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Swallowing is a complex process that involves coordination between multiple structures and muscles in the head, neck, and throat. The control of swallowing is orchestrated by the swallowing center, which is located in the brainstem. Here’s an overview of how swallowing is controlled:

Initiation of Swallowing: Swallowing is triggered by sensory input from the mouth and throat, such as the presence of food or liquid. These sensory signals are detected by receptors in the oral cavity and transmitted to the swallowing center in the brainstem. 

Swallowing Reflex: Upon receiving sensory input, the swallowing center initiates the swallowing reflex. This reflex involves a series of coordinated muscle contractions and relaxations to move the food or liquid through the different stages of swallowing. 

Oral Phase: The oral phase of swallowing begins with the voluntary process of chewing and manipulating food in the mouth. The tongue pushes the food to the back of the mouth, triggering the swallowing reflex. The muscles of the soft palate and tongue then seal off the nasal cavity to prevent food or liquid from entering. 

Pharyngeal Phase: The pharyngeal phase starts when the food or liquid reaches the back of the throat (pharynx). The swallowing reflex triggers a series of rapid muscle contractions in the pharyngeal walls, elevating the larynx (voice box) and closing the entrance to the trachea (windpipe) to prevent aspiration. The epiglottis, a flap-like structure, covers the entrance to the trachea, directing the food or liquid into the esophagus. 

Esophageal Phase: After passing through the pharynx, the food or liquid enters the esophagus, a muscular tube that connects the throat to the stomach. Peristaltic contractions of the esophageal muscles propel the bolus (food or liquid) downward towards the stomach.

The hypoglossal nucleus and nucleus ambiguus are two important structures in the brainstem that play specific roles in controlling swallowing. The hypoglossal nucleus is located in the medulla oblongata, specifically in the lower part of the brainstem. It is responsible for controlling the movements of the muscles in the tongue (intrinsic and extrinsic tongue muscles). During swallowing, the hypoglossal nucleus sends signals to these muscles, coordinating their contractions and movements to facilitate the proper positioning and manipulation of the food bolus in the oral phase of swallowing. Dysfunction of the hypoglossal nucleus can lead to difficulties in tongue movement and can affect swallowing function. Furthermore, nucleus ambiguus is another brainstem structure located in the medulla oblongata, adjacent to the hypoglossal nucleus. It plays a crucial role in controlling the muscles involved in the pharyngeal and laryngeal phases of swallowing. The nucleus ambiguus sends motor signals to the muscles of the soft palate, pharynx, and larynx, coordinating their contractions and relaxations during swallowing. This helps to ensure the proper closure of the airway, elevation of the larynx, and protection against aspiration of food or liquid into the trachea. Dysfunction or damage to these nuclei can disrupt the precise control of the relevant muscles, leading to difficulties in swallowing, aspiration, or other swallowing-related issues.