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The act of swallowing, also known as deglutition, is a complex mechanism involving the coordination of over 20 muscles and more than 30 nerves. The tongue is the primary muscle that initiates the swallowing process, with the tongue tip making contact with the hard palate for mechanical anchorage. The tongue then contracts to push the bolus of food or liquid to the back of the mouth, triggering the pharyngeal phase, which is a rapid sequence of muscle contractions that propel the bolus through the upper oesophageal sphincter and into the oesophagus.
| Characteristics | Values |
|---|---|
| Number of muscles involved | Over 20 |
| Muscle groups involved | Oral cavity, pharynx, larynx, and oesophagus |
| Muscle types involved | Skeletal, smooth |
| Muscle functions | Contraction, relaxation, elevation, tilting, blocking, sealing, dilation, constriction, propulsion |
| Muscle blood supply | External carotid artery, superior alveolar artery, ascending palatine artery, maxillary artery, ascending pharyngeal artery, inferior thyroid artery, facial artery |
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What You'll Learn
The tongue pushes the bolus to the back of the throat
The tongue plays a crucial role in the complex process of swallowing, which involves the coordination of dozens of muscles and nerves in the oral cavity, pharynx, larynx, and oesophagus. This mechanism, known as deglutition, propels food from the mouth to the stomach while also protecting the airway.
During the oral phase of swallowing, the tongue elevates and pushes the bolus of food posteriorly into the oropharynx, located at the back of the throat. This action is facilitated by the depression and retraction of the tongue, which increases the size of the oral cavity to accommodate the ingested bolus. The tongue also seals the bolus within the oral cavity, preventing its escape back into the mouth. Specifically, the posterior tongue rises to meet the soft palate, forming a seal that is particularly important when swallowing liquids.
As the tongue pushes the bolus towards the oropharynx, the oral phase of swallowing concludes, and the pharyngeal phase begins. This phase involves the rapid contraction of muscles to propel the bolus through the upper oesophageal sphincter and into the oesophagus. The tongue's role in this stage is to maintain the seal against the soft palate, preventing retrograde escape.
The forceful action of the tongue in pushing the bolus to the back of the throat is a vital step in the swallowing process. It sets the stage for the subsequent phases, ensuring that food is directed towards the oesophagus and protecting the airway from aspiration. The tongue's ability to elevate and seal the bolus demonstrates its essential function in coordinating the complex movements required for successful deglutition.
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The pharyngeal phase is initiated
The pharyngeal phase is the second stage of the swallowing process, which is a complex, multifaceted process involving a variety of muscles and nerves. It is an essential behaviour that humans learn very early in development. The pharyngeal phase is initiated when the bolus reaches the palatoglossal arch, which is the first irreversible step in the swallowing mechanism. This step is characterised by a wave of coordinated stimuli lasting about a second, ending as the food bolus reaches the upper oesophageal sphincter (UES).
The pharyngeal phase is a reflex action that occurs when afferent sensory fibres from CN IX, X, and XI in the oropharynx transmit the stimulus to the solitary tract nucleus in the brainstem. This stimulus triggers the contraction of the thyrohyoid, moving the larynx and hyoid superiorly and anteriorly, thereby initiating the opening of the sphincter. This is followed by the manometric relaxation of the cricopharyngeus and pressure-dependent distension of the UES by the bolus. The pharyngeal phase also serves to protect the airway from aspiration.
During the pharyngeal stage, the soft palate is elevated by the tensor palatini and levator palatini to seal the nasopharynx and prevent pressure escape into the nasal cavity. This phase involves the contraction of pharyngeal constrictor muscles, which receive blood from the inferior thyroid artery and the tonsillar branch of the facial artery. The pharyngeal phase is a rapid process, ensuring that the bolus is propelled through the upper oesophageal sphincter and into the oesophagus.
The pharyngeal phase is a critical step in the swallowing mechanism, ensuring that food is directed into the oesophagus while also protecting the airway. This phase involves the coordination of multiple muscles and nerves to facilitate the passage of food and prevent aspiration.
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The airway is protected
The act of swallowing, also known as deglutition, is a complex mechanism involving the coordination of over 20 muscles and more than 30 nerves. It is a protective mechanism for the airway, preventing food from entering the trachea.
The pharyngeal phase of swallowing is the first irreversible step in the swallowing mechanism. During this phase, the airway is protected by the induction of a swallowing apnea, a cessation in breathing that prevents the aspiration of consumed material. The airway is physically closed by the elevation of the soft palate and tilting of the epiglottis, which acts as a trapdoor to close off the upper airway. The epiglottis is controlled by a complex reflex that facilitates the elevation of the hyoid bone and thyroid cartilage.
The pharyngeal phase is initiated by touch receptors in the pharynx as a bolus of food is pushed to the back of the mouth by the tongue. The tongue is supplied with blood by the lingual artery, a branch of the external carotid. The tongue elevates to move the bolus into the oropharynx, where it is held until it aggregates with repeated cycles. The pharyngeal phase is an involuntary process, characterised by a rapid phase of muscle contraction to propel the bolus through the upper oesophageal sphincter and into the oesophagus.
The oesophageal phase includes the following activities: food passes through the upper oesophageal sphincter to the oesophagus, a peristaltic wave develops, and the lower oesophageal sphincter relaxes to allow the bolus to enter the stomach. The oesophageal phase is also an involuntary process, involving the contraction and relaxation of smooth muscles surrounding the digestive tract.
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The oesophageal phase begins
The act of swallowing is a complex process that involves the coordination of over 20 muscles and 30 nerves. It is divided into three stages: the oral phase, the pharyngeal phase, and the oesophageal phase. The oral phase is voluntary, while the pharyngeal and oesophageal phases are involuntary and mediated by a reflex called the swallowing reflex.
The primary mechanism of airway protection during the oesophageal phase is the closure of the vocal folds and the glottis. The vocal folds adduct, and the glottis closes to prevent the leakage of food or liquid into the airway. This stage also involves the elevation of the soft palate via the tensor palatini and levator palatini muscles, which seal the nasopharynx to prevent pressure escape into the nasal cavity.
The oesophageal phase is a rapid process, with a travel time through the oesophagus of approximately 5 to 6 seconds, and a velocity of peristalsis at 3 to 4 cm/sec. This phase involves the coordination of several muscles, including the pharyngeal constrictor muscles, which receive blood from the inferior thyroid artery and the tonsillar branch of the facial artery. The salpingopharyngeus and palatopharyngeus muscles are also involved and receive blood supply from a branch of the facial artery and maxillary artery.
The oesophageal phase is an essential part of the swallowing mechanism, ensuring that food is safely transported from the oral cavity to the stomach. It is a complex and highly coordinated process that involves the precise activation and control of various muscles and nerves.
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Swallowing is a complex mechanism
Swallowing, also known as deglutition, is a complex mechanism involving the coordination of over 20 muscles and more than 30 nerves. It is an essential function that develops early in fetal life, around the beginning of the fourth week of embryological development. The pharyngeal arches begin to form during this time, eventually giving rise to the mature adult structures used in swallowing.
The process of swallowing involves the movement of substances from the mouth (oral cavity) to the stomach via the pharynx and oesophagus. It is divided into three stages: the oral phase, pharyngeal phase, and oesophageal phase. The oral phase is voluntary, while the pharyngeal and oesophageal phases are reflex actions. During the oral phase, food or liquid enters the oral cavity, and the mandible elevates and the lips adduct to contain it. The tongue then pushes the food or liquid to the back of the throat, where it forms a bolus with the help of saliva.
The pharyngeal phase begins when the bolus reaches the palatoglossal arch of the oropharynx. This phase is involuntary and involves a rapid contraction of muscles to propel the bolus through the upper oesophageal sphincter and into the oesophagus. The pharyngeal stage serves to protect the airway from aspiration. During this stage, the airway is physically closed by the elevation of the soft palate and tilting of the epiglottis, which prevents food or liquid from entering the trachea.
The oesophageal phase involves the passage of the bolus through the oesophagus and into the stomach. This is accomplished through peristalsis, or alternating contractions and relaxations of the smooth muscles surrounding the digestive tract. The lower oesophageal sphincter relaxes to allow the bolus to enter the stomach, but it remains contracted at rest to prevent regurgitation.
The complex mechanism of swallowing is controlled by several cortical areas and the swallowing centres in the brain stem. The brain communicates with the muscles through cranial nerves, and the process is coordinated by the autonomic nervous system. While most individuals give little thought to swallowing, it can be a significant area of concern for those with conditions such as strokes, Alzheimer's disease, or cerebral palsy, which can interfere with the neuromuscular structures and coordination involved in swallowing.
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Frequently asked questions
The tongue is the first muscle involved in swallowing.
The oral phase is the first stage of swallowing.
The pharyngeal stage is the first irreversible step in the swallowing mechanism.
The tongue pushes the bolus to the back of the throat.
Swallowing serves as a vital protector of the airway and directs food into the digestive tract.
