Lab Manual - Carotid Sheath, Pharynx, & Larynx

Learning Objectives:

Upon completion of this session, the student will be able to:

  1. Review the arrangement, distribution and function of the cervical sympathetic trunk. (explanation)
  2. Review the carotid sheath and contents. (explanation)
  3. Identify, trace and describe the general functions of cranial nerves IX (glossopharyngeal), X (vagus), XI (spinal accessory), XII (hypoglossal). (explanation)
  4. Describe the pharynx, its anatomical architecture and action of its musculature during swallowing. (explanation)
  5. List the basic functions of the larynx. (explanation)
  6. Describe the anatomy of the interior of the larynx. (explanation)
  7. Identify the main cartilages and membranes that form the internal framework (skeleton) of the larynx. (explanation)
  8. Describe the actions of the intrinsic muscles of the larynx in tensing, relaxing, abducting or adducting the vocal folds. (explanation)
  9. Describe the innervation and vascular supply of the larynx. (explanation)

Readings and Modules:

Procedure:

1. Review the osteology of the pharynx, larynx and hyoid bone. (Play movie; View images: N 4, 6, 8, 13, 77A, 77B, TG 7-06, 7-08, 7-09, 7-25, 7-28, 7-32)

On the base of a skull locate the following structures: pharyngeal tubercle, medial pterygoid plate, pterygoid hamulus. On the hyoid bone identify body, greater and lesser cornua (horns). Identify the thyroid cartilage, the cricoid cartilage and the arytenoid cartilage.

2. Open the retropharyngeal space and identify the cervical sympathetic trunk. (Play movie; View images: N 35, 130, TG 7-10, 7-15)

On the right side, identify the retropharyngeal space and open it completely from the base of the skull to the root of the neck using blunt dissection. Identify the cervical sympathetic trunk, and bluntly reflect it anteriorly with the neck viscera and away from the vertebral column, scalene muscles, and cervical ventral primary rami. Cut gray rami communicantes between the sympathetic trunk and cervical ventral rami on the right side only. On the contralateral (left) side, use a lateral approach to identify the retropharyngeal space and the sympathetic trunk by elevating the carotid sheath structures and the neck viscera.

3. On the right, disarticulate the atlanto-occipital joint. (Play movie; View images: N 21, 34, 35, 73, TG 1-09, 7-10, 7-17, 7-21)

On the right side only, identify the atlas and the margins of the foramen magnum and cut through dura and ligaments connecting the atlas to occipital bone (be careful not to cut too far anteriorly). Extend this incision posteriorly, severing all neck muscles posterior to the mastoid process. Twist the head on the vertebral column, insert a chisel between atlas and occipital condyle and pry the skull forward; sever ligaments and muscles at the base of the skull as necessary until the vertebral column and scalene muscles are removed. Avoid cutting into the back of the pharynx or carotid sheath. After removal of the vertebral column, observe the posterior surface of the neck viscera and carefully remove the buccopharyngeal fascia to expose the back of the pharynx.

4. Clean the cervical sympathetic trunk, vagus nerve, carotid arteries and internal jugular vein. (Play movie; View images: N 8, 73, 75, 125A, 125B, 130, 131, TG 7-06, 7-14, 7-15, 7-20, 7-21, 7-71, 7-72, 7-90, 7-92, 7-95)

Clear the fascia of the carotid sheath from the contained nerves and vessels. These contents enter or exit the skull through the external opening of the carotid canal and the jugular foramen, and are located medially and dorsally (behind) the styloid process in a space referred to as the retrostyloid space.

Identify and trace each of the following:

Do you find any lymph nodes (retropharyngeal)?

5. Identify and trace the glossopharyngeal, accessory, and hypoglossal nerves. (Play movie; View images: N 32, 67, 71A, 71B, 125, 127, 128, TG 7-17, 7-18, 7-20, 7-21, 7-90, 7-93, 7-94)

Identify and trace each of the following:

6. Clean and identify the muscles of the pharynx and pharyngeal plexus. (Play movie; View images: N 13, 35, 67, 68, 77, 125, 126, 130, 131, TG 7-09, 7-10, 7-21, 7-25, 7-26, 7-90, 7-92)

Consider components of the pharyngeal plexus of nerves and the pharyngeal musculature. Carefully remove the buccopharyngeal fascia, the pharyngeal plexus of veins and any loose connective tissue overlying this musculature. Palpate and locate the greater horn of the hyoid bone and the superior horn of the thyroid cartilage. Define the three pharyngeal constrictor muscles (superior, middle, and inferior) and trace each as close to its origin as possible. Observe the pharyngobasilar fascia forming the pharyngeal wall above the superior pharyngeal constrictor. What tissue is it? Note the shape of the different parts of the pharynx. Clear the stylopharyngeus muscle and trace to the pharynx. Between what two muscles does it pass? Note the beginning of the esophagus, arrangement of musculature, and attachment. Consider the complete blood supply to pharyngeal constrictors. Innervation?

7. Examine the pharyngeal and laryngeal cavities, noting their regions and prominences. (Play movie; View images: N 41, 62, 64, 66, 67, 69, 70, TG 7-22, 7-23AB, 7-23C, 7-39, 7-41)

Define nasal, oral and laryngeal portions of pharynx. What boundaries separate these regions?

Nasopharynx: Identify the choanae, soft palate and uvula, torus tubarius, pharyngeal recess, and the pharyngeal tonsil.

Oropharynx: Identify the palatoglossal and palatopharyngeal folds, tonsillar fossa, and palatine tonsil (if present). Remove one tonsil from its bed or fossa. What structures lie immediately deep (lateral) to it? Identify the glossopharyngeal nerve as it passes to the base of the tongue, inferior to the palatine tonsil. Where is the lingual tonsil? Identify the glossoepiglottic folds.

Laryngopharynx: Identify the epiglottis, which divides the oropharynx from the laryngopharynx, laryngeal inlet, piriform recesses and entrance to the esophagus.

Structures of the pharynx and larynx

8. Dissect the larynx, its membranes, muscles, ligaments, vessels and nerves. (Play movie; View images: N 15, 67, 69, 70, 74, 75, 76, 77A, 77D, 78, 80, 81A, 81E, 82C, 82D, 83, 84A, 84B, 126, 233, 235, TG 7-09, 7-19, 7-20, 7-21, 7-22, 7-23, 7-25, 7-26A, 7-26B, 7-26C, 7-27A, 7-27B, 7-28A, 7-28B)

Note and palpate the cartilages of the larynx (thyroid, cricoid, epiglottic and arytenoid), their parts, spatial relationships, and their manner of articulating with one another. Palpate and examine the hyoid bone and review its parts. The cartilages of the larynx along with their articulations and membranes constitute a separate, almost independent, musculoskeletal entity. What structural features differ in male and female?

Note the articulation between the inferior horn of the thyroid cartilage and the cricoid cartilage (cricothyroid joint). This is a true synovial joint with a joint cavity, capsule and ligaments. What is the action of this joint?

Examine the sectioned larynx and identify: epiglottis, aryepiglottic folds, interarytenoid notch, laryngeal inlet or aditus (entrance to larynx), vestibule of larynx, piriform recess. Examine the epiglottic cartilage and consider its function during swallowing. Palpate the arytenoid cartilages and the lamina of the cricoid cartilage. Move the arytenoid cartilage around, noting the presence of a cricoarytenoid joint.

Define the spaces: vestibule, ventricle, rima glottidis, and infraglottic portion of the laryngeal cavity. What is the glottis?

Strip the mucosa from the dorsal surface of the larynx (anterior mucosa of laryngopharynx). Now locate the cricothyroid articulation and identify the inferior laryngeal nerve (note name change) and the inferior laryngeal artery. What is the source of each? Trace them into the piriform recess. Note motor branches and communications with the internal branch of the superior laryngeal nerve. Clean off the posterior cricoarytenoid and arytenoideus muscles (transverse and oblique fibers).

In the interior of the larynx, observe the full extent of the quadrangular membrane and conus elasticus. Identify the vocal process of the arytenoid cartilage. Define the vocal ligament. Note how the quadrangular membrane and conus elasticus plus the mucosa constitute the lining of the interior of the larynx. In addition, identify the vestibular fold (false vocal fold) and vocal fold (true vocal fold).

On one side, carefully remove the thyroid lamina by cutting through the cricothyroid joint. Cut its attachment to the thyrohyoid membrane and muscles. With the thyroid lamina removed, identify the thyroarytenoid muscle and the lateral cricoarytenoid muscle.

Lift the posterior border of the thyrohyoid muscle to expose the thyrohyoid membrane. Determine its extent and attachments. Identify two structures that perforate the membrane: the internal branch of the superior laryngeal nerve and the superior laryngeal artery. What is the source of each? Identify these within the piriform recess. Now clean the cricothyroid muscle and identify the external branch of the superior laryngeal nerve to it. Does the nerve pass through or give off a branch to the inferior pharyngeal constrictor muscle? Trace both nerves to the superior laryngeal nerve of the vagus. Deep to the cricothyroid muscle is a thick elastic membrane, the conus elasticus; note its median cricothyroid ligament.