Pharynx: Muscles, Layers, Nerve Supply, Parts of Pharynx

Pharynx is a part of the gastrointestinal system. It is a muscular tube starting from the base of the skull and extends upto the level of C6 vertebra in posterior relation. It starts at the end of mouth and continues downwards as an esophagus. The main role of the pharynx for the gastrointestinal tract is  swallowing of the food and serve as a tract for food to move from mouth towards the esophagus.

Muscles of Pharynx

• The pharynx consists of the following muscles ( 3 constrictors and 3 elevators):
• Three constrictors namely- Superior, middle and inferior pharyngeal constrictors.
• Three elevators namely - Salpingopharyngeus muscle, Stylopharyngeus muscle and palatopharyngeus muscle.
• The muscles are arranged to assist the process of swallowing.The constrictors are located on the outside and elevators are on the inside of the wall.
• The salpingopharyngeus muscle is the one that comes from the eustachian tube.
• The stylopharyngeus muscle is the other muscle that comes from the styloid process.
• The palatopharyngeus muscle is the third one and it comes from the palate.
• The muscles of the pharynx are controlled by Nucleus ambigus which is present in the brain stem.

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Layers of Pharynx

• It is a part of the gut tube, the lumen has 4 layers :
  • Mucosa
  • Contains pharyngobasilar fascia
  • Muscularis externa
  • Connective tissue buccopharyngeal fascia 
• 6 layers in muscles :
  • 3 are constrictors (described above) - These are circular in arrangement.
  • 3 are elevators - These are longitudinal in arrangement.

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Nerve supply

• The Glossopharyngeal nerve supplies the stylopharyngeus , vagus and accessory nerve supply all the pharynx muscles.
• The axons of the cranial accessory nerve are carried by branches of the vagus called vagus accessory complexes and those axons leave the vagus nerve by the branches called pharyngeal branches of the vagus to form the pahryngeal plexus.
• The nasophaaryngeal nerve is the sensory supply to the pharynx as it stimulates the post-pharyngeal wall.
• The sensation carried by the glossopharyngeal nerve will reach the Nucleus Tractus Solitarius which will then activate the nucleus ambiguous and the nucleus ambiguous by the vagus accessory complex will then cause contraction of the muscles of the pharynx, not only of the pharynx but the palate, pharynx and larynx.
• The superior, middle and inferior pharyngeal constrictors , there will be one on each side , right and left and these muscles cover the pharynx posterolaterally.
• In the pharynx, there is no anterior wall in the rose and the oral cavity region.
• The pharynx is divided into three parts( behind the nose ) :
  • Nasopharynx
  • Oropharynx
  • Laryngopharynx

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Part of the Pharynx

• It starts from the base of the skull about 12 cm in length and it has  3 parts reaching to the lower border of the cricoid cartilage larynx and level of C6 vertebra.
• Nasopharynx - It is an opening in the nasal cavity. In the nasopharynx, there is an opening of the eustachian tube, tonsil MALT ( mucosa associated lymphoid tissue) , Waldeyer’s lymphatic ring, the palatine tonsils, nasopharyngeal tonsil (adenoid) and lingual tonsil. It constitutes choanae with nasal conchae , tubal elevation and opening of auditory eustachian tube.
• Oropharynx - It is an opening in the oral cavity.
• Valicula- It is a space with one on the right side and the other on the left side lying on the midline of the glossoepiglottic.
• Laryngopharynx- It is the part below the larynx.  It is laryngeal inlet .There is a hidden fossa where supraglottic carcinomas are missed clinically . It is a postcricoid area.
• Pyriform fossa- It will be in pyriform shape; one end is wide and the other hand is narrow; it is the 10^th nerve supplying the laryngopharynx. Inferior turbinate the largest of the turbinates . The opening of the Eustachian tube is 1.25 cm behind the posterior to inferior turbinate in the nasopharynx. The opening of the Eustachian tube is 1.25 cm behind the posterior to inferior turbinate in the nasopharynx. Pharyngeal tonsil and tubal tonsil are present in the nasopharynx. Palatine tonsil and lingual tonsil are present in the oropharynx. 

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