, pharyngeal constrictors contract sequentially, upper esophageal sphincter opens, epiglottis closes laryngeal vestibule

Esophageal phase

upper esophageal sphincter contracts and peristaltic movements push bolus to stomach, lower esophageal sphincter opens

Phase one (oral phase)

collection and swallowing of masticated food

Phase two (pharyngeal phase)

passage of food through pharynx into beginning of esophagus

Phase three (esophageal phase)

passage of food into the stomach

Control of swallowing

oral phase is voluntary

Control of swallowing

pharyngeal and esophageal phases are involuntary

Somatic (adult) swallow

uses the teeth to stabilize the mandible

Visceral (infantile) swallow

mandible is stabilized by tongue pushing forwards between the arches and against the anterior palate

TMJ disorders

disorders associated with mastication and swallowing

Achalasia

esophageal motility disorder involving smooth muscle layer and lower esophageal sphincter with failure of relaxation

Gastroesophageal reflux disease

disorder associated with swallowing

Parotitis

inflammation of one or both parotid glands

Dysphagia

difficulty or discomfort in swallowing

Zenker diverticulum

diverticulum of hypopharynx where bolus can enter and be regurgitated causing coughing or aspiration