Pharyngeal Plexus and Pharynx Anatomy

Pharyngeal Plexus

• Stylopharyngeus muscle is the only muscle in the pharynx that is not supplied by the pharyngeal plexus.
• The pharyngeal plexus is formed by the glossopharyngeal nerve and the vagus nerve.
• The pharyngeal plexus supplies all the longitudinal and constrictor muscles of the pharynx.
• The stylopharyngeus muscle is supplied by the glossopharyngeal nerve.

Pharynx

• The pharynx is a funnel-shaped muscular tube that is about 13 cm long.
• The pharynx is located behind the nasal and oral cavity, and extends from the base of the skull (specifically, the pharyngeal tubercle) to the lower border of C6.
• The pharynx is involved in both digestion and respiration.
• The pharynx is divided into three parts: nasopharynx, oropharynx, and laryngopharynx.

Nasopharynx

• The nasopharynx is the uppermost part of the pharynx.
• The nasopharynx is located behind the nasal cavity and extends to the soft palate.
• The nasopharynx contains the pharyngeal tonsil (adenoids).
• The pharyngeal tonsil can become enlarged due to viral infections of the upper respiratory tract.
• Enlarged adenoids can obstruct the opening of the Eustachian tube, leading to chronic otitis media.
• The Eustachian tube is also known as the auditory tube.
• The Eustachian tube connects the nasopharynx to the middle ear, and helps to balance the pressure between the ear and the outside.
• The nasopharynx has a space called the pharyngeal recess, which is located behind the torus tubarius.
• The nasopharyngeal isthmus is the opening between the nasopharynx and the oropharynx.

Oropharynx

• The oropharynx is the middle part of the pharynx.
• The oropharynx is located behind the oral cavity and extends down to the epiglottis.
• The oropharynx contains the palatine tonsils.

Laryngopharynx

• The Laryngopharynx is the lowermost part of the pharynx.
• The Laryngopharynx is located behind the larynx and extends down to the esophagus.
• The laryngopharynx contains the epiglottis and the larynx.

Pharyngeal Wall

• The pharynx is protected by a wall called the pharyngeal wall.
• The pharyngeal wall has four layers:
  • Mucosa: The innermost layer, composed of mucous membrane.
  • Submucosa: A layer of connective tissue that separates the mucosa from the pharyngeal aponeurosis.
  • Pharyngeal aponeurorsis: A thick fibrous sheath that is the strongest part of the pharyngeal wall and provides attachment for the constrictor muscles. This layer is continuous with the buccopharyngeal fascia which covers the pharynx.
  • Adventitia: The outermost layer, made of loose connective tissue, and is continuous with the adventitia of the esophagus.

Pharyngeal Muscles

• There are two types of pharyngeal muscles: constrictor muscles and longitudinal muscles.

• The constrictor muscles are responsible for constricting the pharynx during swallowing.

  • The constrictor muscles include the superior, middle, and inferior constrictor muscles.

• The longitudinal muscles are responsible for elevating the pharynx during swallowing.

• The longitudinal muscles include the palatopharyngeus, the stylopharyngeus, and the salpingopharyngeus.

Esophagus

• The esophagus is a muscular tube that is about 25 cm long.
• The esophagus extends from the lower end of the pharynx at the lower border of the cricoid cartilage to the stomach.
• The esophagus begins opposite the body of the 6th cervical vertebra.
• The esophagus passes through the diaphragm at the level of T10.
• The esophagus has a number of constrictions along its length.
  • The narrowest part of the esophagus is at the level of the cricoid cartilage, also known as the cricopharyngeal constriction.
  • The second constriction is at the aortic arch, at the level of T4.
  • The third constriction is at the left main bronchus at the level of the intervertebral disc between T4 and T5.
  • The fourth constriction is at the diaphragm.
  • These constrictions are significant as they are potential sites of obstruction.

Esophageal Sphincters

• The esophagus has two physiological sphincters:
  • The Upper Esophageal Sphincter
  • The Lower Esophageal Sphincter
• These sphincters are made of smooth muscle.
• The upper esophageal sphincter is located at the junction of the pharynx and the esophagus.
• The lower esophageal sphincter is located at the junction of the esophagus and the stomach.
• These sphincters prevent the entry of air into the esophagus and the reflux of gastric contents into the esophagus.

Otitis Media

• Inflammation of the nasopharynx (specifically, the pharyngeal tonsil/adenoids) can lead to otitis media.
• This is because the Eustachian tube connects the nasopharynx to the middle ear.
• When adenoids are enlarged, they can block the Eustachian tube, preventing proper drainage of the middle ear and leading to infection and inflammation.

Diverticulum

• The inferior part of the pharynx can be a common site for diverticulum formation.
• The inferior constrictor muscle is made up of two parts that are separated from each other by a gap.
• This gap is not covered by muscle and is only covered by mucous membrane, making it a weak area.
• This weak area is prone to diverticulum formation.