Pharynx

Parts of the pharynx have been identified when the carotid triangle of the neck was discussed. Now that the head and cervical viscera have been separated, you can identify the pharyngeal muscles and the structures that lie lateral to them.

The muscles of the pharynx consists of three pharyngeal constrictors:

  • superior
  • middle
  • inferior
and the stylopharyngeus and palatopharyngeus muscles.

The three constrictors are nested within each other from the top down. You might visualize the constrictors as three cone-shaped cups fitting within each other. The superior fits into the middle which fits into the inferior. The only thing wrong with this picture is that the cups are open on one side. These openings are the nasal cavity, oral cavity and the larynx. Now take a look at the pharynx from the back.

 

When you first observe the back of the pharynx, you will want to identify the structures that run parallel to its lateral surface:
  • glossopharyngeal nerve (IX)
  • vagus (X)
  • spinal accessory nerve (XI)
  • hypoglossal nerve (XII)
  • common carotid artery (CC)
  • internal jugular vein (IJ)
  • carotid sheath (CS)
In this image, the carotid sheath and its contents has been removed in order to show the stylopharyngeus muscle (SP). One reason to be able to identify the stylopharyngeus muscle is that the glossopharyngeal nerve (IX) runs along its posterior surface and can always be identified at this point. The stylopharyngeus muscle also extends between the superior and middle pharyngeal constrictors and can be used to separate these two muscles.
Finally, identify the three pharyngeal constrictors. Before identifying the pharyngeal constrictors, you should first memorize their origins and then you won't have trouble picking them out during a dissection or an examination.

The superior pharyngeal constrictor (SC) arises from the hamulus of the medial pterygoid plate and the pterygomandibular raphe which extends from the hamulus to the lingula of the mandible. This origin is not easy to point out so you will usually identify the other two constrictors first.

The middle pharyngeal constrictor (MC) arises from the greater horn of the hyoid bone (GH). This structures can always be seen or felt.

The inferior pharyngeal constrictor (IC) arises from the thyroid and cartilages which are also obvious structures.

The inferior pharyngeal constrictor continues as the esophagus (ES).

The constrictors join in the mid line posteriorly as a seam (pharyngeal raphe) which is suspended form the pharyngeal tubercle on bottom of the occipital bone.

We will cover the nerve supply of the pharynx later.

 


 
Along the lateral sides of the pharynx, you will find four gaps associated with the superior, middle and inferior constrictors. Specific structures pass through each of these gaps.

Above the superior pharyngeal constrictor:

  1. auditory tube (AT)
  2. levator palati (LP)
  3. ascending palatine artery (APA)
Between the superior and middle constrictors:
  1. stylopharyngeus muscle (SP)
  2. glossopharyngeal nerve (IX)
Between the middle and inferior constrictors:
  1. internal laryngeal branch of the superior laryngeal nerve (IL)
  2. superior laryngeal artery from the superior thyroid artery (SLA)
Below the inferior constrictor:
  1. inferior laryngeal nerve ( ILN) (recurrent laryngeal branch of the vagus)
  2. inferior laryngeal artery (ILA) (inferior thyroid)

Pharyngeal Cavity as Viewed From the Back

After the pharynx has been cleaned from the back and the pharyngeal constrictors are identified, the pharynx can be opened and the anterior relationships exposed. 
What you should be able to identify are:
 
  • nasopharynx (arrow)
  • oral pharynx (where tongue is seen)
  • laryngeal pharynx (larynx).
If you inserted you finger into each one of these, you would enter the nasal cavity, oral cavity and larynx from behind. To have another view of this same relationship, see the following section.

 

Sagittal Section of the Head and Neck

There comes a point in the anatomy laboratory when the body must be divided into strange sections in order to study its innermost parts. One of these divisions is the sagittal section of the had and neck. This will aid in the visualization of the nasal cavity, oral cavity and the larynx. Once smaller pieces of the head and neck are produced, it becomes difficult to know what is anterior, posterior, up or down. You should make it a habit to pick out a structure that you can always identify (such as the mandible, tip of nose, tip of tongue, etc.) and use this to give you the proper orientation. Every time you walk up to a cadaver, or look at an image, the first thing to do is orient yourself. Orientation is very important!!!
Once the head and neck have been separated into left and right halves, you can see relationships of the nasal cavity, oral cavity and larynx to the pharynx. These cavities function as part of the respiratory and gastrointestinal systems. You will notice in the diagram that the two systems merge. I am sure that most of you have experienced choking after inhaling fluid or food instead of swallowing it.
Air flows through both the nasal cavity and oral cavity to travel through the nasopharynx and oropharynx respectively before entering the larynx.
Food travels through the oropharynx, down the laryngopharynx and into the esophagus. The innervation to this area, both motor and sensory, is important in keeping the pathways functioning properly. We will cover the nerve supply in future sessions.
Remember to orient yourself when you look at these images.
I usually use the mandible (M) or maxilla (Mx) as a starting point. Then I look for the tip of the tongue or tip of the nose.
Once oriented with the sagittal section, identify the nasal cavity, the oral cavity with the tongue, the epiglottis and larynx.
The borders of the naso-, oro-, and laryngopharynges are arbitrary and shown as red dotted lines in the diagram. Classically, the anterior border of the opening of the auditory tube and tip of uvula for the nasopharynx, the palatoglossal fold and upper border of epiglottis for the oropharynx and the opening of the larynx for the laryngopharynx. Nasopharynx (np), oropharynx (op), and laryngopharynx (lp).
Posterior to the pharynx, you can identify the atlas (C1), axis (C2) and the remaining cervical vertebrae. You can also see the spinal cord passing through the vertebral canal (yellow).

Innervation of the Pharynx

Motor Innervation
  1. glossopharyngeal (IX)
  2. vagus (X) and allied spinal accessory (XI)
  3. recurrent laryngeal
Sensory Innervation
  1. glossopharyngeal (IX to oropharynx region
  2. vagus (X) to remainder of pharynx
Lateral Pharyngeal Region   Nasal Cavity, Oropharynx, Tonsil


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