- Preparatory Phase
Mastication involves breaking down food particles and mixing
them with saliva. The teeth crush the food during chewing as a variety of movements occur at the temporomandibular joint (TMJ). The forces that move the mandible during chewing are the muscles of mastication.
(figure adapted from Logemann, 1983)
Throughout mastication, food particles fall within the oral cavity and into the lateral sulcii. The tongue pushes the particles that fall medially back to the top of the teeth from whence they came or carries the particles to the teeth on the other side for further crushing. Lower facial muscles, such as the buccinator, act to squeeze the food particles that fall laterally back to the tops of the teeth. The action of muscles like the orbicularis oris, which helps seal the lips, prevent food from falling outside the mouth.
Oral Phase
The tongue forms food particles into a bolus by cupping.
The tongue's middle portion depresses while its anterior, posterior, and lateral portions elevate against the hard palate (roof of the mouth.) The tongue's cupping forms a central groove which contains the bolus. Elevation of the tongue's anterior portion causes the bolus to flow posteriorly. However, the bolus does not yet enter the pharnyx because the posterior part of the tongue elevates against the soft palate (velum).
Pharyngeal Phase
Pressure of the bolus against the anterior faucial arches
triggers the swallow reflex. Activation of sensory receptors in the fauces produces afferent activity in various cranial nerves. This sensory activity results in reflex motor activity that initiates the swallow (Kendall, McCreary, & Provance, 1993, p.320). The soft palate retracts and elevates to protect the nasal cavity. Pharyngeal peristalsis carries the bolus through the pharynx to the top of the esophagus at the cricopharyngeal sphincter. The cricopharyngeal sphincter relaxes, allowing the bolus to pass into the esophagus.
To protect the trachea's opening and prevent food from entering the lungs' sterile environment and causing "aspiration pneumonia," the aryepiglottic folds, false vocal folds, and true vocal cords all close. Airway closure also occurs because of activity in the hyoid muscles. Suprahyoid muscles elevate the hyoid bone. Infrahyoid muscles connect, in turn, to the thyroid and cricoid cartilage. Elevation of these structures permits the epiglottis to lay over the trachea's opening, protecting the airway.
- Esophageal Phase
A peristaltic wave of muscle action pushes food through the esophagus into the stomach.
If a swallow is not actively triggered during the pharyngeal phase, the risk of aspiration, food entering the airway, increases. Aspiration can lead to pneumonia. A strong cough can expel food by quickly decreasing intrathoracic volume and increasing pressure in the airway.
Mastication involves breaking down food particles and mixing
them with saliva. The teeth crush the food during chewing as a variety of movements occur at the temporomandibular joint (TMJ). The forces that move the mandible during chewing are the muscles of mastication.
(figure adapted from Logemann, 1983) |
|---|
Throughout mastication, food particles fall within the oral cavity and into the lateral sulcii. The tongue pushes the particles that fall medially back to the top of the teeth from whence they came or carries the particles to the teeth on the other side for further crushing. Lower facial muscles, such as the buccinator, act to squeeze the food particles that fall laterally back to the tops of the teeth. The action of muscles like the orbicularis oris, which helps seal the lips, prevent food from falling outside the mouth.
Oral Phase
The tongue forms food particles into a bolus by cupping.
The tongue's middle portion depresses while its anterior, posterior, and lateral portions elevate against the hard palate (roof of the mouth.) The tongue's cupping forms a central groove which contains the bolus. Elevation of the tongue's anterior portion causes the bolus to flow posteriorly. However, the bolus does not yet enter the pharnyx because the posterior part of the tongue elevates against the soft palate (velum).
Pharyngeal Phase
Pressure of the bolus against the anterior faucial arches
triggers the swallow reflex. Activation of sensory receptors in the fauces produces afferent activity in various cranial nerves. This sensory activity results in reflex motor activity that initiates the swallow (Kendall, McCreary, & Provance, 1993, p.320). The soft palate retracts and elevates to protect the nasal cavity. Pharyngeal peristalsis carries the bolus through the pharynx to the top of the esophagus at the cricopharyngeal sphincter. The cricopharyngeal sphincter relaxes, allowing the bolus to pass into the esophagus.
To protect the trachea's opening and prevent food from entering the lungs' sterile environment and causing "aspiration pneumonia," the aryepiglottic folds, false vocal folds, and true vocal cords all close. Airway closure also occurs because of activity in the hyoid muscles. Suprahyoid muscles elevate the hyoid bone. Infrahyoid muscles connect, in turn, to the thyroid and cricoid cartilage. Elevation of these structures permits the epiglottis to lay over the trachea's opening, protecting the airway.