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

Learning Objectives and Explanations:

1. Review the arrangement, distribution and function of the cervical sympathetic trunk. (WB 211-12; N 35, 128, 130, 131, 209, TG 7-10, 7-15, 7-95)
The left and right cervical sympathetic trunks: The superior cervical ganglion sends gray rami to C1-C4 spinal nerves (variable) and also gives off other branches. It lies opposite the transverse process of C2. Besides the gray rami to the spinal nerves, branches of the ganglion include: The middle cervical ganglion (which may be absent) sends gray rami to C5-6 spinal nerves. It is at the level of the cricoid cartilage, often close to where the inferior thyroid artery crosses the sympathetic trunk. Besides the gray rami, branches include: The cervicothoracic or stellate ganglion, the fusion of the inferior cervical and first thoracic ganglia, sends gray rami to C6,7,8 and T1. It lies anterior to the transverse process of C7 or the head of rib 1. Its other name, stellate ganglion, comes from the fact that its multiple branches spread out like light rays from a star. Branches include: Functions of the cervical sympathetic trunk: Horner's syndrome involves a lesion of the sympathetic trunk. Two of the more noticeable signs of this syndrome are constriction of the pupil and slight ptosis (drooping) of the eyelid.
2. Review the carotid sheath and contents. (WB 201,203,206; N 32, 33, 35, 125, 126, TG 7-17, 7-18, 7-13, 7-10)
The carotid sheath is a tube-shaped fascia wrapping the common carotid a., internal carotid a., internal jugular v., and vagus n. It lies anterolateral to the cervical sympathetic trunk, behind the sternocleidomastoid muscle. The sheath blends with the thyroid fascia anteromedially and with the deep surface of sternocleidomastoid anterolaterally. Posteriorly it is attached to prevertebral fascia along the tips of the transverse processes of vertebrae. It ends at the base of the skull where it attaches around the jugular foramen and carotid canal. It is here at the base of the skull that the internal carotid artery and internal jugular vein go their separate ways. Inferiorly, the carotid sheath fuses with scalene fascia, adventitia of great vessels, and the fibrous pericardium.

Within the sheath, artery is medial, vein lateral, and nerve posterior and between the vessels.

The superior root of ansa cervicalis (from cervical plexus C1-2) lies draped over the anterior part of the carotid sheath.

The carotid sinus is the dilated terminal part of the common carotid artery, approx. 1 cm long. It is a baroreceptor in the elastic wall which responds to changes in blood pressure. The carotid sinus is innervated by a branch of the glossopharyngeal nerve.

The carotid body is an disc-shaped mass lying behind the bifurcation of the common carotid artery. It has a chemoreceptor sensitive to blood oxygen concentration. The carotid body is innervated by the nerve to carotid sinus from glossopharyngeal nerve, and also receives the nerve to carotid body, a branch of the vagus n. (CN X), as well as sympathetic fibers.
3. Identify, trace and describe the general functions of cranial nerves IX (glossopharyngeal), X (vagus), XI (spinal accessory), XII (hypoglossal). (WB 91,205,206,218,239; N 118, N125, 127, 128, TG 7-90, 7-91, 7-93, 7-94)

Glossopharyngeal, CN IX, Both motor and sensory.
Emerges from medulla in the groove dorsal/lateral to the olive, passes through jugular foramen, passes along the posterior border of stylopharyngeus m.

The short story:
  • Motor: innvervates stylopharyngeus m. (that's the only muscle it innervates)
  • Sensory: posterior 1/3 of tongue: general sensory (pain, etc) and special sensory (taste); sensory to pharynx via pharyngeal plexus
The long story . . . Branches include:
  • Tympanic n. - parasympathetic fibers to otic ganglion, which supplies parotid gland (increases salivation) and mucous membrane of the middle ear
  • Carotid sinus nerve, with branches to carotid sinus and carotid body
  • Pharyngeal branches which form the pharyngeal plexus (along with vagus and cervical sympathetics)
  • Branches to stylopharyngeus (the ONLY motor branches of this nerve)
  • Branches to tonsils
  • Lingual branches - afferent fibers from the tongue report taste sensations and somatic sensations from the posterior third of the tongue
Vagus, X, Both motor and sensory.
Arises from the medulla, in the groove dorsal and lateral to the olive, in the same plane as glossopharyngeal (CN IX) and accessory (CN XI). The vagus leaves the skull through the jugular foramen, descends through the neck in the carotid sheath behind and between the internal carotid/common carotid and the internal jugular v.

The short story:
  • Vagus supplies all the muscles of the pharynx and soft palate and upper 2/3rds of esophagus EXCEPT stylopharyngeus (from glossopharyngeal) and tensor veli palatini (from mandibular division of trigeminal V3). It does this primarily through the pharyngeal plexus. The inferior pharyngeal constrictor is innervated by the superior laryngeal external branch.
  • Vagus, through the superior and inferior laryngeal nerves, also supplies all muscles and sensory innervation of the larynx.
  • Motor: The inferior laryngeals (=recurrent laryngeals) supply all the muscles of the larynx EXCEPT cricothyroideus. Superior laryngeal external branch supplies cricothyroideus.
  • Sensory: The inferior laryngeals supply sensory fibers to the larynx below the vocal folds, but their role is minor in sensation. Superior laryngeal internal branch supplies sensory fibers to the larynx above the vocal folds. It is the principal sensory nerve of the larynx, according to W+B.
  • It also supplies fibers to the dura, trachea, heart, etc
The long story...
Branches include:
  • meningeal to posterior dura mater
  • auricular to back of external ear
  • pharyngeal, which contribute to the pharyngeal plexus. The pharyngeal plexus (from vagus, glossopharyngeal, and cervical symp trunk) supplies the constrictor muscles
  • superior laryngeal n. Arises from the inferior ganglion of the vagus. Passes inferomedially toward the larynx. Has 2 branches.
    • internal branch: sensory to the mucous membrane of epiglottis
    • external branch: inferior pharyngeal constrictor m., cricothyroid m.
  • cervical cardiac
  • recurrent laryngeal
    • right recurrent laryngeal loops under and behind the subclavian a.
    • left recurrent laryngeal loops under aortic arch
    • both recurrent laryngeals ascend between the esophagus and trachea and enter the larynx from under the inferior constrictor muscle. Above the cricothyroid articulation, name changes to inferior laryngeal n.
    • branches of the laryngeals include: cardiac, tracheal, esophageal, pharyngeal branch to inferior pharyngeal constrictor m.
    • inferior laryngeals innervate all intrinsic muscles of the larynx EXCEPT cricothyroideus
Accessory, CN XI, Motor nerve.
Arises from rootlets of C1-C5 which ascend within the vertebral column through foramen magnum. It then descends through the jugular foramen, where it receives fibers from the cranial portion of the accessory nerve. Upon leaving through the jugular foramen, the accessory nerve lies between the internal carotid and internal jugular veins. It travels laterally, piercing and innervating sternocleidomastoid. It then passes through the muscle, goes dorsally under the superficial layer of deep cervical fascia to trapezius, where it joins sensory branches of C3 and C4 to form the subtrapezial plexus.
Hypoglossal, CN XII, Motor nerve.
Motor nerve of the tongue arises from the medulla oblongata in the anterolateral sulcus between the pyramid and the olive. The rootlets which form the hypoglossal unite in the hypoglossal canal. It emerges from the canal medial to carotid sheath, then goes lateral. Travels for a short distance with the superior root of ansa cervicalis. Turns forward near angle of the mandible, loops around occipital artery, enters the submandibular triangle deep to posterior belly of digastric, and goes superior to the greater horn of the hyoid bone. Terminal branches distribute to styloglossus, hyoglossus, genioglossus, and intrinsic muscles of the tongue. Carries C1 and C2 fibers that leave as the superior root of ansa cervicalis, and the nerves to the thyrohyoid and geniohyoid muscles.
4. Describe the pharynx, its anatomical architecture and action of its musculature during swallowing. (WB 235; N 35, 63, 65, 66, 67, N125, 126, 130, TG 7-10A, 7-10B, 7-20, 7-21, 7-22, 7-24)
The pharynx is the multi-purpose chamber that connects the nasal and oral cavities superiorly with the esophagus and larynx inferiorly. It is multi-purpose in that it is the common pipe for food, liquids, and air, and it is the job of the pharynx to see that these invaluable items travel through the right pipe to the proper destination.

The pharynx is the part of the digestive system posterior to the nasal and oral cavities, extending posteriorly and inferiorly past the larynx. It extends to the inferior border of the cricoid anteriorly and the inferior border of C6 posteriorly. The posterior wall of the pharynx lies against the prevertebral layer of deep cervical fascia.

In the pharynx the paths of food and air cross. Food travels from the mouth (anterior) to the esophagus (posterior). Air travels from the choanae (posterior) to the trachea (anterior).

The interior of the pharynx is divided into 3 parts: Structure of the pharynx:
The wall of the pharynx is composed of two layers of 3 muscles each. The external rings of circular constrictor muscles - the superior, middle, and inferior constrictors - contract serially to push a bolus down to the esophagus. The internal ring of longitudinal muscles - palatopharyngeus, stylopharyngeus, and salpingopharyngeus - elevate and widen the pharynx to accommodate a bolus during swallowing. The fascia covering the outside of the posterior of the pharynx is the buccopharyngeal fascia. The interior fascia is the pharyngobasilar fascia.
Innervation of the pharynx:
Pharynx muscles are innervated by branches from pharyngeal plexus with 2 exceptions: stylopharyngeus (glossopharyngeal, CN IX) and tensor veli palatini (supplied by mandibular division of trigeminal, V3). Other than these two exceptions, the vagus is the source of motor innervation to the pharynx. The inferior pharyngeal constrictor also receives innervation from the recurrent laryngeal and external branch of the superior laryngeal (which are also derived from the vagus).

The glossopharyngeal sensory contribution to the pharyngeal plexus is connected to the mucosa of all three parts of the pharynx. (Sensory nerve supply to the nasopharynx is primarily from the maxillary division of trigeminal, V2)
The stages of swallowing (deglutition) (W+B 238)
5. List the basic functions of the larynx.
The larynx connects the superior pharynx (oro- and naso-) with the trachea. It is specialized for producing voice, and a special part of the larynx - the epiglottis - protects the airway during swallowing. To achieve these added functions, the larynx has additional cartilages, muscles, ligaments, and mucous membranes.
6. Describe the anatomy of the interior of the larynx. (N 65, 66, 77, TG 7-22, 7-24, 7-27)
The laryngeal cavity extends superiorly from the laryngeal inlet at the border with the laryngopharynx to the inferior border of the cricoid. It is covered with a mucous membrane, which is continuous with the pharynx above and trachea below. It has three parts.
7. Identify the main cartilages and membranes that form the internal framework (skeleton) of the larynx. (N 78A, 78B, 78C, 78D, 78E, TG 7-25, 7-28, 7-26, 7-27)
The larynx has nine cartilages (three unpaired and three paired): Membranes of the larynx:
8. Describe the actions of the intrinsic muscles of the larynx in tensing, relaxing, abducting or adducting the vocal folds. (N 78C, 78D, 79, TG 7-26, 7-27, 7-28)
9. Describe the innervation and vascular supply of the larynx. (N 76, 80, TG 7-26B, 7-26C, 7-28)
Innervation: Vascular supply:

Questions and Answers:

10. Identify the ascending pharyngeal artery (a branch of the external carotid) distributing to the dorsal wall of the pharynx. Do you find any lymph nodes (retropharyngeal)?
Retropharyngeal lymph nodes are usually present in the tissue between visceral and musculoskeletal parts of the neck, known as the retropharyngeal space, but difficult to find unless they are enlarged by disease. They are associated with the deep cervical nodes found in the carotid sheath just lateral to the space. (N 73, 136, TG 7-74)
11. Observe the pharyngobasilar fascia forming the pharyngeal wall above the superior pharyngeal constrictor. What tissue is it?
The wall of digestive and respiratory tracts, of which the pharynx is common to both, consists of a mucosal lining, a connective tissue layer - the submucosa - and a muscular wall. The pharyngobasilar fascia is the submucosa of the pharyngeal wall. (N 67, TG 7-21)
12. Clear the stylopharyngeus muscle and trace to the pharynx. Between what two muscles does it pass?
The stylopharyngeus muscle passes between the superior and middle pharyngeal constrictors. (N 67, TG 7-21)
13. Consider the complete blood supply to pharyngeal constrictors. Innervation?
The pharynx is supplied by the ascending pharyngeal artery, branches of the facial, maxillary and inferior thyroid. The pharynx receives nerves from the pharyngeal plexus which is composed of branches of the glossopharyngeal nerve (sensory), the vagus (motor and parasympathetic motor to the glands of the mucosa) and the sympathetic trunk (vasomotor to the blood vessels of the pharynx). (N 69, 75, 125, 126, 130, 131, 136, TG 7-22, 7-21, 7-20, 7-23, 7-24)
14. Define nasal, oral and laryngeal portions of pharynx. What boundaries separate these regions?
The nasopharynx extends from the choanae anteriorly to the soft palate inferiorly; it is the respiratory portion of the pharynx. The oropharynx extends from the soft palate above to the epiglottis below and opens into the mouth anteriorly. The laryngopharynx extends from the epiglottis to the beginning of the esophagus below. It opens into the larynx anteriorly.
14a. What structures lie immediately deep (lateral) to the palatine tonsil? Where is the lingual tonsil?
The superior pharyngeal constrictor muscle lies lateral to the palatine tonsil, along with the vessels supplying the tonsil. The lingual tonsil is in the submucosa on the superior surface of the root of the tongue just behind the sulcus terminalis. It is a large collection of lymphoid nodules that give the posterior one-third of the tongue its warty appearance.
15. 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?
The thyroid cartilage in male and female are different in shape. In the female, the two thyroid laminae meet in an angle of about 120 degrees. In the male, the thyroid laminae meet at an angle of 90 degrees. Thus the laryngeal prominence (the so called "Adam's apple") in the male is more obvious. The shape as well determines the length of the vocal cords and their consequent pitch; the cords being shorter in women and thus a higher pitched voice.
16. What is the action of the cricothyroid joint?
The cricothyroid muscle brings the arch of the cricoid and the thyroid cartilage together with the pivot at this joint. During this action the vocal folds become more tense and the pitch of the voice increases. Conversely paralysis of this muscle produces hoarseness of voice.
17. What is the glottis?
The glottis is defined as the space between the true vocal folds. It is also called the rima glottidis to differentiate it from the rima vestibuli, the space between the vestibular or false vocal folds.
18. What is the source of the inferior laryngeal nerve and the inferior laryngeal artery?
The inferior laryngeal nerve is the terminal end of the recurrent laryngeal nerve. It is motor to the intrinsic muscles of the larynx, while the recurrent laryngeal supplies the trachea and esophagus as well. The inferior laryngeal artery is a branch of the inferior thyroid artery; it accompanies the nerve into the space deep to the piriform recess.
19. Identify two structures that perforate the thyrohyoid membrane: the internal branch of the superior laryngeal nerve and the superior laryngeal artery. What is the source of each?
The internal branch of the superior laryngeal nerve is a sensory nerve to the interior of the larynx which arises from the vagus. The superior laryngeal artery and vein arise as the first branches of the superior thyroid vessels. (N 69, 74, 126, TG 7-26, 7-28)
20. Does the external branch of the superior laryngeal nerve pass through or give off a branch to the inferior pharyngeal constrictor muscle?
The external branch of the superior laryngeal nerve usually passes through the lower portion of the inferior constrictor muscle (this portion a.k.a. cricopharyngeus m.) supplying it and the cricothryroid muscle. (N 74, 75, 76, TG 7-20, 7-26)