Lab Manual - Larynx and Neck

Assignments:

Learning Objectives:

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

  1. Identify and list the attachments, innervation and action of the muscles of the neck: sternocleidomastoid, infrahyoid muscles, scalene muscles.
  2. Identify the boundaries of the anterior and posterior cervical triangles and their subdivisions.
  3. Describe the branches of the cervical plexus.
  4. Identify the deep cervical fascia, its various component layers and the resulting compartmentalization of the neck.
  5. Locate and describe the specific features of the thyroid gland.
  6. Give the position of the parathyroid glands and consider the thyroid/parathyroid gland relationship in terms of vascular supply and surgical intervention.
  7. Identify and list the parts and branches of the subclavian artery and vein, and describe their course in the neck.
  8. In the root of the neck, locate the vagus and phrenic nerves and describe their relationships to the fascia, vessels, and viscera of the neck.
  9. Describe the anatomy relevant to subclavian vein catheterization: surface landmarks and relationships of the subclavian vein to the clavicle, 1st rib, subclavian artery, brachial plexus, parietal pleura, phrenic and vagus nerves.
  10. Identify the deep cervical lymph nodes and explain their significance.
  11. Review the arrangement, distribution and function of the cervical sympathetic trunk.
  12. Review the carotid sheath and contents.
  13. List the basic functions of the larynx.
  14. Identify the main cartilages and membranes that form the internal framework (skeleton) of the larynx.
  15. Describe the actions of the intrinsic muscles of the larynx in tensing, relaxing, abducting or adducting the vocal folds.
  16. Describe the innervation and vascular supply of the larynx.
  17. Describe the anatomy relevant to cricothyroidotomy: locate the cricothyroid membrane and describe its relationships to the thyroid and cricoid cartilages, vocal cords, cricothyroid artery, and cricothyroid muscles.

Procedure:

1. Review the bony landmarks relevant to the anterior triangle of the neck. (Play movie; View images: N 1, 2, 4, 8, 13, 15, 28, 29, 77A, 77D, 185, 419, TG 4-4, 7-01, 7-03, 7-04A, 7-05A, 7-06, 7-09, 7-12, 7-13, 7-25, 7-26)

On the cadaver, yourself, or partner, palpate the following: superior border of the clavicle; inferior border and angle of mandible, mental protuberance; jugular notch and mastoid process. Also, locate the hyoid bone, laryngeal prominence, thyroid cartilage, cricoid cartilage and trachea.

Skull structures

2. Review the bony landmarks relevant to the posterior triangle of the neck. (Play movie; View images: N 4, 6, 8, 186A, 186C, TG 7-06, 7-08, 7-32, 7-15A, 7-15B)

On the base of a skull locate the following structures: foramen magnum, occipital condyles, hypoglossal canal, jugular foramen, external opening of the carotid canal, styloid process.

Surface anatomy of the anterior neck

Examine the first rib on the skeleton and cadaver, and note grooves for the subclavian vein and artery and attachments for the scalene muscles. Review the arrangement of rib one and sternum at the entrance to the thorax (root of neck). If still present, the middle third of the clavicle should be removed for better visibility.

3. 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.

4. Remove any remaining skin in the neck region and expose the platysma. (Play movie; View images: N 26, TG 7-11, 7-16)

Using a sharp scalpel, remove the remaining skin of the neck below the mandible, being careful to preserve the delicate underlying muscle layer.

5. Reflect the platysma superiorly to expose the superficial veins and cutaneous nerves of the neck. (Play movie; View images: N 28, 31, 32A, 32B, 33, 35, 36, 74, 129, 135, 185, 256, TG 7-10, 7-11, 7-16A, 7-16B, 7-31, 7-87)

Clean and expose the platysma muscle. The platysma is a tissue-paper-thin subcutaneous muscle. Carefully reflect the muscle from the clavicle upward toward the mandible. The cervical branch of the facial nerve (CN VII) enters the muscle on its deep surface just posterior to the angle of the mandible; it will be seen better in a later dissection. Locate and trace the distribution of the great auricular, transverse cervical, lesser occipital (may not be able to see yet) and supraclavicular nerves (cutaneous branches of the cervical plexus) which emerge along the posterior border of the sternocleidomastoid muscle. Removal of the platysma exposes superficial veins of the neck in the subcutaneous tissue; however, these veins may enter and lie in the deep or investing fascia. Identify and trace the following veins: external jugular, anterior jugular, jugular venous arch and communicating veins. Are they bilaterally symmetrical in arrangement or size? Are they all present?

Read about the deep cervical fascia, its various component layers and the resulting compartmentalization of the neck, specifically: the superficial (investing) layer of deep cervical fascia, infrahyoid (muscular) fascia, visceral fascia (composed of pretracheal fascia and buccopharyngeal fascia), the carotid sheath and prevertebral fascia.

6. Identify the triangles of the neck and clean the strap muscles and reflect them to expose the ansa cervicalis and the thyroid gland. (Play movie; View images: N 28, 29, 31, 32, 127, 128, 129, TG 7-02A, 7-02B, 7-12, 7-13, 7-17)

Define the two major triangles of the neck (and their subdivisions): (1) the posterior triangle (omoclavicular or subclavian triangle and the occipital triangle); and (2) the anterior triangle (muscular, carotid, submandibular and submental triangles). If you have not already done so, on one side open the superficial layer of deep cervical fascia investing the sternocleidomastoid muscle. Expose the muscle throughout its length but do not destroy the superficial veins or nerves. Reflect it upward from its origins to the level of the hyoid bone.

Surface anatomy of the cervical triangles

The remainder of the dissection is carried out below the level of the hyoid bone. Dissect the infrahyoid (strap) muscles. The nerves and arteries enter the strap muscles on their lateral borders, so care must be taken while cleaning the muscles to preserve their nerves. It is best to clean them in the medial to lateral direction. First clean the superficial layer, composed of the sternohyoid and omohyoid muscles. Consider this layer as a musculofascial sheet, noting its continuity across the mid-line and attachments. Remove the fascia and examine individual muscles. Note the superior and inferior bellies of omohyoid, its intermediate tendon, and the attachments of bellies and tendon. Carefully clean and identify branches of the ansa cervicalis (C1-3) which innervate the muscles along their lateral borders (the origins of the ansa cervicalis will be seen later). Reflect the omohyoid laterally and the sternohyoid superiorly. Now, examine the sternothyroid and thyrohyoid muscles. Find the nerve to the sternothyroid. How does the innervation to the thyrohyoid muscle differ from the other strap muscles?

In order to expose the thyroid gland, reflect the sternocleidomastoid upward from its origins and reflect the strap muscles superiorly.

7. Open the carotid sheath to expose the associated vessels and nerves. (Play movie; View images: N 32, 34, 72, 74, 126, 226, TG 7-13, 7-14, 7-17, 7-74, 7-92)

With the sternocleidomastoid reflected, the carotid sheath becomes evident. Define it, consider its contents. Identify the ansa cervicalis and define its superior and inferior roots. The easiest way to find it is to carefully clean along the lateral margin of any of the strap muscles and identify the nerve entering it. Any nerve to a strap muscle can be followed back to the ansa. If possible trace the superior root of the ansa to the hypoglossal nerve and the inferior root to the cervical plexus (C2-3). Now open the carotid sheath below the level of the hyoid bone and identify the internal jugular vein, the common carotid artery, the beginning of the external carotid artery and the vagus nerve. You may find small cardiac nerves in the connective tissue of the sheath. These are branches of the sympathetic cervical chain or vagus nerve which end in the cardiac plexus.

Angiogram of neck vessels

Look for lymph nodes along the internal jugular vein. These belong to a chain of deep cervical nodes that drain into the venous circulation at the root of the neck. They will be mentioned again in more detail in the next dissection.

Ultrasound of a lymph node

8. Dissect the thyroid gland, its vascular supply, the recurrent laryngeal nerves and the parathyroid glands. (Play movie; View images: N 29, 31, 33, 69, 74A, 74B, 75, 76, 78A, 78B, 79, 232, TG 4-38, 7-11, 7-13, 7-14, 7-15, 7-18, 7-19, 7-21, 7-26B, 7-26C)

Examine the thyroid gland. Note the fascial investment and capsule. Identify lobes, isthmus, and if present, the pyramidal lobe (consider thyroid development). Note specific relations to overlying muscles (sternothyroid), to the trachea, cricoid and thyroid cartilages, and carotid sheath contents (common carotid artery, internal jugular vein, and vagus nerve).

Locate and trace the superior thyroid artery (a branch of the external carotid artery). Trace branches to the gland and larynx. Trace the superior thyroid vein to the internal jugular vein. Find the external branch of the superior laryngeal nerve to the cricothyroid muscle. This nerve may accompany the superior thyroid artery or approach the muscle from behind by lying on the inferior pharyngeal constrictor muscle, which it also innervates. Trauma to this nerve during thyroid surgery may result in changes in voice quality. Why?

Cut through the isthmus of the thyroid and reflect the lobes laterally from the trachea (is there a thyroidea ima artery present?). Note ligaments attaching the gland to the cricoid cartilage and trachea. Locate the middle and inferior thyroid veins draining the middle portion and inferior poles (of lobes). To what do they drain? Locate the inferior thyroid artery, looping superiorly from the thyrocervical trunk and then passing downward to approach the inferior pole of the gland from its posterior lateral surface.

Find the recurrent laryngeal nerve (of the vagus) in the tracheo-esophageal groove. This nerve is in close proximity to the inferior thyroid artery and is an important relationship in thyroid surgery. You may also find some deep cervical lymph nodes in this area.

Parathyroid glands may be noted posterior and inferior to the thyroid gland. They are usually attached to branches of the inferior thyroid artery, with superior parathyroid gland within a centimeter of where it crosses the recurrent laryngeal nerve. Inferior parathyroid is usually below the thyroid gland. They are difficult to distinguish in preserved material. Consider the importance of the thyroid/ parathyroid gland relationship in terms of vascular supply, innervation, and surgical intervention.

9. Locate the accessory nerve and the roots of the cervical plexus. (Play movie; View images: N 28, 32A, 32B, 35, 71, 72, 127, 129, TG 7-02A, 7-02B, 7-10, 7-12, 7-16, 7-17, 7-18, 7-93)

Review the boundaries of the posterior triangle and its subdivisions. Reflect the sternocleidomastoid muscle to the mastoid and you will find the accessory nerve emerging at the posterior border at or just below the upper and middle thirds of the muscle and running obliquely down to the superior border of the trapezius muscle. The nerve is usually in the superficial layer of deep cervical fascia. Remove this fascia, leaving the nerves and the external jugular vein intact. Note the course of the accessory nerve through the muscle and its relation to all of the cutaneous branches of the cervical plexus (lesser occipital, great auricular, transverse cervical, supraclavicular nerves). Now trace these nerves to their cervical origins, identifying specific ventral primary rami of the spinal nerves (roots of the cervical plexus).

10. Follow the internal jugular vein to its termination noting its tributaries. (Play movie; View images: N 8, 31, 33, 70, 74, 126, 256, TG 7-06, 7-11, 7-13, 7-15, 7-16, 7-51, 7-73, 7-75)

Trace the internal jugular vein caudally and identify superior thyroid and, if present, middle thyroid tributaries. At what foramen on the base of the skull does the internal jugular vein originate? Note its junction with the subclavian vein to form either the right or left brachiocephalic vein. Trace the external jugular vein until it joins the subclavian vein. Identify, trace (in the posterior triangle), and remove the transverse cervical and suprascapular veins. Note that the junction of subclavian and internal jugular vein is posterior to the sternoclavicular joint.

11. Look for deep cervical lymph nodes and find the thoracic duct on the left. (Play movie; View images: N 34, 36, 39, 72, 74, 193, 239, 266, 430, TG 4-18, 4-44, 5-37, 7-10, 7-14, 7-15, 7-17, 7-18, 7-74)

Observe lymph nodes along the internal jugular vein and veins of the posterior triangle (transverse cervical and suprascapular veins). The omohyoid muscle divides the deep cervical nodes into superior and inferior groups. These nodes form a chain and end in the jugular trunk, which drains the deep cervical nodes to the venous circulation at the junction of the internal jugular and subclavian veins (via the right lymphatic duct on the right side and the termination of the thoracic duct on the left). Note the arch and course of the thoracic duct as it emerges behind the esophagus in the upper thorax. The duct frequently looks like a vein due to blood backing up into it during the embalming process. However, identify it by its characteristic position, arching immediately deep to the internal jugular vein and lying upon the anterior scalene muscle. The right lymphatic duct is small and difficult to find.

Cervical lymph node groups

Identify the prevertebral fascia and locate the anterior scalene muscle. Remove the scalene fascia; expose and trace the phrenic nerve (C3-5) to its roots.

12. Dissect the root of the neck to expose the subclavian arteries and their branches, the cervical sympathetic trunk and its ganglia, and the recurrent laryngeal nerve. (Play movie; View images: N 32, 33A, 33B, 35, 75, 76, 130, 131, 135, 136, 177, 186, 191, 196, 232, 427, 477, TG 1-13, 2-09, 2-15, 4-09, 4-15, 4-20, 7-10, 7-14, 7-15A,7-15B, 7-17, 7-19, 7-95)

Carefully clean the connective tissue from the root of the neck, exposing the brachiocephalic, common carotid, and subclavian arteries. Expose both subclavian arteries throughout their length, defining parts and noting vagus, cardiac, and phrenic nerves as they cross anterior to the arteries. Pull the carotid sheath and its contents to one side and identify the prevertebral fascia. Locate the sympathetic trunk passing posterior and medial to the subclavian artery; you may find a loop of the trunk (ansa subclavia) around the artery. Follow the course of the trunk along the medial border of the common carotid artery or deep in the prevertebral fascia. Can you identify the middle cervical ganglion? Locate the recurrent laryngeal nerve (a branch of the vagus), which curves around the subclavian artery on the right side to ascend in the tracheo-esophageal groove.

Organize those parts of the cervical sympathetic trunk you have seen so far. Do you see connections (gray rami communicantes) between the trunk or ganglia and spinal nerves?

Recall the location and the cervical relationship of first rib and pleura (cupula) to the subclavian vessels. Taking care not to disrupt the thoracic duct, cut the junction of the subclavian and internal jugular veins. Pull these veins aside to identify branches of the subclavian artery: vertebral (trace it to the transverse foramen of the 6th cervical vertebra and note relation to sympathetic trunk and ganglia); thyrocervical trunk (note location and relation to phrenic nerve and anterior scalene muscle); transverse cervical and suprascapular arteries. Are these individual arteries or are they derived from a common trunk? Trace their course across the phrenic nerve and the anterior scalene muscle and through the posterior triangle to where they have been seen in previous dissections. Note the origin of the inferior thyroid artery and its course to the thyroid gland. Study its relation to the sympathetic trunk and middle cervical ganglion. Trace the internal thoracic artery. It arises from the subclavian opposite the thyrocervical trunk. It is crossed anteriorly by the phrenic nerve. Trace the dorsal scapular artery, a branch of the 3rd part of the subclavian. It may also be a branch of the transverse cervical artery. Trace it through the brachial plexus.

Vessels of the root of the neck

13. Cut the anterior scalene muscle to expose the costocervical trunk, the roots of the brachial plexus and nerves arising from them. (Play movie; View images: N 30, 33A, 33B, 185, 186, 429, 430, 477, TG 2-13, 2-14, 7-15A, 7-15B)

On the right side, carefully cut through the anterior scalene muscle, elevate the artery and look for the costocervical trunk. Define the interscalene triangle, identify middle and posterior scalene muscles. Trace the trunks and roots of the brachial plexus within the interscalene triangle and complete your organization of the brachial plexus. Dissect the following: suprascapular nerve, dorsal scapular nerve and long thoracic nerve (the last two of which penetrate the middle scalene muscle). Note that the brachial plexus passes superior and posterior to the subclavian artery in the interscalene triangle. In forced inspiration, what muscle raises the second rib?

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

On the left side, identify the retropharyngeal space and open it completely from the base of the skull to the root of the neck use blunt dissection to identify the cervical sympathetic trunk by elevating the carotid sheath structures and the neck viscera.

15. 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)?

16. Examine the subdivisions of the pharynx, noting their features. (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

17. Examine the cartilages and major subdivisions of the larynx. (Play movie; View images: N 15, 67, 77A, 77D, 78, 81A, 81E, TG 7-09, 7-19, 7-20, 7-23, 7-25, 7-26A, 7-27A, 7-28A)

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?

18. Dissect the larynx, its membranes, muscles, ligaments, vessels and nerves. (Play movie; View images: N 78, 82C, 82D, 83, 84A, 84B, 126, 235, TG 7-26B, 7-26C, 7-27B, 7-28B)

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.