Pharynx

=**Objectives**=


 * 1. Explain the anatomical location and functional significance of the pharynx.**

The pharynx is a fibromuscular tube that lies anterior to the vertebral column extending from the superior base of the skull and blending inferiorly with the esophagus. It serves as a common passageway for the GI tract and the respiratory system. It begins at the posterior aperture of the nose and ends at the esophagus. There are three regions of the pharynx identified by the three cavities that it is continuous with: nasopharynx, oropharynx, and laryngopharynx.

There are five layers composing the wall of the pharynx: the mucus membrane, submucosa, pharyngeal basilar fascia, muscular layer, and buccopharyngeal fascia. The mucous membrane is continuous with whatever cavity it is coming from. The pharyngeal basilar fascia is a fibrous layer of dense connective tissue that goes from the occipital bone where it is thickest to the esophagus where it tapers out. The muscle layer contains the six pairs of pharyngeal muscles. The buccopharyngeal fascia lies anterior to the retropharyngeal space and the vertebral column.


 * 2. Give the boundaries of each of the three portions of the pharynx and list any important structures located in each of these areas.**

The three portions of the pharynx are the nasopharynx, the oropharynx, and the laryngopharynx.

__Nasopharynx__ The nasopharynx extends from the skull to the C2 vertebral level and is superior to the soft palate. This is the most superior portion of the pharynx and lies posterior to the nasal cavity.

The two choanae are the posterior nasal apertures separated by the nasal septae that delineate the border between the nasal cavity and the nasopharynx.

There is a tubal elevation of mucus membrane overlying the medial end of the auditory tube.

The auditory or Eustachian tubes are nasopharyngeal tubes extending from the nasopharynx to the middle ear and have a bony and a cartilaginous portion. The bony portion is lateral and goes towards the middle ear; the cartilaginous portion is medial and goes towards the nasopharynx. The whole tube is lined with mucous membrane. It functions to equalize the pressure of the middle ear with the outside environment; several of the pharyngeal muscles attached to it can pull down on the tube to make it more patent.

The pharyngeal tonsils or adenoids are a collection of lymphoid tissue that lies under the mucus membrane on the posterior wall of the nasopharynx. When inflamed, it can block off the nasal cavity.

__Oropharynx__ The oropharynx extends from the C2 to the C4 vertebral level. Its inferior limit is the epiglottis. It lies posterior to the oral cavity and is separated from it by the palatoglossal arches. The palatoglossal arches are the anterior arches, deep to which lie the palatoglossal muscle. The palatopharyngeal arches are the posterior arches, deep to which lie the palatopharyngeal muscle. The palatoglossal and palatopharyngeal muscles form a tonsilar bed where the palatine tonsils lie in between.

__Laryngopharynx__ The laryngopharynx extends form the C4 to the C6 vertebral level. The laryngopharynx lies posterior to the larynx and stretches laterally on both sides, forming two recesses. These recesses are called the piriform recesses. During swallowing, the bolus travels posterior and laterally around the larynx. Occasionally, the bolus can get caught in a piriform recess and require intervention by a laryngoscope which is oodles of fun.


 * 3. What is the functional significance of the auditory tube? Where is it located?**

The auditory tubes or Eustachian tubes opens under the tubal elevations of the nasopharynx. The auditory tube has clinical significance in otitis media where an infection can reach the middle ear from the upper respiratory tract through the auditory tube (See Histology of the Ear). This is especially important in infants who have a much shorter, straighter auditory tube than adults. Because the middle ear and the tympanic membrane are innervated by the glossalpharyngeal nerve (CN IX), these infections tend to be painful.


 * 4. Explained the location(s) of the lymphoid tissue found in the pharynx. Why is it important?**

The pharyngeal tonsils or adenoids are located under the mucus membrane on the posterior wall of the nasopharynx. It is a collection of lymphoid tissue that, when inflamed, can block off the nasal cavity, making breathing uncomfortable and affecting the voice so that you sound funny.

The palatine tonsils are found under the mucus membrane on the oropharynx between the palatoglossal and palatopharyngeal arches and their underlying muscles. These are the tonsils that can be seen in the back of the throat. When inflamed, these tonsils often cause a sore throat.

The palatine tonsils and tonsilar bed are supplied by the tonsilar artery branch of the facial artery. This is clinically relevant during tonsillectomy where it is necessary to ensure cauterization of the tonsilar artery. Kids who get tonsillectomies are encouraged to eat popsicles and ice cream to prevent unnecessary abrasion to the scab of the cauterized tonsilar artery.


 * 5. Explain how the muscles of the pharynx are organized. Give general origins and insertions for these muscles, as well as their actions.**

There are //six pairs of muscles// of the pharynx organized into three constrictors and three longtitudinal muscles.

__Constrictor Muscles__ The constrictors are semicircular muscles named superior, middle, and inferior constrictor. These muscles overlap each other and all insert on the midline raphe and forma fibrous band.

The superior constrictor originates on the pterygomandibular raphe, medial pterygoid plate, the body of the mandible and the occipital bone and inserts on the midline raphe. Its broad origin on the medial pteyrgoid plate to the mandible highlights the secondary function of the superior constrictor to close off the oral cavity. Its origin on the occipital bone is not complete, attaching only on the lateral sides and in the middle, leaving two areas that are closed off by pharyngeal basilar fascia.

The middle constrictor originates on the hyoid bone and the stylohyoid ligament, inserting to the midline raphe.

The inferior constrictor originates on the thyroid and cricoid cartilages and insert on the midline raphe..

The action of all the constrictor muscles is to constrict the pharynx via sphincter action to help move the bolus inferiorly.

__Longitudinal Muscles__ The three pairs of longitudinal muscles are the salphingopharyngeous muscle, the stylopharyngeous muscle, and the palatopharyngeous muscle.

The salphingopharygenous muscle originates from the posterior part of the auditory tube and blends with the pharyngeal wall where it joins up with the palatopharyngeous muscle.

The stylopharyngeous muscle originates on the styloid processs and passes between the space between the superior and middle constrictors and then blends with the pharynx wall.

The palatopharyngeous muscle originates on the soft palate, and inserts by blending with the pharynx wall.

The longitudinal muscles act to elevate, shorten, and widen the pharynx and larynx during swallow and speaking. The salphingopharynx also helps pull on the auditory tube to make it more patent, facilitating equalization of pressure of the middle ear with the outside environment.

__Innervation__ The superior, middle, and inferior constrictor muscles, salphingopharyngeus muscle, and the palatopharyngeous muscle are all motor innervated by the vagus nerve (CN X). The stylopharygneous muscle is the only one of the pharyngeal muscles that is instead motor innervated by the glossopharyngeal nerve (CN IX).

The mucus membrane of the pharynx receives sensory innervation by the glossopharyngeal nerve (CN IX). The lower portion of the pharyngeal wall receives sensory innervation from the internal laryngeal branch of the vagus nerve (CN X).

The maxillary nerve (CN V2) provides sensory innervation to the naspharynx and some to the oropharynx. The sympathetic fibers from the superior cervical ganglion provide vasoconstriction innervation to the blood vessels of the pharynx. The parasympathetic fibers from the facial nerve (CN VII) and vagus nerve (CN X) contribute to secreomotor innervation to the mucus membrane.

__Blood Supply__ The pharynx receives several blood vessels which contribute to supplying the walls of the pharynx including the ascending pharyngeal artery, the branches of the maxillary artery, the branches of the facial artery including the tonsilar branch, and the superior and inferior thyroid arteries.


 * 6. Give all the components of the pharyngeal plexus.**

The pharyngeal plexus is a network of nerve fibers located on the surface of the middle pharyngeal constrictor muscle recieving innervation from:
 * 1) vagus: motor innervation (CN X)
 * 2) Glossopharangeal: sensory (CN IX) + motor to stylopharyngeus
 * 3) CN V2: sensory to nasopharynx and some oropharynx
 * 4) Sympathetic fibers from superior cervical ganglion (innervate blood vessels)
 * 5) Parasympathetic: CN VII, CN X (innervate mucous glands)


 * 7. What is the buccopharyngeal fascia? What is the retropharyngeal space? Why are these important?**

The buccopharyngeal fascia is a a thin lamina along the medial aspect of the prevertebral fascia. It closely invests the Constrictor muscles of the pharynx, and is continued forward from the Constrictor pharyngis superior on to the Buccinator. It is attached to the prevertebral layer by loose connective tissue only, and thus an easily distended space, the retropharyngeal space, is found between them. The retropharyngeal space is limited above by the base of the skull, while below it extends behind the esophagus into the posterior mediastinal cavity of the thorax. This is a potential space that can become infected and possibly spread to the thorax.