The pharynx is the superior expanded part of the alimentary system. It links the oral cavity and the nasal cavities in the head with the larynx and esophagus in the neck. It is a common pathway for food and air. The pharynx extends from the base of the skull to the inferior border of the cricoid cartilage anteriorly and the inferior border of the sixth cervical vertebra (C6) posteriorly.
The pharynx is widest opposite to the hyoid bone, and narrowest at its inferior end that is continuous with the esophagus. Its posterior wall lies against the prevertebral layer of the deep cervical fascia, while its anterior wall attaches to the margins of the nasal cavities, oral cavities, and the larynx. Based on that, the pharynx is subdivided into three parts: the nasopharynx, oropharynx, and the laryngopharynx.
The nasopharynx is located behind the posterior apertures of the nasal cavities, superior to the level of the soft palate. It has a respiratory function.
The oropharynx lies posterior to the oral cavity, inferior to the level of the soft palate and superior to the epiglottis. It has a digestive function.
The laryngopharynx lies posterior to the larynx, extending from the superior margin of the epiglottis to the inferior border of the cricoid cartilage, where it narrows and becomes continuous with the esophagus. It is where both food and air pass.
The pharynx skeletal framework consists of bones, cartilages and ligaments. The pharyngeal muscles are organized into two groups: constrictor and longitudinal muscles.
The constrictor muscles have fibers oriented in a circular direction and they are three in number on each side. These muscles are the superior, inferior and middle constrictor muscles named according to their position. The constrictor muscles are joined posteriorly by the pharyngeal raphe ligament, while anteriorly they attach to the bones and ligaments on the lateral margins of the nasal and oral cavities and the larynx. The constrictor muscles overlap each other in position, and collectively they constrict and narrow the pharyngeal cavity. When these muscles contract sequentially from the top to the bottom (swallowing), the food bolus moves from the pharynx into the esophagus.
The longitudinal muscles, on the other hand, are vertically oriented and are named according to their origin. Those muscles are also three in number. They are the stylopharyngeus, salpingopharyngeus and the palatopharyngeus muscles. From their site of origin, those muscles descend and attach to the pharyngeal wall, where they elevate it during swallowing, as the food bolus moves through the pharynx.
The vasculature of the pharynx is supplied by numerous vessels. Those that supply its upper portion are the ascending pharyngeal artery, the ascending palatine and tonsillar branches of the facial artery, and several branches from the maxillary and lingual arteries. All those blood vessels originate from the external carotid artery. The lower portion of the pharynx is supplied by pharyngeal branches from the inferior thyroid artery, which originates from the thyrocervical trunk of the subclavian artery.
The venous drainage of the pharynx involves a plexus that drains into the pterygoid plexus superiorly and the facial and internal jugular veins inferiorly. The pharyngeal nervous plexus, formed by the vagus (CN X) and glossopharyngeal (CN IX) nerves, is responsible for the innervation.