Figure 2.

A summary of oropharyngeal structures, cranial nerves, and neural circuits necessary for normal feeding and swallowing. A. The key oropharyngeal skeletal (gray/white), muscular (pink) and other soft tissue (dark pink) structures necessary for feeding and swallowing around birth (left) and in adulthood (right). Note that the soft palate (velum; stipple) must be elevated and the epiglottis must be lowered to prevent aspiration into the nasopharynx and trachea, respectively. The relationship between these structures, the mouth and the esophagus (blue) changes between birth and adulthood (after [33]). B. Multiple cranial nerves are essential for optimal feeding and swallowing. These nerves are clearly defined in the embryo (left) and in the adult (right). Cranial Nerve (CN) V (trigeminal) provides much of the innervation for the lips, tongue and palate. CN VII (facial) innervates primarily the tongue. CN IX (glossopharyngeal) innervates primarily the tongue and pharynx/esophagus, and CN X innervates the larynx and the pharynx. Finally, CN XII innervates the muscles of the tongue. C. The basic organization of the neural circuit for feeding and swallowing reflects sensory input from peripheral cranial sensory ganglia whose axons run in the cranial nerves summarized in panel B, as well as cranial motor neurons in the brainstem whose activity is modulated by multiple inhibitory interneurons, and whose axons also travel to peripheral muscles via the cranial nerves summarized in panel B.