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:

• are a continuation of the thoracic sympathetic trunks
• lie behind and medial to the carotid sheath and in front of prevertebral muscles
• may be a solid trunk or strands connecting 2 or 3 cervical ganglia
• cervical ganglia represent consolidation of the original 1 ganglion per cervical spinal nerve, which is the pattern in the thorax. This consolidation of ganglia happens in areas where there are gray rami but no white rami, such as above T1 or below L2.
• there are only gray rami communicantes between the cervical trunk and spinal nerves C1-C8, because the highest level for white rami is T1. This means that all of the preganglionic fibers of the cervical sympathetic trunk originated at T1 or below (generally T1-T5). Postganglionic fibers in the cervical sympathetic trunk originate from one of the three cervical ganglia (or thoracic ganglia).
• much of the sympathetic innervation of the deep structures of the head occurs via perivascular sympathetic nerve plexuses that follow branches of the external and internal carotid arteries.

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:

• external carotid nerve reaches external carotid artery to form the external carotid plexus. These perivascular fibers follow branches of the external carotid to all the structures it supplies. For example, parotid gland sympathetic innervation comes via the perivascular external carotid plexus (vasoconstriction reduces salivation).
• internal carotid nerve, forming the perivascular internal carotid plexus to the brain, orbit, and forehead.
• branches to the carotid body.
• superior cervical cardiac nerve (accelerates heart rate and increases force of contraction).
• sympathetic contributions to glossopharyngeal (CN IX), vagus (CN X), and hypoglossal (CN XII) nerves.
• branches to join the pharyngeal plexus (along with glossopharyngeal and vagus).

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:

• middle cervical cardiac nerve, which has cardioaccelerator fibers, visceral afferent fibers to the heart, and fibers that go to the thyroid.

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:

• inferior cervical cardiac n.
• perivascular fibers to vertebral a. and from there into the brain, onto basilar, posterior cerebral, and cerebellar aa.
• the ansa subclavia is a superficial strand that loops down from the middle cervical ganglion anteriorly around the subclavian artery and joins the inferior cervical ganglion behind the artery.
• this ganglion also receives a white ramus from T1.

Functions of the cervical sympathetic trunk:

• recall that sympathetic nerves cause vasoconstriction, secretion (sweat glands), pilomotor functions, and contraction of smooth muscle. Vasoconstriction can reduce output of glands like parotid by reducing blood flowing in. Specifically, the cervical sympathetic trunk controls:
• vasoconstriction of all the blood vessels of the brain and head (perivascular fibers)
• blood vessels to salivary glands and other oral glands (external carotid n.)
• acceleration of heart rate and strength of cardiac contraction through superior, middle, and inferior cervical cardiac nerves
• innervation of hair muscles and sweat glands on the head
• innervation of dilatator pupillae m. of the eye and superior tarsal m. of the eyelid. (Think about the eyes going wide with fright, a sympathetic-stimulating emotion.)

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)

I	Olfactory	Some	Sensory
II	Optic	Say	Sensory
III	Oculomotor	Money	Motor
IV	Trochlear	Matters	Motor
V	Trigeminal	But	Both
VI	Abducens	My	Motor
VII	Facial	Brother	Both
VIII	Vestibulocochlear	Says	Sensory
IX	Glossopharyngeal	Big	Both
X	Vagus	Brains	Both
XI	Accessory	Matter	Motor
XII	Hypoglossal	Most	Motor

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:

• nasopharynx, most superior, is behind the nasal cavity and superior to the soft palate. It is strictly respiratory. Air enters the nasopharynx through the posterior openings of the choanae, which are bisected by the posterior edge of the nasal septum. At the upper posterior end of the nasopharynx is the pharyngeal tonsil, which is lymphoid tissue known as adenoids when enlarged. The auditory tube to the middle ear opens into the lateral wall of the nasopharynx. Its opening is covered by the torus tubarius. The salpingopharyngeal fold is a vertical fold of mucous membrane extending inferiorly from the opening of the auditory tube.
• oropharynx, the middle portion of the pharynx, is posterior to the oral cavity and connects with the nasopharynx above and the laryngopharynx below. The dorsum of the tongue is anterior to the oropharynx. The inferior border of the oropharynx is the epiglottis. Anteriorly it is continuous with the oral cavity at the palatopharyngeal folds or arches.
• laryngopharynx, the most inferior part of the pharynx, lies below the oropharynx and posterior to the larynx. It extends from the epiglottis superiorly down to the inferior border of the cricoid at C6. Its posterior and lateral walls are formed by the middle and inferior pharyngeal constrictor muscles. Internally, the walls are formed by palatopharyngeus and stylopharyngeus muscles. The laryngeal inlet connects the laryngopharynx with the larynx. (Aside: Lateral to the laryngeal inlet are the piriform recesses, where foreign bodies can become lodged.) The laryngopharynx is continuous inferiorly with the esophagus.

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:

Motor:
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).

Sensory:
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)

• Bolus begins to move from the mouth into oropharynx by action of muscles of tongue and soft palate. (voluntary)
• The soft palate is elevated by the levator veli palatini and (to a lesser extent) tensor veli palatini muscles to seal off the nasopharynx. (actions are involuntary from here down)
• The salpingopharyngeus muscle (one of the internal longitudinal pharyngeal muscles) contracts drawing the lateral pharyngeal walls upward.
• As the bolus moves into the back of the pharynx, the palatopharyngeus and stylopharyngeus mm. (the other 2 longitudinal muscles) elevate the larynx and pharynx causing the cavity to widen to receive the bolus.
• After food passes the epiglottis, the superior, middle, and inferior pharyngeal constrictors - all circular muscles - contract, one after the other, to push the bolus into the esophagus.

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.

• The inlet and vestibule of the larynx are above the vestibular (false vocal) folds. The epiglottis, arytenoid cartilages, cuneiform and corniculate cartilages, aryepiglottic folds, and piriform recesses are components here. Just below the inlet is the widening called the vestibule, which ends below at the rima vestibuli, the aperture between the false vocal folds. The lateral walls of the vestibule are formed by the quadrangular membranes. The free inferior margins of the quadrangular membranes form the vestibular folds (or false vocal folds). The rima vestibuli, the opening between the vestibular folds, is wider than the rima glottidis or glottis, the space between the true vocal folds, below.
• The ventricle of the larynx is a cavity just below the vestibular folds and just superior to the true vocal folds. The ventricle functions as a resonance chamber.
• The infraglottic cavity extends from the glottis - the space between the vocal folds - to the beginning of the trachea below. The true vocal folds, at the superior end of the infraglottic cavity, are two mucous-membrane-covered vocal ligaments stretched between the vocal processes of arytenoids and the deep surface of the anterior angle of the thyroid cartilage. Vocalis and thyroarytenoid muscles lie lateral, parallel, and adjacent to the vocal ligaments. These are the parts of the larynx directly involved in making sound.

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):

• Thyroid cartilage - largest, unpaired. Extends laterally but is not continuous posteriorly, so it doesn't form a complete ring around the airway. Is composed of two quadrilateral laminae fused together in the anterior midline where there is a dip called the superior thyroid notch. This dip projects anteriorly to form the laryngeal prominence (Adam's apple). Along the lateral margins of the cartilage are the oblique lines running from the superior to inferior tubercles. The oblique line provides a point of attachment for the sternothyroid and thyrohyoid muscles anteriorly and the inferior pharyngeal constrictor muscle posteriorly. The superior border of the thyroid cartilage attaches to the hyoid bone by the thyrohyoid membrane. Inferior horns of the thyroid cartilage articulate with the lateral surface of the cricoid at the cricothyroid joints. The interior of the thyroid cartilage is covered by the mucous membrane of the interior of the larynx. The interior part of the thyroid cartilage deep to the superior notch is the point of attachment for the stem of the epiglottis, the vocal and vestibular ligaments, and three muscles: thyroarytenoid and its thyroepiglottic and vocalis parts.
• Cricoid cartilage - is an unpaired signet-ring-shaped cartilage with the narrow band (the arch) facing anteriorly and the broadened signet portion (the lamina) facing posteriorly. The cricoid is the only complete ring of cartilage to encircle the airway. Cricoid attaches to the thyroid cartilage by the median cricothyroid ligament and to the trachea below by the cricotracheal ligament. The cricothyroid muscle attaches to the anterior and lateral borders of the cricoid cartilage, and the inferior pharyngeal constrictor attaches to its posterior border. The posterior superior aspect of the cricoid is notched, and on either side of the notch are smooth surfaces for articulation with the bases of the 2 arytenoid cartilages. The inner surface of the cricoid is lined with mucous membrane.
• Arytenoid cartilages - paired, three-sided, pyramid-shaped bodies that lie on the superior margin of the cricoid lamina. The anterior protrusion of the pyramid is the vocal process which is connected to the vocal ligament. The muscular process protrudes laterally, to which are attached the posterior and lateral cricoarytenoid muscles. (Stretching between the posterior surfaces of the two arytenoids are the transverse and oblique arytenoid muscles. Attached to the anterolateral surface of the arytenoid are the thyroarytenoid muscle with its vocalis and thyroepiglottic parts.)
• Corniculate cartilages - paired, small cartilages that sit on top of the apices of the arytenoids.
• Cuneiform cartilages - paired, rod shaped bodies in the aryepiglottic fold lateral to the epiglottis.
• Epiglottic cartilage - an unpaired, spoon-shaped cartilage which is attached (by the thyroepiglottic ligament) at its inferior tapered end (tubercle of the epiglottis) to the superior thyroid notch. The superior end is free and curved anteriorly, while the anterior surface is attached to the hyoid bone by the hyoepiglottic ligament. It is covered by mucosa. The posterior surface of the epiglottis faces the vestibule of the larynx. It is pitted to accommodate small mucous glands.

Membranes of the larynx:

• Thyrohyoid membrane - suspends the thyroid cartilage and thus the larynx from the hyoid bone above. The median portion of this membrane is thickened, forming the median thyrohyoid ligament. Lateral thyrohyoid ligament on the sides of the larynx extends between the superior horn of the thyroid cartilage and to the end of the greater horn of the hyoid bone.
• Quadrangular membrane - above the vocal ligament is a thin sheet of connective tissue connecting the lateral part of the epiglottic cartilage with the arytenoid. Its lower free margin, above the vocal ligament, is the vestibular ligament of the false vocal (vestibular) folds.
• Conus elasticus - is an elastic membrane hanging down like a sheet from the vocal ligament above to the cricoid cartilage below. The lower attachment of this sheet stretches in a semicircle from the base of one arytenoid to the other. The thickened superior margins of the conus - the vocal ligaments - attach the vocal processes of the arytenoids to the inner surface of the laryngeal prominence, below the superior thyroid notch. This forms the V shape of the abducted vocal ligaments when seen from above.
• Hyoepiglottic and thyroepiglottic ligaments - attach the epiglottis to the hyoid bone and thyroid cartilage anteriorly.
• Cricotracheal ligament - connects the inferior border of the cricoid to the first ring of the trachea.

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)

• Cricothyroid muscles (paired) - On the external surface of the larynx. Arise from the anterior arch of the cricoid cartilage and fibers travel backward and upward to insert into the inferior border of the thyroid cartilage. Action: pulls the thyroid cartilage down and toward the cricoid. Result: increases the distance between the arytenoids and the thyroid cartilage, tensing the vocal folds. Helps control pitch.
• Posterior cricoarytenoid muscles (paired) - Lie on the dorsal surface of the cricoid cartilage. Fibers originate near the posterior midpoint, and run laterally from there in both directions to attach to the back of the muscular processes of the arytenoid cartilages. Action: when muscles contract, they pull the muscular processes posteriorly and the vocal processes laterally. Result: Abduction of the vocal folds. These are the only abductors of the vocal folds. Without them, the vocal folds adduct permanently, and you suffocate.
• Lateral cricoarytenoid muscles (paired) - Originate from the upper anterior border of the cricoid cartilage. Fibers pass posteriorly left and right and insert on the anterior aspect of the muscular processes of the arytenoid cartilages. Action: Upon contraction, muscular processes are pulled anteriorly and vocal processes are pulled medially. Result: Adduction of the vocal folds.
• Arytenoid muscles (two, but unpaired) - These muscles, oblique and transverse, attach the posterior surfaces of the arytenoids to one another. Oblique fibers are continuous with the aryepiglottic muscles, which help to pull epiglottis down toward the larynx during swallowing. Action: Upon contraction, pulls the arytenoids medially (toward each other). Result: Adduction of the vocal folds.
• Thyroarytenoid muscles (paired) - Border the vocal ligaments. Arise from the anterior inner surfaces of the thyroid laminae, deep to the laryngeal prominence, and insert on the lateral borders of the arytenoid cartilages. Action: they pull the arytenoid cartilages closer to the thyroid cartilages, Result: reduced tension of the vocal ligament. In the process of shortening, these muscles also thicken and this helps seal the glottis. Thus they are considered sphincters of the glottis.
• Vocalis muscles (paired) - are composed of the fibers of thyroarytenoid muscles closest to the vocal ligaments. Each vocalis attaches to the elastic tissue of the vocal ligament. Action: Contraction affects frequency of vibration of the vocal ligaments. Result: Control of pitch and the fine adjustments required in vocalization.

9. Describe the innervation and vascular supply of the larynx. (N 76, 80, TG 7-26B, 7-26C, 7-28)

Innervation:

• Vagus, through superior laryngeal and inferior laryngeal nerves, innervates the entire larynx.
  • Superior laryngeal, internal branch: the principal sensory nerve of the larynx, sending fibers from the supraglottic portion of the larynx; also sends parasympathetic fibers to the mucous glands of the interior of the supraglottic portion of the larynx.
  • Superior laryngeal, external branch: only innervates the cricothyroid muscle.
  • Inferior laryngeal: Is the continuation of the left and right recurrent laryngeal nerves. It innervates all intrinsic muscles of the larynx except cricothyroid.

Vascular supply:

• Superior laryngeal artery, branch of the superior thyroid artery, pierces the thyrohyoid membrane along with the internal branch of the superior laryngeal nerve.
• Inferior laryngeal artery, branch of the inferior thyroid artery, passes under the inferior pharyngeal constrictor muscle along with the inferior laryngeal nerve.

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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)