Mastication And Deglutition
Muscles of mastication connect facial bones with the mandible. The facial bones are immobile; and the masticating muscles originate from the facial bones. The contraction of these muscles inserted into the mandible moves the mandible.
Table of Contents
The process of mastication comprises extremely complex but well-coordinated Activities of several group of muscles attached to the mandible.
Read And Learn More: Oral Physiology Notes
Thus mastication includes:
- Mandibular elevation and depression
- Opposing tooth alignment
- Accurate regulation of masticatory forces
Mastication Definition
Mastication (chewing) is a process of mechanical breaking down of food with the help of the teeth and the tongue.
Purpose Of Mastication
- Mastication is the first step in digestion.
- It is needed for mixing the food with the salivary secretion in the mouth (for enzymatic digestion and making of the ground food into bolus for smooth swallowing.
Events In Mastication
Masticatory process and teeth are needed for solid food to be digested. The whole process is a cycle, called masticatory/chewing cycle. This cycle which helps in the breaking down of solid food swallowable bolus has three phases.
- Opening phase: The mouth is opened and the mandible is depressed.
- Closing phase: The mandible is raised towards the maxilla. When the teeth Come in contact with the food, the food is compressed due to the power stroke.
- Occlusal or intercuspal phase: The mandible is stationary and the teeth from both upper and lower arches come close to each other. There is no further vertical movement, but horizontal movements occur.
Mastication (Chewing) Reflex
- Stimulus – food (especially solid food) in the mouth
- Receptor – receptors of sensory neurons
- Afferent nerves – trigeminal nerve
- Centre – swallowing centre (hypothalamus, amygdala and even the cerebral cortex near the sensory areas for taste and smell)
- Efferent nerves – trigeminal nerve
- Effectors – muscles of mastication
Effect is chewing (stretch reflex):
- The presence of food in the mouth at first initiates reflex inhibition of the muscles of mastication, which allows the lower jaw to descend down.
- The decent in turn initiates a stretch reflex ofthe jaw muscles that leads to rebound contraction, raises the jaw to cause closure of the teeth.
- This compresses the bolus against the linings of the mouth, which inhibits the jaw muscles once again.
Muscles Involved In Mastication
The muscles involved in mastication are anatomically and physiologically categorized into two groups.
Primary muscles of mastication are as follows:
- Masseter
- Temporalis
- Lateral pterygoid
- Medial pterygoid
Accessory muscles of mastication are paired muscles
- Digastric
- Mylohyoid
- Geniohyoid
- Stylohyoid
- Buccinator
- Platysma
Primary muscles of mastication are
- Inserted to the mandible
- Concerned with biting and chewing
Primary muscles of mastication:
Mnemonic for primary muscles of mastication:
More Tea Less Milk (Masseter Temporalis Lateral Pterygoid Medial Pterygoid) Or Mom Makes Tasty Latte (Masseter Medial Pterygoid Temporalis Lateral Pterygoid)
Blood Supply And Nerve Supply
- Blood supply is from the maxillary artery, a terminal branch from the external carotid artery.
- Nerve supply is by mandibular division of the trigeminal nerve. Mastication is a voluntary process involving the cerebral cortex and motor neuron areas of the trigeminal nucleus. This process is regulated by a central neural pattern generator, situated in the brain stem (may be in pons, close to the trigeminal motor nucleus and may be either in the medial reticular formation or within the trigeminal main sensory nucleus itself). Neural pattern generators – biological neural networks that produce Rhythmic patterned outputs without sensory feedback.
- The role of the central pattern generator is to send out a series of appropriate signals to the motor neurons involved in directing and coordinating the various muscles of mastication. Further, these basic patterns are modulated by the quality of food (like hardness, size) which can adjust the existing strength and duration of the phases of muscle contraction. Though the central pattern generator takes care of normal mastication, feedback signals from the mouth and descending pathways from the motor cortex can modify the chewing cycles.
Deglutition
Deglutition is a process of swallowing food: The passage of food in the gastrointestinal tract along the pressure gradient.
Phases of deglutition:
There are three phases:
- Buccal/oral phase
- Pharyngeal phase
- Oesophageal phase
1. Buccal/oral phase:
The buccal/oral phase is voluntary
- After mastication, the food is partially digested and mixed With saliva to form the bolus.
- The bolus is voluntarily pushed back towards the pharynx.
- This phase is determined by high pressure in the mouth created by pressing of the bolus against the hard palate.
- The bolus is then pushed towards the pharynx.
2. Pharyngeal phase:
The pharyngeal phase is involuntary.
- As the food is rolled back, the posterior part of the nasopharynx approaches the soft palate resulting in the shutting off of the route of the bolus to the nasopharynx.
Purpose: Prevention of nasal regurgitation of food - In this phase, food is prevented from entering the respiratory tract. When bolus comes in contact with sensory receptors, it initiates the swallowing reflex.
- Larynx elevates, approximation of vocal cords and epiglottis folds form a hood-like covering over the laryngeal opening.
Purpose: Prevent the passage of food into the trachea. - Simultaneously, the upper 3–4 cm of the oesophageal muscular wall, called the upper oesophageal sphincter (also called the pharyngoesophageal sphincter) relaxes, allowing food to move freely from the posterior pharynx into the upper esophagus. There is a temporary cessation of breathing – deglutition apnoea Between swallows, the upper oesophageal sphincter remains powerfully contracted, thereby preventing air from going into the oesophagus during respiration.
3. Oesophageal stage of swallowing
In the oesophagus, the bolus will experience two types of peristaltic movements:
- Primary peristalsis
- Secondary peristalsis
- The contraction of superior constrictor muscles of the pharynx generates the primary peristalsis. The upper oesophageal sphincter relaxes, which allows the passage of food into the esophagus. This wave passes from the pharynx to the stomach in about 8–10 seconds.
- If the primary peristaltic wave fails to empty the esophagus, a secondary Peristaltic wave results due to the distension of the esophagus itself by the retained bolus; these waves are generated proximal to the bolus and continue until all the bolus is emptied into the stomach.
Relaxation of the lower oesophageal sphincter and stomach musculature to receive the bolus is known as receptive relaxation.
Factors Influencing Deglutition
- Consistency of food
- Gravity
- Parasympathetic vagal activity
Deglutition reflex:
- Receptors – situated around the oropharynx
- Afferents – through v, ix, and x cranial nerves
- Centre – located close to the respiratory centres in the floor of the 4th ventricle of the medulla oblongata (nucleus ambiguous and nucleus of tracts solitaries contain the swallowing centers)
- Efferent – ix and xii cranial nerve for the first and second stages, x nerve for the 3rd stage
- Effectors – muscles of the tongue, palate, pharynx, esophagus
Clinical Considerations
Dysphagia: Difficulty in swallowing is called dysphagia.
Causes:
- Oral causes: Sharp tooth injuring the mucosal lining of the mouth, aphthous ulcers
- Pharyngeal causes: Tonsillitis, pharyngitis
- Oesophageal cause: Achalasia cardia, cancer
Mastication And Deglutition Synopsis
- The process of mastication comprises extremely complex but well-coordinated activities of several groups of muscles attached to the mandible.
- It includes, mandibular elevation and depression, opposing tooth alignment, and accurate regulation of masticatory forces.
- Mastication (chewing) is a process of mechanical breaking down of food with the help of the teeth and tongue.
- Masticatory process and teeth are needed for solid food to be digested. The whole process is a cycle, called the masticatory/chewing cycle. This cycle which helps in the breaking down of solid food into swallowable bolus has three phases, i.e. the opening phase, the closing phase, and the occlusal or intercuspal phase.
- The muscles involved in mastication are anatomically and physiologically Categorized into primary muscles of mastication which are the masseter, Temporalis, lateral pterygoid, medial pterygoid.
- Accessory muscles of mastication are paired muscles which include digastric, mylohyoid, geniohyoid, mylohyoid, buccinators, and platysma.
- Mastication is a voluntary process involving the cerebral cortex and motor neuron areas of the trigeminal nucleus.
- Deglutition is a process of swallowing food. The passage of food in the Gastrointestinal tract along the pressure gradient. There are three phases, i.e. Buccal/oral phase, pharyngeal phase and oesophageal phase.
- Consistency of food, gravity and parasympathetic vagal activity influence Deglutition.
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