Pharynx - Anatomy & Physiology

Introduction

Developing Head - Copyright RVC

The pharynx is part of both the respiratory and digestive system. Both systems have entrances to the pharynx but they are separated from each other by the soft palate. During exercise or during respiratory distress, the mouth can be used as an additional opening of the respiratory system and then the oropharynx also becomes an air-way.

The pharynx can be split into different regions- the oropharynx, laryngeal pharynx (sometimes referred to as the oesophageal pharynx) and the nasopharynx.

Nasopharynx Anatomy - Copyright RVC

Structure and Function

The opening of the larynx is on the floor of the pharynx. Caudal and dorsal to the laryngeal opening is the opening into the oesophagus. In the dorsal region of the nasopharynx there are paired openings into the auditory (eustacian) tubes. The lining of the middle ear cavity and auditory tube is continuous with that of the nasopharynx. It is located between the base of the skull and the first two cervical vertebrae dorsally and the larynx ventrally. The mandible, pterygoid muscles and hyoid apparatus are located laterally. Laterally, two pairs of palatopharyngeal arches are present from the soft palate to the oesophagus.

Pharynx Labelled - Copyright C.Clarkson and T.F.Fletcher University of Minnesota

The walls of the pharynx contain striated muscle. During swallowing, the soft palate is raised which divides the pharynx into dorsal and ventral sections. The dorsal compartment is the nasopharynx and the rostral compartment is the oropharynx. The laryngeal pharynx is separated from the oropharynx by the epiglottis. Tonsils are present on the lateral walls of the oropharynx and are covered by flaps of mucosa. It is partially visible in the open mouth.

The pharynx plays an important role in deglutition.

Soft palate dividing the oropharynx and the nasopharynx - Copyright RVC

Musculature

Muscles that constrict

Muscles that constrict run dorsally to the roof of the pharynx. Rostral constrictor muscles are the hyopharyngeous, pterygopharyngeous and the palatopharyngeous muscles. They originate from the pterygoid region of the skull and the aponeurosis of the soft palate and shorten the pharynx. The middle constictor muscle is the thyopharyngeous muscle. It origniates from the hyoid bone. The caudal constictor muscle is the cricopharyngeous muscle. It originates from the thyroid cartilage of the larynx.

Muscles that dilate

Muscles that dilate enclose the pharynx laterally and dorsally. The dilator muscle is the stylopharyngeous muscle. It originates from the hyoid apparatus and widens the rostral pharynx.

Muscles that shorten

The pterygopharyngeal muscle and palatopharyngeal muscle shorten the pharynx. They enclose the pharynx laterally and dorsally.

Muscles that close the Pharyngeal Arch

The palatopharyngeous muscle also closes the pharyngeal arch.

Innervation

Pharyngeal muscles arise from arch 4

Pharyngeal branch of the vagus nerve (CN X) from the cranial root of the accessory nerve (CN XI)

Stylopharyngeous muscle comes from arch 3 and is innervated by the accessory nerve (CN XI)
Glossopharyngeal nerve (CN IX) supplies taste to the pharynx