Prelab Images - Carotid Sheath, Pharynx, & Larynx

Prelab should consist of reading the lab manual and dissector answers and viewing the dissection video. To begin your study, you may find it useful to look over the Netter's or LWW Atlas images listed below.

Step 1. Review the osteology of the pharynx, larynx and hyoid bone. (Play movie)

Plates N6, N8, TG7-06, TG7-08 show the foramen magnum, occipital condyles, hypoglossal canal, and jugular foramen (labeled as jugular fossa in plate N8, TG7-06). Plate N6, TG7-06 shows the external opening of the carotid canal. Plates N4, N8, TG7-06, TG7-32 label the styloid process. Plates N13, N77, TG7-09, TG7-25 show the hyoid bone and identify its body and greater and lesser horns. Plate N77, TG7-28 shows the thyroid, cricoid, and arytenoid cartilage.

Step 2. Open the retropharyngeal space and identify the cervical sympathetic trunk. (Play movie)

Plate N35, TG7-10 shows where the cervical sympathetic trunk is located in the retropharyngeal space. Plate N130, TG7-15 shows the cervical sympathetic trunk. On the right side, cut through the gray rami communicantes between the trunk and the ventral primary rami. On the left side, identify the sympathetic trunk but do not cut through the gray rami communicantes.

Step 3. On the right, disarticulate the atlanto-occipital joint. (Play movie)

In plate N34, TG7-17, begin your incision just behind the right ear, posterior enough to avoid the carotid sheath contents. Continue the incision to the posterior side of the body to the midline. Plate N21, TG1-09 shows the ligaments of the atlanto-occipital junction that must be cut. Then, insert a chisel between the atlas and the base of the skull on the right side and pry the head away from the body to give you more room. Now look at the cross-section in plate N35, TG7-10. You basically want to remove the trapezius, deep cervical muscles, scalene muscles, transverse process of the cervical vertebrae, and the longus colli muscle in order to see the buccopharyngeal fascia (outlined in plate N35, TG7-10). Try not to damage the carotid sheath contents or the sympathetic trunk. The back of the pharynx should look like plate N73, TG7-21, except with a lot of fascia and nervous tissue (pharyngeal plexus) covering its posterior aspect.

Step 4. Clean the cervical sympathetic trunk, vagus nerve, carotid arteries and internal jugular vein. (Play movie)

Plate N75, TG7-21 shows the back of the pharynx that you should now be able to see. Identify the vagus nerve (CN X) and internal jugular vein and follow them superiorly as they enter the skull through the jugular foramen (N8, TG7-06). The glossopharyngeal (CN IX) and accessory nerves (CN XI) also enter the skull through this foramen. Follow the internal carotid artery ( N75, TG7-21, TG7-72) superiorly until it enters the skull through the external opening of the carotid canal (N8, TG7-06). Plates N130, TG7-15, N131, TG7-21 identify the superior cervical ganglion and its branches to the pharyngeal plexus. As seen in TG7-95, TG7-21, the superior cervical sympathetic ganglion also gives off internal carotid nerve (which forms a plexus on the internal carotid artery) and the external carotid nerve (which forms a plexus on the external carotid artery). The two plexuses then follow the arteries to supply sympathetic innervation to the head ( N130, TG7-21, N131, TG7-15, TG7-95). The superior cervical sympathetic ganglion also sends off a superior cervical sympathetic cardiac nerve and the middle cervical ganglion sends off a middle cervical sympathetic cardiac nerve (plate N130, TG7-15, TG7-95). Plates N125, N130, and N131, TG7-14, TG7-92 show the vagus nerve. This nerve gives off branches to the pharyngeal plexus, the superior laryngeal nerve (seen with its internal and external branches in plates N75, N125, TG7-20, TG7-21, TG7-92), and superior and inferior cardiac branches. All of these branches are shown in plate N125, TG7-92. Plate N73, TG7-21 shows the back of the pharynx as you will see it, except there will be a venous plexus draining laterally into the internal jugular vein. Plate N130, TG7-71, TG7-90 shows the carotid bifurcation, carotid sinus, the carotid body, and the internal carotid artery. Plate N130, TG7-71 shows the ascending pharyngeal artery branching off the external carotid artery near the superior thyroid artery and moving superiorly along the posterior side of the pharynx. Plate N73 labels the retropharyngeal lymph nodes.

Step 5. Identify and trace the glossopharyngeal, accessory, and hypoglossal nerves. (Play movie)

Plate N125, TG7-90 shows the glossopharyngeal nerve (CN IX) sending out a branch to the stylopharyngeus muscle (muscle best seen in plate N67, TG7-20), its sensory pharyngeal branch, and its branch to the carotid sinus. Remember, the vagus supplies motor to the rest of the muscles of the pharynx besides stylopharyngeus. Plate N71, TG7-21 also shows CN IX. The accessory nerve (CN XI) was probably identified in an earlier dissection as it innervated the sternocleidomastoid muscle (plate N32, TG7-17, TG7-18, TG7-93). Plate N71, TG7-18 shows how far posterior this nerve will be found in the superior neck (posterior to the internal jugular vein). Plate N127, TG7-93 highlights CN XI. The hypoglossal nerve is perhaps easiest to find in the submandibular triangle just before passing deep to the mylohyoid muscle (plate N32, TG7-17, TG7-94). Plate N71, TG7-18 shows it in the superior neck. Plate N128, TG7-94 highlights CN XII.

Step 6. Clean and identify the muscles of the pharynx and pharyngeal plexus. (Play movie)

The pharyngeal plexus of nerves is composed of sympathetic fibers from the superior cervical ganglion ( N130, TG7-21, N131), parasympathetic and motor fibers from the vagus nerve (N126, TG7-92, N130, TG7-21, and N131), and sensory fibers from the glossopharyngeal nerve (plate N125, TG7-90). Plate N35, TG7-10 labels the buccopharyngeal fascia, which must be removed from the back of the pharynx along with the pharyngeal plexus of veins. Plates N68, TG7-25, N13, TG7-09 label the greater horn of the hyoid bone and plates N68, TG7-26, N77, TG7-25 label the superior horn of the thyroid cartilage. The pharyngeal constrictor muscles (superior, middle, and inferior) and the pharyngobasilar fascia are labeled in plate N67, TG7-21. The stylopharyngeus muscle (remember this one receives motor innervation from the glossopharyngeal nerve) is also shown in plate N67, TG7-21 passing between the superior and middle pharyngeal constrictor muscles.

Step 7. Examine the pharyngeal and laryngeal cavities, noting their regions and prominences. (Play movie)

Plate N67, TG7-23 identifies the nasal, oral, and laryngeal portions of the pharynx. The nasal septum, soft palate, and the base (root) of the tongue are identified in plate N67, TG7-22. Plates N67, TG7-23, N70, TG7-22 identify the epiglottis. The choanae are identified in plates N41, TG7-41, N70, TG7-22. The uvula can be seen in plates N64, TG7-23, N66, TG7-22. Plate N62, TG7-39 shows median and lateral glossoepiglottic folds. The piriform recess is labeled in plate N70, TG7-22. The entrance to the esophagus can be seen in plates N67, TG7-23, N69, but the entrance is not labeled.

Step 8. Dissect the larynx, its membranes, muscles, ligaments, vessels and nerves. (Play movie)

Plate N81, TG7-25, TG7-26, and TG7-28 identify the cartilages of the larynx (thyroid, cricoid, arytenoids) and the features of the hyoid bone (also see plate N15, TG7-09 for the hyoid bone). Plate N83 (top) shows the cricoarytenoid joint and the hinge like motion produced at this joint. Plates N67, TG7-26, N81, TG7-27 identify the epiglottis. Plates N70, TG7-22, N82, TG7-28 identify the aryepiglottic folds. The interarytenoid notch is labeled in plate N70, TG7-22. Plate N70, TG7-22 also labels the laryngeal inlet (aditus). The piriform recess is labeled in plate N70, TG7-22. The arytenoid cartilage and lamina of the cricoid cartilage is identified in plate N81, TG7-28. The muscles that produce movement and the cricoarytenoid joint are considered in plate N83, TG7-27, TG7-28. The vestibule, ventricle, rima glottidis, infraglottis, and glottis are all not labeled in Netter's atlas. They will be explained shortly. Looking at plate N70, TG7-22, strip away the mucosa of the anterior part of the laryngopharynx. The internal branch of the superior laryngeal nerve can be found traveling in the piriform recess (N70, TG7-22). Plates N80, N84, TG7-26 show the path of the recurrent laryngeal nerve. This nerve changes its name to the inferior laryngeal nerve (N84, TG7-26) and innervates all the muscles of the larynx except for the cricothyroid muscle (this muscle is innervated by the external branch of the superior laryngeal nerve). The inferior laryngeal artery, a branch off of the inferior thyroid artery, travels with the inferior laryngeal nerve (N80, TG7-26). Plate N82, TG7-28 identifies the posterior cricoarytenoid and arytenoideus muscles. Plate N82, TG7-27 identifies the conus elasticus and the vocal ligament. The vocal process of the arytenoid cartilage is labeled in plate N81, TG7-27. The true vocal fold is labeled in plate N67, TG7-23. The quadrangular membrane and vestibular fold are shown in TG7-22. Plate N67, TG7-23 show the false and true vocal folds. The area of the larynx above the false vocal (vestibular) folds is known as the vestibule. The submucosa lining the vestibule is called the quadrangular membrane. The lower edge of the quadrangular membrane is covered by mucosa to form the false vocal fold. Similarly, the conus elasticus (N82, TG7-27) lines the inferior part of the larynx as submucosa. The upper edge of the conus elasticus thickens to form the vocal ligament. The vocal ligament and accompanying muscles are covered by mucosa to form the true vocal fold (N67, TG7-23). The area inferior to the true vocal fold and superior to the trachea is the infraglottis. The lateral space that exists between the false and true vocal folds is called the ventricle. Looking at plate N82, TG7-27 the glottis is defined as the vocal folds plus the space in between them and the rima glottidis is just the space between the vocal folds. See objective 9 and question 18 of the dissector answers for more information on the structure of the larynx.

Plates N74, N77, TG7-25 label the thyrohyoid membrane. Plates N74, N76, TG7-26B and TG7-26C show the internal branch of the superior laryngeal nerve and the superior laryngeal artery piercing the thyrohyoid membrane. Plate N126, TG7-20 shows the vagus nerve (CN X), which is source of the superior laryngeal nerve. Plate N69, TG7-19 shows the external carotid artery giving off the superior thyroid artery, which then gives off the superior laryngeal artery. Plates N67, TG7-22, N233 label the piriform recess and plate N235, TG7-28 shows the superior laryngeal artery and internal branch of the superior laryngeal nerve running in this recess (you will have to cut through the thyrohyoid membrane or open up the pharynx in order to see this). Once again, plate N78, TG7-26 shows the cricothyroid muscle and plates N74, N75, TG7-20, and N76 show the external branch of the superior laryngeal nerve innervating the inferior pharyngeal constrictor muscle before innervating the cricothyroid muscle. Plates N75, TG7-20, N76, and N126, TG7-21 trace the internal and external branches back to the superior laryngeal nerve of the vagus. Finally, plate N78, TG7-27 labels the conus elasticus and plate N77, TG7-26 (right lateral view) shows its median cricothyroid ligament.