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The act of swallowing, also known as deglutition, is a complex mechanism involving the coordination of over 30 nerves and muscles. While the initial phase of swallowing is under voluntary control, once the deglutition process starts, it is difficult to stop. The tongue plays a crucial role in initiating the swallow reflex by retracting to direct the bolus, or portion of food, drink, or other material, into the oropharynx. This initial push by the tongue stimulates tactile receptors in the pharynx, triggering the subsequent phases of the swallowing process.
| Characteristics | Values |
|---|---|
| Muscle that initiates swallow | Tongue |
| Type of muscle | Skeletal muscle |
| Tongue blood supply | Lingual artery |
| Hard palate blood supply | Superior alveolar artery, greater palatine artery |
| Soft palate blood supply | Ascending palatine artery |
| Pharyngeal muscles blood supply | External carotid artery, ascending pharyngeal artery |
| Pharyngeal constrictor muscles blood supply | Inferior thyroid artery, tonsillar branch of the facial artery |
| Salpingopharyngeus and palatopharyngeus muscles blood supply | Branch of the facial artery, maxillary artery |
| Number of muscles involved in swallowing | Over 30 |
| Number of cranial nerves involved in swallowing | 5 |
| Swallowing phases | Oral, pharyngeal, esophageal |
| First swallowing phase | Oral phase |
| First swallowing phase type | Voluntary |
| Second and third swallowing phases type | Reflex actions |
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What You'll Learn
The tongue elevates to move food into the oropharynx
The tongue is a skeletal muscle that plays a crucial role in the initiation of swallowing, also known as deglutition. This complex neuromuscular activity involves the coordination of over 30 nerves and muscles, ensuring that food is directed into the digestive tract while also protecting the airway.
During the oral phase of swallowing, the tongue elevates to move food, known as a bolus, into the oropharynx. The tongue retracts and pushes the bolus towards the back of the mouth, making contact with the hard palate for mechanical anchorage. This action generates a pressure wave that propels the bolus into the oropharynx. The oral phase is voluntary and under conscious control, allowing for the necessary actions to form the bolus and prepare it for swallowing.
As the bolus enters the oropharynx, the oral phase is completed, and the pharyngeal phase begins. This phase is reflexive and involuntary, characterised by rapid stimulation and inhibition in the pharyngeal muscles. The pharyngeal muscles contract in a sequential, peristaltic-like manner, creating a cranial-caudal wave of pressure that directs the bolus towards the upper esophageal sphincter (UES). The pharyngeal phase is an irreversible step in the swallowing mechanism, as once initiated, it behaves in an 'all or none' fashion.
During the pharyngeal phase, the tongue maintains its position against the palate, sealing the oropharynx to prevent the bolus from escaping back into the oral cavity. The soft palate elevates, and the uvula rises, closing off the nasopharynx and preventing food from entering the nasal cavity. The larynx and pharynx move down, and the larynx elevates to cover the glottis, protecting the airway. The hyoid bone and larynx move superiorly and anteriorly, positioning the larynx under the base of the tongue to clear the path for the bolus.
The pharyngeal phase ends when the bolus passes through the pharynx and into the esophagus. The upper esophageal sphincter relaxes to allow the bolus to enter, and then it closes to maintain the integrity of the airway. This coordinated response ensures that food is directed into the digestive tract while protecting the airway from aspiration.
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The pharyngeal phase is initiated by touch receptors
The act of swallowing, known as deglutition, is a complex mechanism involving the coordination of over 30 nerves and muscles. It is a critical motor action necessary for calorie intake and survival. The process of swallowing involves three stages: the oral, pharyngeal, and esophageal phases.
The pharyngeal phase is the second stage of the swallowing process and is initiated by touch receptors in the pharynx. This phase begins when a bolus of food is pushed to the back of the mouth by the tongue, or by stimulation of the palate (palatal reflex). The tongue elevates to move the bolus into the oropharynx, where it is held until it aggregates with repeated cycles. Once the bolus reaches the palatoglossal arch of the oropharynx, the pharyngeal phase begins.
Receptors initiating the pharyngeal phase are proprioceptive, and they are scattered over the base of the tongue, the palatoglossal and palatopharyngeal arches, the tonsillar fossa, uvula, and posterior pharyngeal wall. Stimuli from these receptors provoke the pharyngeal phase, which involves a wave of coordinated stimuli lasting about a second. This stage serves two primary purposes: directing food into the oesophagus and protecting the airway from aspiration.
The pharyngeal phase involves the contraction of various muscles to move the bolus through the pharynx and into the oesophagus. The caudal musculature of the pharynx contracts to move the bolus upwards, while the upper oesophageal sphincter relaxes to receive the bolus and then contracts to prevent it from returning to the pharynx. The pharyngeal phase ends when the bolus passes through the sphincter and into the oesophagus.
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The swallowing centre in the brain coordinates the process
The act of swallowing, also known as deglutition, is a complex mechanism that involves the movement of substances from the mouth to the stomach via the pharynx and oesophagus. It is an essential and primitive behaviour that is learned very early in development. The process requires the coordination of over 30 nerves and muscles, including skeletal muscle and smooth muscles.
The second group of neurons is located in the ventrolateral medulla and contains switching neurons, which distribute the swallowing drive to the various pools of motoneurons involved in swallowing. These neurons are part of the ventral swallow group (VSG), located within the RF and just above the nucleus ambiguus (NA). The NA is involved in the swallow motor command. The swallowing reflex is initiated by touch receptors in the pharynx as a bolus of food is pushed to the back of the mouth by the tongue, or by stimulation of the palate (palatal reflex).
The pharyngeal phase, the first irreversible step in the swallowing mechanism, begins when the bolus reaches the palatoglossal arch. Afferent sensory fibres from CN IX, X, and XI in the oropharynx transmit the stimulus to the solitary tract nucleus in the brainstem. Efferent muscle fibres then travel to innervate the muscles of the larynx, pharynx, and oesophagus to coordinate a reflex response. This stage serves two primary purposes: directing food into the oesophagus and protecting the airway from aspiration.
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The airway is protected by the epiglottis
The act of swallowing, also known as deglutition, is a complex mechanism involving the coordination of over 30 nerves and muscles. It is an essential process that directs food from the mouth to the stomach via the pharynx and oesophagus.
The epiglottis is a small, leaf-shaped sheet of elastic cartilage that plays a critical role in protecting the airway during the act of swallowing. When food or liquid is swallowed, the epiglottis reflexively tilts or flips backward, forming a seal over the entrance to the larynx (also known as the voice box or windpipe) and trachea. This movement prevents food or liquid from entering the airway and directs it toward the oesophagus.
The epiglottis is richly supplied with sensory nerve fibres, allowing it to detect the presence of foreign objects and initiate protective reflexes such as swallowing and coughing. This rapid reflexive closure helps safeguard the delicate tissues of the larynx and trachea from damage or irritation. It also prevents aspiration, or the entry of foreign material into the airway, which could lead to serious medical issues such as choking or aspiration pneumonia.
The primary function of the epiglottis is to protect the airway and ensure proper respiratory function. Its role in safeguarding the airway is so significant that disorders or injuries affecting the epiglottis can compromise airway integrity and respiratory health. Conditions such as inflammation, commonly caused by bacterial infections, can lead to swelling and obstruction of the airway, requiring prompt medical attention. Therefore, maintaining the health of the epiglottis through measures such as avoiding smoking and protecting oneself from infections is crucial for respiratory wellbeing.
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The oesophageal phase includes peristalsis
The act of swallowing is a complex mechanism involving the coordination of over 30 nerves and muscles. It can be divided into three phases: oral, pharyngeal, and oesophageal. While the oral phase is entirely voluntary, the pharyngeal and oesophageal phases are mediated by an involuntary reflex called the swallowing reflex. This reflex 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 pharyngeal phase, which precedes the oesophageal phase, involves the movement of the bolus from the oropharynx to the oesophagus. This is achieved through a rapid sequence of contractions by the superior, middle, and inferior pharyngeal constrictor muscles in a top-to-bottom fashion. The pharyngeal phase is also characterised by the relaxation and opening of the upper oesophageal sphincter (UES) to allow the bolus to pass through.
The oral phase, which is entirely voluntary, includes preparatory activities such as suckling, chewing, and masticating, as well as the mixing of food with saliva to form a bolus. The bolus is then pushed to the back of the mouth by the tongue, initiating the swallowing reflex. During the oral phase, the mandible elevates and the lips adduct to assist in containing the food within the oral cavity.
The complex coordination of these three phases ensures the safe and efficient passage of food from the mouth to the stomach during the act of swallowing.
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Frequently asked questions
The tongue initiates the swallow by retracting to direct a bolus of food or drink into the oropharynx.
A bolus is a portion of food, drink, or other materials such as mucus, medications, or secretions that move into the gullet in one swallow.
After the tongue pushes the bolus to the back of the mouth, the pharyngeal phase begins. This phase involves a rapid phase of muscle contraction to propel the bolus through the upper esophageal sphincter and into the esophagus.
