Robert is an anatomy professor at Benedictine University in Lisle, IL.
Lesson 20 - Pharynx, Larynx, Tongue
The pharynx is a half-cylindrical chamber made up of muscles and fascia that is attached superiorly to the basicranium, inferiorly to the esophagus, and laterally to the lateral margins of the nasal cavity, oral cavity, and larynx. The nasal cavities, oral cavity, and larynx open into the anterior part of the pharynx, and the esophagus opens into it inferiorly.
Learning Objectives - By the end of this lesson, you should be able to ...
- List the constrictor and longitudinal muscles of the pharynx, along with their origins, insertions, innervations, and actions.
- List and describe the nerves and vessels that supply the pharynx and larynx
- List and describe the cartilages of the larynx
- Describe how the pharynx functions during swallowing and how the larynx functions during speech
- Nasopharynx: part of the pharynx related to the nasal cavities. The nasopharynx is almost entirely surrounded by bone, and so it is sometimes called the bony nasopharynx. It is bordered by the palate anteriorly, the vomer, basioccipital, and associated parts of the sphenoid superiorly, and the anterior margin of the foramen magnum and cervical vertebral column posteriorly, and extends as far inferiorly as a line drawn between the hard palate and the anterior margin of the foramen magnum, where it borders the oropharynx. The opening for the pharyngotympanic tube, the levator veli palatini, and the soft palate are all in the nasopharynx.
- Oropharynx: part of the pharynx related to the oral cavity. The oropharynx is bordered superiorly by the nasopharynx, anteriorly by the oral cavity, and posteriorly by the vertebral column. It is continuous with the laryngopharynx at the level of the superior margin of the epiglottis. The palatine tonsils, lingual tonsils, palatopharyngeus muscle, and salpingopharyngeus muscle are in the oropharynx, as is the posterior portion of the tongue. The oropharynx is continuous with the laryngopharynx inferiorly.
- Laryngopharynx: part of the pharynx related to the larynx. The laryngopharynx is bordered superiorly by the oropharynx, anteriorly by the larynx and posterior portion of tongue (at the vallecula), posteriorly by the vertebral column, and inferiorly by the esophagus.
- Superior attachment: superiorly, the pharynx is attached to the basioccipital at the pharyngeal tubercle, the petrous part of the temporal bone, the cartilaginous part of the pharyngotympanic tube, the medial pterygoid plate, the pterygoid hamulus, and the pterygomandibular raphe, which runs between the pterygoid hamulus and the inside border of the mandible opposite the 3rd molar.
- Hyoid attachment: the pharynx attaches to the lower part of the stylohyoid ligament and the superior surfaces of the lesser and greater horns of the hyoid bone.
- Laryngeal attachment: the pharynx attaches to the oblique line of the thyroid cartilage and is reflected over the cricothyroid muscle onto the cricoid cartilage.
There are a number of muscles that form the wall of the pharynx and function to move it in one direction or another. With the exception of the stylopharyngeus muscle, these muscles are all innervated by the vagus nerve.
- Pharyngeal constrictors: there are three muscles that form the bulk of the pharynx: the superior constrictor, middle constrictor, and inferior constrictor muscles. They overlap one another, and, together, function to narrow the pharyngeal cavity. The superior constrictor attaches to the pterygoid hamulus, pterygomandibular raphe, and adjacent part of the inner border of the mandible; the middle constrictor attaches to the stylohyoid ligament and hyoid bone; and the inferior constrictor attaches to the laryngeal cartilages. Right and left constrictor muscles come together posteriorly at the pharyngeal raphe. Innervated by the vagus nerve.
- Stylopharyngeus: runs from the styloid process to insert on the deep surface of the pharyngeal wall, running between the superior and middle constrictor muscles. Innervated by the glossopharyngeal nerve. Elevates the pharynx.
- Salpingopharyngeus: runs from the pharyngotympanic tube to the pharyngeal wall. Innervated by the vagus nerve. Elevates the pharynx.
- Palatopharyngeus: runs from the soft palate to the pharyngeal wall. Innervated by the vagus nerve. Elevates the pharynx and depresses the soft palate.
Pharyngeal Nerves and Vessels
- Nerves: the glossopharyngeal nerve provides a motor branch to the stylopharyngeus muscle and sensory innervation to the oropharynx. The vagus nerve provides motor innervation to the other pharyngeal muscles (via the pharyngeal branch of X), and sensory innervation to the laryngopharynx (via the internal branch of the superior laryngeal nerve). Sensory innervation to the nasopharynx is from the pharyngeal branch of CN V2.
- Arteries: the blood supply of the upper pharynx is from branches of the external carotid artery - in particular, the ascending pharyngeal artery, branches of the facial artery, maxillary artery, and lingual artery. Blood supply to the lower pharynx is from the inferior thyroid artery, which is a branch of the subclavian artery.
- Veins: veins of the pharynx form a plexus which drains into the pterygoid plexus superiorly and the facial and internal jugular veins inferiorly.
- Thyroid: this cartilage is deficient in the back, so it covers the front and sides of the airway, and the pharyngeal constrictor muscles cover the back wall. The thyroid cartilage is made of two lamina that meet in the midline, and are taller laterally than in the midline. The thyroid cartilage has superior and inferior horns on each side - the superior horns attach to a ligament called the thyroid ligament, which binds the thyroid cartilage to the greater horns of the hyoid bone; and the inferior horns attach to the cricoid cartilage. The thyroid notch is the superior-most point in the midline where the two lamina meet, and it also marks the approximate location of the epiglottis on the inner surface of the thyroid cartilage.
- Epiglottis: this cartilage attaches to the insider border of the thyroid cartilage just behind the thyroid notch. It is covered with mucosa, and functions to block the airway during swallowing so that food and liquid cannot enter the trachea.
- Cricoid: the thyroid cartilage sits on top of the cricoid cartilage. Unlike the thyroid, the cricoid is a closed ring that is similar in superior view to the shape of the tracheal rings. The cricoid cartilage is shaped like a signet ring, and it is more substantial posteriorly than anteriorly. The arytenoid cartilages sit on top of the posterior part of the cricoid cartilage, and the vocal folds run from the arytenoid cartilages to the inner surface of the thyroid cartilage. The inferior horn of the thryoid cartilage articulates with the cricoid cartilage, and the thyroid cartilage can rock back and forth on the cricoid, thereby tensing and relaxing the vocal folds.
- Arytenoid: these two cartilages are triangle-shaped, and sit on top of the cricoid. The vocal folds attach to them, and run from their vocal processes to the back of the thyroid cartilage.
- Corniculate and cuneiform: the corniculate cartilages sit on top of the arytenoid cartilages, and the cuneiform cartilages sit in the mucosa that wraps around the epiglottis. Both of these cartilages are of minor importance in humans and we will not consider them further.
- Ligaments and joints: the thyrohyoid membrane links the hyoid bone to the thyroid cartilage. The internal branch of the superior laryngeal nerve and associated artery pierce the thyrohyoid membrane to supply the internal laryngeal structures. As noted previously, the thyroid rocks on the cricoid cartilage, and that movement occurs at a pair of joints formed at the attachment of the inferior horns of the thyroid to the cricoid. The arytenoid cartilages move at a joint between these cartilages and the cricoid, and the cricothyroid ligament attaches to the cricoid, thyroid, and vocal folds. There are a number of other less important ligaments and joints that we will not consider here.
Air is passed up the trachea into the larynx, and it flows through the space between the vocal folds, which is called the glottis. Under normal conditions, the vocal processes of the arytenoid cartilages point somewhat laterally, so that the vocal folds are slightly AB-ducted, and the glottis is open. During heavy expiration, the vocal processes of the arytenoid cartilages point further laterally, the vocal folds are fully AB-ducted, and the glottis is wide open. During phonation, the vocal processes of the arytenoid cartilages meet near the midline, AD-ducting the vocal folds and closing the glottis. This produces a sound in much the same way that air passed through the reed of a musical instrument or a split blade of grass produces a sound. The perceived pitch of that sound is largely dependent on the length of the vocal folds and the tension placed on them by the vocalis muscle which inserts along their length. The quality of one's voice can also be affected by the tension placed on the vocal folds by rocking of the thyroid cartilage back and forth on the cricoid, which relaxes and tenses the vocal folds, respectively.
Nerves and Vessels
- Nerves: superior laryngeal nerves split into internal branches and external branches above the hyoid bone. The external laryngeal nerves supply the inferior constrictor of the pharynx and the cricothyroid muscle, and the internal laryngeal nerves pierce the thyrohyoid membrane and supply the laryngeal cavity as far inferiorly as the vocal folds. The recurrent laryngeal nerves provide motor innervation to all of the laryngeal muscles except the cricothyroid, and sensory innervation to the larynx below the vocal folds. The left recurrent laryngeal nerve originates in the thorax, and the right recurrent laryngeal nerve arises in the root of the neck.
- Arteries: blood supply to the larynx is via the superior laryngeal artery, which is a branch of the superior thyroid artery off the external carotid, and the inferior laryngeal artery, which is a branch off the inferior thyroid artery off the subclavian artery.
- Veins: venous drainage from the larynx is via superior and inferior laryngeal veins, which drain into the superior and inferior thyroid veins, respectively. The superior thyroid veins drain into the internal jugular veins, and the inferior laryngeal veins drain into the brachiocephalic veins.
Muscles of the Oral Cavity and Tongue
There are three sets of muscles in the oral cavity to go over: (1) muscles that make up the floor of the oral cavity; (2) extrinsic muscles of the tongue; and (3) intrinsic tongue muscles. These muscles all act to support and/or move the tongue in the oral cavity. All but one of the extrinsic and intrinsic tongue muscles are innervated by the hypoglossal nerve (CN XII), whereas the two muscles that make up the floor of the oral cavity receive their innervation from elsewhere.
- Muscles that make up the floor of the oral cavity (2 muscles):
- Mylohyoid: runs from the mylohyoid line on the mandible's deep border to the hyoid. Innervated by the nerve to mylohyoid (CN V3)
- Geniohyoid: runs from the genial (tubercles/pits/spines) on the inside border of the chin region of the mandible to the hyoid body. Innervated by the anterior ramus of C1 spinal nerve.
- Extrinsic tongue muscles (4 muscles):
- Hyoglossus: runs from the greater horn and body of the hyoid bone to the lateral side of the tongue. Raises the hyoid and translates it anteriorly. Innervated by XII.
- Genioglossus: runs from the inside of the chin region of the mandible to the body of the hyoid bone and tongue. Raises the hyoid and translates it anteriorly. Innervated by XII.
- Styloglossus: runs from the styloid process to the lateral side of the tongue. Raises the hyoid and moves it posteriorly. Innervated by XII.
- Palatoglossus: runs from the palatine aponeurosis to the lateral side of the tongue. Raises the hyoid. Innervated by X.
- Intrinsic tongue muscles (3 muscles): There are longitudinal, transverse, and vertical muscles running within the tongue itself which move it in all directions. We will not consider these muscles further except to note that they are all innervated by CN XII.
This is our last lesson on the neck. Next, we turn our attentions to the upper limb, and after that the lower limb.
- Human Anatomy Lesson 21
Lesson #21 covers the shoulder, posterior scapular region, and axilla
- Human Anatomy Lesson 22
Lesson #22 covers the arm
- Human Anatomy Lesson 23
Lesson #23 covers the forearm, wrist, and hand
- Human Anatomy Lesson 24
Lesson #24 covers the gluteal region
- Human Anatomy Lesson 25
Lesson #25 covers the thigh
- Human Anatomy Lesson 26
Lesson #26 covers the leg and ankle
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© 2014 Robert McCarthy