The Pharynx

The pharynx is a muscular tube that connects the oral and nasal cavity to the larynx and oesophagus.

It begins at the base of the skull, and ends at the inferior border of the cricoid cartilage (C6). The pharynx is comprised of three parts (superior to inferior):

• Nasopharynx
• Oropharynx
• Laryngopharynx.

Nasopharynx

The nasopharynx is found between the base of the skull and the soft palate. It is continuous with the nasal cavity, and performs a respiratory function by conditioning inspired air and propagating it into the larynx.

This part of the pharynx is lined with respiratory epithelium; ciliated pseudostratified columnar epithelium with goblet cells.

The posterosuperior nasopharynx contains the adenoid tonsils, which enlarge between 3-8 years of age and then regress.

Oropharynx

The oropharynx is the middle part of the pharynx, located between the soft palate and the superior border of the epiglottis.

It contains the following structures:

• Posterior 1/3 of the tongue.
• Lingual tonsils – lymphoid tissue at the base of the tongue.
• Palatine tonsils – lymphoid tissue located in the tonsillar fossa (between the palatoglossal and palatopharyngeal arches of the oral cavity).
• Superior constrictor muscle

Waldeyer’s ring is the ring of lymphoid tissue in the naso- and oropharynx formed by the paired palatine tonsils, the adenoid tonsils and lingual tonsil.

The oropharynx is involved in the voluntary and involuntary phases of swallowing.

Laryngopharynx

The most distal part of the pharynx, the laryngopharynx is located between the superior border of the epiglottis and inferior border of the cricoid cartilage (C6). It is continuous inferiorly with the oesophagus.

It is found posterior to the larynx and communicates with it via the laryngeal inlet, lateral to which one can find the piriform fossae.

The laryngopharynx contains the middle and inferior pharyngeal constrictors.

Muscles

There are two main groups of pharyngeal muscles; longitudinal and circular.

The muscles of the pharynx are mostly innervated by the vagus nerve – the only exception being the stylopharyngeus (glossopharyngeal nerve).

Circular

There are three circular pharyngeal constrictor muscles; the superior, middle and inferior pharyngeal constrictors. They are stacked like glasses, which form an incomplete muscular circle as they attach anteriorly to structures in the neck.

The circular muscles contract sequentially from superior to inferior to constrict the lumen and propel the bolus of food inferiorly into the oesophagus.

• Superior pharyngeal constrictor – the uppermost pharyngeal constrictor. It is located in the oropharynx.
  • Originates from the pterygomandibular ligament, alveolar process of mandible and medial pterygoid plate and pterygoid hamulus of the sphenoid bone.
  • Inserts posteriorly into to the pharyngeal tubercle of the occiput and the median pharyngeal raphe.
• Middle pharyngeal constrictor – located in the laryngopharynx.
  • Originates from the stylohyoid ligament and the horns of the hyoid bone.
  • Inserts posteriorly into the pharyngeal raphe.
• Inferior pharyngeal constrictor – located in the laryngopharynx. It has two components:
  • Superior component (thyropharyngeus) has oblique fibres that attach to the thyroid cartilage.
  • Inferior component (cricopharyngeus) has horizontal fibres that attach to the cricoid cartilage.

All pharyngeal constrictors are innervated by the vagus nerve 

Longitudinal

The longitudinal muscles are the stylopharyngeus, palatopharyngeus and salpingopharyngeus. They act to shorten and widen the pharynx, and elevate the larynx during swallowing.

• Stylopharyngeus – arises from the styloid process of the temporal bone, inserts into the pharynx.
  • Unlike the other pharyngeal muscles, it is innervated by the glossopharyngeal nerve (CN IX).
• Palatopharyngeus – arises from hard palate of the oral cavity, inserts into the pharynx.
  • Innervated by the vagus nerve (CN X).
• Salpingopharyngeus – arises from the Eustachian tube, inserts into the pharynx.
  • Innervated by the vagus nerve (CN X).
  • In addition to contributing to swallowing, it also opens the Eustachian tube to equalise the pressure in the middle ear.