Pharynx and its parts

The pharynx is a muscular, funnel-shaped organ, about 10 to 14 cm long. It lies behind the oral and nasal cavities. The pharynx is an anatomical structure where both air and food passages intersect. Therefore it belongs to both the respiratory and gastrointestinal tracts.

It may be divided into three parts:

• Nasopharynx
• Oropharynx
• Laryngopharynx

Innhaled air through the nose first reaches the nasopharynx, then the oropharynx, and next flows into the larynx via the laryngopharynx. On the other hand, food is transported from the oral cavity via the oropharynx and laryngopharynx into the esophagus.

The nasopharynx is the nasal part of the pharynx. It is the most upper part or superior division of the pharynx, and it is located at the first and second cervical vertebrae level (C1-C2), posterior and inferior to the nasal cavity. This part extends from the external cranial base to the free edge of the soft palate.

The upper part of the nasopharynx is firmly connected with the body of the sphenoid bone. The connection is known as the vault of the pharynx or pharyngeal fornix.

There is an opening in the wall of the nasopharynx that leads to the auditory tube, which connects the pharynx with the tympanic cavity. 

The pharynx also houses lymphatic tissue masses called tonsils, including the:

• Pharyngeal tonsil - located in the nasopharynx;
• Two tubal tonsils (right and left) - located in the nasopharynx;
• Two palatine tonsils (right and left) - located in the oropharynx;
• Lingual tonsil - in the oropharynx.

Muscles of the pharynx

The pharynx contains two groups of very well-developed skeletal muscles. 

All muscles have pairs, and the following groups are:

• Muscles constricting the pharynx or circular muscles
• Longitudinal muscles or the muscles that lift the pharynx

Muscles of the pharynx, together with the tongue, soft palate, and larynx help to move and swallow the food as the soft palate elevates and closes the passage to the nasal cavity. Epiglottis depresses and closes the airways, allowing to move the food by tongue and pharynx muscles further in the esophagus.

Constrictor muscles are the:

• Superior pharyngeal constrictor
• Medial pharyngeal constrictor
• Inferior pharyngeal constrictor

Levator muscles are the:

• Stylopharyngeus 
• Palatopharyngeus 
• Salpingopharyngeus
  

Blood supply

The arterial blood supply for the pharynx is provided by the:

• Ascending pharyngeal artery - a branch of the external carotid artery;
• Dorsal lingual branch - from the lingual artery;
• Ascending palatine artery - from the facial artery;
• Tonsillar branches - from the facial artery;
• Small pharyngeal branches - from the inferior thyroid artery;
• Maxillary artery and its branches (greater palatine, pharyngeal and pterygoid arteries).

Venous drainage for the pharynx provides the pharyngeal plexus carrying blood next to the facial and pharyngeal veins and then to the internal jugular vein.

Innervation

Sensory and motor innervation is mainly provided by the pharyngeal plexus. It is made by the pharyngeal branches of the glossopharyngeal nerve (CN IX), vagus nerve (CN X), and fibers from the superior cervical ganglion of the cervical part of the sympathetic trunk.

Motor innervation

All pharyngeal muscles, except the stylopharyngeus muscle, are innervated by the fibers of the vagus nerve (CN X). 

Stylopharyngeus muscle gets nerve supply from the same-named branches of the glossopharyngeal nerve (CN IX).

Sensory innervation

As mentioned above, mainly the pharynx receives the sensory innervation from the glossopharyngeal nerve (CN IX). 

The upper nasopharynx part is innervated by the branches of the maxillary nerve (CN V2).