Swallowing is a complex and highly coordinated action that most people perform thousands of times daily without conscious thought. This intricate process allows for the safe passage of food and liquids from the mouth to the stomach, preventing them from entering the airway. It is a fundamental function for obtaining nutrition and maintaining overall health.
The Key Muscles for Chewing and Swallowing
Chewing involves powerful muscles that break down food. The masseter and temporalis muscles elevate the jaw to exert significant force for crushing food. The medial and lateral pterygoid muscles assist in jaw opening, clenching, and side-to-side grinding movements. These muscles prepare food for digestion.
The tongue is a flexible muscular organ, composed of intrinsic and extrinsic muscles. It manipulates food, mixing it with saliva to form a bolus. This muscular control also propels the bolus towards the back of the throat, initiating the swallowing sequence.
The soft palate plays a part in this coordinated action. Muscles like the levator veli palatini and tensor veli palatini elevate and tense it. This elevation seals off the nasal cavity during swallowing, preventing food or liquid from entering the nose.
The pharynx contains the pharyngeal constrictors (superior, middle, and inferior). These muscles contract in a sequential, wave-like motion. This action squeezes the food bolus downward, propelling it towards the esophagus.
The Three Phases of the Swallowing Process
The oral phase is the initial, voluntary stage of swallowing. The tongue gathers chewed food and saliva, forming a bolus. The tongue then pushes this bolus against the hard palate and towards the back of the throat. This prepares the bolus for its journey through the pharynx.
The pharyngeal phase is an involuntary, rapid reflex triggered when the bolus reaches the back of the throat. The soft palate elevates to seal off the nasal passage, and the larynx (voice box) rises. This movement, coupled with the folding of the epiglottis over the airway, protects the trachea from food entry. The pharyngeal constrictor muscles then contract in a coordinated wave, squeezing the bolus towards the esophagus.
The esophageal phase is the final, involuntary stage. After passing the upper esophageal sphincter, the bolus enters the esophagus. Here, rhythmic, wave-like muscle contractions, known as peristalsis, propel the food along the esophageal tube. This action moves the bolus towards the stomach, where it passes the lower esophageal sphincter.
Causes of Swallowing Muscle Weakness
Swallowing muscle weakness, or dysphagia, often stems from damage to nerves and muscles. Neurological conditions frequently affect the coordination and strength of these muscles. For example, a stroke can damage the brain regions that send signals to swallowing muscles, leading to impaired control. Conditions like Parkinson’s disease, multiple sclerosis (MS), and amyotrophic lateral sclerosis (ALS) also progressively weaken muscles by affecting nerve pathways or the neuromuscular junction, making swallowing difficult.
Physical damage or obstructions in the throat or esophagus can also compromise swallowing muscle function. Injuries to the head or neck, perhaps from trauma or surgical procedures, may directly damage the muscles or the nerves supplying them. Cancers of the mouth, throat, or esophagus, or their treatments like radiation therapy, can cause scarring or inflammation that restricts muscle movement and coordination.
Age-related changes contribute to swallowing muscle weakness. As individuals age, a natural decline in muscle mass and strength, known as sarcopenia, can affect the muscles of the mouth, pharynx, and esophagus. This atrophy can reduce the force and coordination required for effective swallowing, increasing the risk of difficulties.
Exercises for Swallowing Muscles
Exercises can improve swallowing muscle strength and coordination, though professional guidance is recommended. The Masako Maneuver involves holding the tongue gently between the front teeth while swallowing. This action is designed to strengthen the posterior pharyngeal wall, improving its movement during a swallow. It is important to perform this exercise without food or liquid to prevent choking.
The Mendelsohn Maneuver improves the duration and height of laryngeal elevation during a swallow. Individuals performing this exercise learn to feel their “Adam’s apple” rise and consciously hold it at its highest point for a few seconds before completing the swallow. This sustained elevation helps to keep the airway protected for a longer period and facilitates the opening of the upper esophageal sphincter.
The Shaker Exercise involves lying flat on the back and repeatedly lifting only the head to look at the toes, keeping shoulders flat. This maneuver strengthens the suprahyoid muscles located under the chin. These muscles are responsible for lifting the larynx and opening the upper esophageal sphincter, which helps food pass into the esophagus. Individuals experiencing swallowing difficulties should consult a doctor or a speech-language pathologist before attempting any exercises.