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Swallowing is a complex mechanism using both skeletal muscle and smooth muscles of the pharynx and esophagus. The autonomic nervous system (ANS) coordinates this process in the pharyngeal and esophageal phases. Real-time MRI – swallowing Sagittal view of mouth and pharynx
Stylopharyngeus muscle; Salpingopharyngeus muscle; Palatopharyngeus muscle; During swallowing, these muscles act to shorten and widen the pharynx. They are innervated by the pharyngeal branch of the vagus nerve (CN X) with the exception of the stylopharyngeus muscle which is innervated by the glossopharyngeal nerve (CN IX). [1]
The soft palate is moveable, consisting of muscle fibers sheathed in mucous membrane. It is responsible for closing off the nasal passages during the act of swallowing, and also for closing off the airway. During sneezing, it protects the nasal passage by diverting a portion of the excreted substance to the mouth.
The muscle contracts during swallowing: [1] as soon as the bolus of food is received in the pharynx, the elevator muscles relax, the pharynx descends, and the constrictors contract upon the bolus, and convey it downward towards the esophagus. [2] [3] They also have respiratory mechanical effects. [4]
These four muscles have different actions, but in general assist in elevating the hyoid bone and widening the esophagus during swallowing.When the two bellies of the digastric contract, they pull upward on the hyoid bone; but if the hyoid is fixed from below, the digastric assists in extreme opening of the mouth such as yawning or taking a large bite of an apple. [1]
Carnivores generally chew very little or swallow their food whole or in chunks. [11] This act of gulping food (or medicine pills) without chewing has inspired the English idiom "wolfing it down". [12] Other animals such as cows chew their food for long periods to allow for proper digestion in a process known as rumination.
The muscles supplied by the vagus (included with this is the cranial root of the accessory nerve), such as levator veli palatini, are also necessary to swallow properly through integration by the nucleus of the solitary tract. The vagus also supplies the upper part of the esophagus, and other parts of the pharynx and larynx.
The levator veli palatini (/ l ɪ ˈ v eɪ t ər ˈ v iː l aɪ ˌ p æ l ə ˈ t aɪ n aɪ /) is a muscle of the soft palate and pharynx. It is innervated by the vagus nerve (cranial nerve X) via its pharyngeal plexus. During swallowing, it contracts, elevating the soft palate to help prevent food from entering the nasopharynx.