S3 Larynx and Pharynx - Learning Objectives

1. Describe the boundaries, muscles, fascia, vasculature, and innervation of the pharynx, and the boundaries of the retropharyngeal space.

BOUNDARIES:

The pharynx is a common space for the conductive pathways of the respiratory (gases) and digestive (food and drink) systems. As such, the pharynx shares borders with the nasal cavity (choanae), oral cavity (faucial isthmus), larynx (laryngeal inlet), and esophagus (entrance to esophagus).

The pharynx is divided into three regions, which reflect the above borders. They are the:

    • Nasopharynx (choanae; soft palate),
    • Oropharynx (soft palate; faucial isthmus; superior margin of epiglottis & pharyngo-epiglottic folds),
    • Laryngopharynx (superior margin of epiglottis & pharyngo-epiglottic folds; inferior margin of cricoid cartilage).

MUSCLES:

The muscular wall of the pharynx consists of two layers: an outer layer of predominantly circular-oriented constrictors, and an inner layer of longitudinally oriented muscles that shorten and widen the pharynx.

The three pharyngeal constrictor muscles in the external layer of the pharynx surround the pharynx, and meet along a posterior midline pharyngeal raphe. When activated, the pharyngeal constrictor mm. serially constrict the lumen of the pharynx.

The superior pharyngeal constrictor m. consists of four parts, each arising from a distinct location (associated by name), and coalescing posteriorly to the superior portion of the pharyngeal raphe. The four distinct parts (and their anterior attachments) include the:

    • pterygopharyngeal part (pterygoid hamulus & occasionally the posterior aspect of the medial pterygoid plate),
    • buccopharyngeal part (pterygomandibular raphe),
    • mylopharyngeal part (posterior portion of mylohyoid line of the mandible), and the
    • glossopharyngeal part (posterolateral tongue).

The middle pharyngeal constrictor m. originates on the hyoid bone (greater and lesser horns) and the stylohyoid ligament, and inserts on the pharyngeal raphe.

The inferior pharyngeal constrictor m. consists of two parts. These parts (and their attachments) include the:

    • thyropharyngeal part (thyroid cartilage of the larynx), and the
    • cricopharyngeal part (cricoid cartilage of the larynx).

The three longitudinal muscles of the inner layer have a less coordinated anatomical arrangement than the constrictor muscles.


Stylopharyngeus m.

D1 S3 Chart Stylopharyngeus m.

Palatopharyngeus m.

D1 S3 Chart Palatopharyngeus m.

Salpingopharyngeus m.

D1 S3 Chart Salpingopharyngeus m.

NEUROVASCULATURE:

The pharyngeal constrictor mm. are innervated by the pharyngeal (neural) plexus, which receives efferent (motor) fibers from the vagus nn. (CN X) and afferent (sensory) fibers from the glossopharyngeal nn. (CN IX). The cricopharyngeal part of the inferior pharyngeal constrictor m. receives dual innervation from the pharyngeal (neural) plexus and the vagus n. (CN X) via the recurrent laryngeal n. and the superior laryngeal n. When activated, the pharyngeal constrictors serially constrict the lumen of the pharynx. Some fibers of the middle pharyngeal constrictor mm. can also act as an elevator of the pharynx. The plexus also receives autonomic fibers from the vagus n. (parasympathetic) and superior cervical ganglion (sympathetic).

The pharyngeal constrictor mm. are primarily supplied by the ascending pharyngeal a., a branch of the external carotid artery. Branches from the inferior thyroid a. also may supply the inferior pharyngeal constrictor m. Both superior and middle pharyngeal constrictor mm. may be partially supplied by tonsillar br. of the facial artery (also a branch of the external carotid a.). The superior pharyngeal constrictor m. may also receive blood from the ascending palatine a. (a br. of the facial a.).

The pharyngeal constrictor muscles are drained of blood by the pharyngeal venous plexus, which drains into the internal jugular vv.

FASCIA:

The pharynx is supported by two associated bodies of fascia: pharyngobasilar fascia and buccopharyngeal fascia. The pharyngobasilar fascia (the deep investing/epimysial layer of the external pharyngeal mm.) suspends the superior pharyngeal constrictor m. from the basilar part of the occipital bone and the adjacent temporal bone. The pharyngobasilar fascia is closely associated with the pharyngeal raphe at the pharyngeal tubercle. The buccopharyngeal fascia (the superficial investing/epimysial layer of the external pharyngeal mm.) consists of a thickened epimysium of the superior pharyngeal constrictor that extends anteriorly from the pharyngeal raphe to the superficial surface of the buccinator m. (of the cheek). A condensed band of the buccopharyngeal fascia that extends from the pterygoid hamulus to the posterior end of the mylohyoid line of the mandible is the pterygomandibular raphe. The pterygomandibular raphe connects the buccinator m. to the superior pharyngeal constrictor m.

RETROPHARYNGEAL SPACE:

The retropharyngeal space is a potential space posterior to the muscular wall of the pharynx (and its investing buccopharyngeal fascia), anterior to the prevertebral fascia, and spanning the distance between the base of the skull and the mediastinum (within the thoracic cavity). The retropharyngeal space is actually comprised of two potential spaces, separated by the alar fascia:

    • anterior, the “true” retropharyngeal space, and
    • posteriorly, the “danger space.”

The retropharyngeal space communicates laterally with the parapharyngeal spaces. Clinically, the retropharyngeal space is important, because it represents a potential pathway for metastasis of disease between the head & neck and the thorax.

2. What are the major targets and functions of the glossopharyngeal n. (CN IX) and vagus n. (CN X) in the neck?

Glossopharyngeal n. (CN IX):

    • Efferent to stylopharyngeus m.
    • Afferent from carotid sinus & body
    • Afferent from pharyngeal plexus

Vagus n. (CN X):

Efferent to pharyngeal plexus, pharyngeal mm. (excluding stylopharyngeus m.)

    • Superior laryngeal n.:
      • External br.
        • Efferent to inferior pharyngeal constrictor m.
        • Efferent to cricothyroid m. (intrinsic laryngeal muscle)
      • Internal br.
        • Afferent from laryngeal mucosa proximal to vocal folds
    • Recurrent laryngeal n.:
      • Efferent to all intrinsic laryngeal mm. (except cricothyroid m.)
      • Afferent from laryngeal mucosa distal to vocal folds

3. What is the carotid sheath, and what are its contents and associations with other structures of the neck?

The carotid sheath is a condensation of deep cervical fascia that surrounds the major vasculature of the neck. Contents include:

    • Common carotid a. (& the proximal internal carotid a.), medially,
    • Internal jugular v., laterally,
    • Vagus n. (CN X), posteriorly, and
    • Deep cervical lymph nodes.

The carotid sheath is found:

    • Deep to the SCM m.,
    • Lateral to the larynx, trachea, pharynx, esophagus, & infrahyoid mm.,
    • Posterior to the ansa cervicalis (sometimes ansa is embedded within the sheath), and
    • Anterolateral to the cervical sympathetic trunk.

4. Describe the neurovasculature (arteries and nerves) that serve the larynx.

The larynx is exclusively innervated by the vagus n., specifically by means of the:

    • Superior laryngeal n.:
      • External br.
        • Efferent to cricothyroid m. (intrinsic laryngeal muscle)
      • Internal br.
        • Afferent from laryngeal mucosa proximal to vocal folds
    • Recurrent laryngeal n.:
      • Efferent to all intrinsic laryngeal mm. (except cricothyroid m.)
      • Afferent from laryngeal mucosa distal to vocal folds

Blood supply to the larynx comes from two major sources:

    • Superior laryngeal a. (External carotid a. → Superior thyroid a. → Superior laryngeal a.)
      • Accompanied by the internal br. of the superior laryngeal n. through the thyrohyoid membrane.
    • Inferior laryngeal a. (1st part of SCA → Thyrocervical trunk → Inferior thyroid a. → Inferior laryngeal a.)
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5. Describe the laryngeal cartilages, membranes, & muscles. Describe how the intrinsic muscles of the larynx affect either the positions of the vocal ligaments, or vocal pitch.

CARTILAGES:

The cartilaginous laryngeal skeleton is comprised of nine major cartilages. Three cartilages makeup the bulk of the laryngeal skeleton. They are the:

Thyroid cartilage:

    • Most prominent cartilage
    • Formed from two laminae, united anteriorly along the midline (posteriorly, the cartilage is incomplete)
    • Suspended from the hyoid bone by the thyrohyoid membrane
    • Superior horns loosely articulate with the greater horns of hyoid
    • Inferior horns form the cricothyroid joint with the cricoid cartilage
    • Cricothyroid joint allows for thyroid cartilage to ‘tip’ forwards

Cricoid cartilage:

    • Forms a complete ring around the airway
      • Most robust posteriorly

Epiglottic cartilage:

    • Leaf-shaped cartilage
    • Sits posterior to thyroid cartilage
    • Forms the epiglottis
      • Forms a lid to cover the laryngeal inlet during deglutition (swallowing)

Three pairs of cartilages also help to support the structure and function of the larynx. They are the:

Arytenoid cartilages:

    • Pyramid-shaped
    • Sit atop the cricoid laminae (posterior)
    • Vocal process (attaches to vocal ligament)
    • Muscular process (allows for muscle attachment)
    • Capable of either rotation or gliding
      • For either abduction, or adduction of vocal cords

Corniculate cartilages:

    • Sit atop the arytenoid cartilages
    • Extend the structure provided by the arytenoids posteromedially
      • Posterior portion of the laryngeal inlet

Cuneiform cartilages:

    • Within the ary-epiglottic fold
    • Lateral portions of laryngeal inlet

MEMBRANES:

Two sheets of fibro-elastic connective tissue help to give shape to the walls of the larynx and laryngeal features: the quadrangular membrane and the conus elasticus.

The quadrangular membrane is a poorly defined fibro-elastic sheet spanning the space between the lateral margins of the epiglottis and the arytenoid cartilages. The inferior-most extent of the quadrangular membrane forms the vestibular ligaments.

The conus elasticus is a fibro-elastic sheet that shapes the walls of the larynx as a funnel between the thyroid and cricoid cartilages. The superior-most aspects of the conus elasticus are the vocal ligaments and the walls of the laryngeal ventricle. The anteromedial aspect of the conus elasticus is the (median) cricothyroid ligament, the connective tissue pierced during a cricothyrotomy.

INTRINSIC MM.:

Muscles that connect adjacent cartilages of the larynx are known as the intrinsic mm. of the larynx. These muscles either directly or indirectly affect the vocal ligaments, and therefore affect phonation (speech).

D1 S3 Chart INTRINSIC MM.
D1 S3 Chart INTRINSIC MM.

6. How is the sympathetic nervous system structured? What are the four basic pathways of pre-ganglionic sympathetic neurons? What are the major sources of sympathetics to the head & neck?

The sympathetic division of the autonomic nervous system consists of pre- and postganglionic fibers which typically (but not always) synapse in ganglia of the sympathetic trunk. Preganglionic fibers travel from the intermediolateral (IML) nucleus (lateral horn) of the spinal cord, out via the ventral roots of spinal nerves to the ventral primary rami (VPR), and then leave the spinal nerves via white rami communicantes (at levels T1-L2) to the sympathetic trunk. Once in the trunk, preganglionic fibers may:

    • synapse at that level of the sympathetic trunk and return to the VPR via a gray ramus communicans (or leave the trunk without synapsing as a splanchnic n.),
    • ascend the sympathetic trunk (and then either synapse and return to the VPR via a gray ramus communicans, or leave the trunk without synapsing as a splanchnic n.), or
    • descend the sympathetic trunk (and then either synapse and return to the VPR via a gray ramus communicans, or leave the trunk without synapsing as a splanchnic n.).

From the synapse, postganglionic fibers carry signals back to the VPR of the spinal nerve via gray rami communicantes. These fibers can then be distributed by the VPR. While white rami communicantes are restricted to the T1-L2 levels, the sympathetic trunks extend the entire length of the spinal cord, and gray rami communicantes conduct postganglionic fibers back to VPRs at every level of the cord. In the neck, there are typically 2-3 sympathetic ganglia, whereas in the thorax there are typically sympathetic ganglia at every spinal level (T1-T12).

Splanchnic nerves (collections pre-ganglionic fibers that pass through the sympathetic trunk without synapsing), typically synapse in the pre-aortic ganglia of the abdominopelvic cavity.

7. What is Horner’s syndrome, and what are its symptoms?

Horner’s syndrome is an interruption of a cervical sympathetic trunk, with potential symptoms of unilateral:

    • Miosis (constricted pupil),
    • Ptosis (droopy eyelid),
    • Pseudo-enopthalmos (appearance of sunken globe of eye), and
    • Anhydrosis (lack of sweating).