Download Pharynx Larynx - Dr. Gudas

Stephen A. Gudas, PT, PhD Pharynx and Larynx REFERENCES: Moore and Agur, Essential Clinical Anatomy (ECA), 3rd ed., pp. 611 – 632. Grant’s Atlas 12 th ed., Figs 8.23 – 8.37 inclusive. Grant’s Dissector 14 th ed., pp. 234­240; 244­247; 252­255. OBJECTIVES – PHARYNX After studying the material of this lecture, the student will be able to: 1. 2. 3. 4. 5. 6. 7. 8. 9. Differentiate and describe the boundaries of the pharynx. Divide, anatomically, the pharynx into the following regions: nasopharynx, oropharynx, and laryngopharynx. Outline the osteology associated with the pharyngeal structures. Continue to describe the major bones, and their features and foramina, of the norma basalis view of the skull. Name the folds, ridges, recesses and associated structures of the pharynx. Outline the circumferential and longitudinal muscles of the pharynx. Discuss the role of the pharyngeal musculature in the act of deglutition (swallowing). Describe the sensory and motor innervation of the pharynx. Outline the blood supply of this region. OSTEOLOGY Study the norma basalis view of the skull. On the undersurface of the basilar occiput, there is a tubercle, the pharyngeal tubercle, which serves as a point of muscular attachment. The posterior nasal choanae, which connects the nasopharynx to the nasal cavity, is surrounded by the sphenoid, palatine, and vomer bases. The lateral and medial pterygoid plates form a pterygoid fossa that is filled in by the tensor palati muscle. There
is a prominent but small projection on the medial plate, the pterygoid hamulus. The styloid process of the temporal bone projects inferiorly and medially and three muscles attach to it. Also note the hyoid bone with the greater and lesser cornu (horns). BOUNDARIES Superiorly, the pharynx is bordered by the base of the occipital bone. Inferiorly, the pharynx is bordered by the esophagus and larynx at about the C6 level. Posteriorly lie the retropharyngeal space and the alar fascia. Anteriorly is the posterior nasal choanae, then the posterior 1/3 of the tongue, and most inferiorly lies the posterior surface of the larynx. REGIONS Note that the pharynx is a continuation of both the respiratory and digestive systems. Most superiorly, it receives the posterior opening of the nasal cavity (choanae), and is superior to the soft palate. This superior region is referred to as the nasopharynx. The region of the pharynx that you can visualize when looking into an individual’s mouth is posterior to the oral cavity, inferior to the soft palate, and superior to the epiglottic cartilage and is called the oropharynx. Most inferiorly, the region posterior to the larynx, inferior to the epiglottic cartilage, and superior to the level of the cricoid cartilage/C6 vertebra, is referred to as the laryngopharynx. The pharynx is lined with a mucous membrane. Ridges are referred to as folds, which are usually elevated by underlying structures. In the cadaver, post mortem changes may make identification of these folds difficult as they are best visualized and appreciated in the living. Note the following folds and structures in each part of the pharynx:
Nasopharynx: In addition to the posterior nasal choanae, there is the pharyngeal orifice of the auditory tube, with the torus tubarus projecting inferiorly from the orifice. Extending inferiorly from the torus is the salpingopharyngeal fold, and behind it a recess, the pharyngeal recess, that extends up to the superior limit of the pharynx. Pharyngeal tonsils, collections of lymphoid tissue that occur in the superior region of the nasopharynx, are popularly referred to as the adenoids. Oropharynx: In the oropharynx, the palatoglossal fold or arch extends from the palate to the tongue and is the first arch one sees when looking in the mouth. The palatopharyngeal fold is posterior to the palatoglossal fold and is the second arch visualized. The palatine tonsils lie between these two folds. The tonsils are likely absent from your cadaver as tonsils were routinely and probably unwisely removed in many individuals prior to the mid 1950’s. At the base of the tongue one can identify the midline median glossoepiglottic fold and the paired lateral glossoepiglottic folds, which keep the epiglottis solidly against the base of the tongue. The two spaces in between the median and lateral folds are the valleculae. Laryngopharynx: The pharynx surrounds the larynx on three sides, and the space on either of the lateral sides of the larynx is known as the piriform recess. MYOLOGY Pharyngeal Constrictors The muscles of the pharynx can be divided into two groups, three circumferentially oriented muscles (constrictors), and three longitudinally oriented muscles. Although not pharyngeal muscles, the muscles of the palate are closely related and are included due to their role in swallowing. The three constrictors all attach to the posteriorly arranged
median raphe, which attaches superiorly to the pharyngeal tubercle. All circumferential muscles can be said therefore to attach to this tubercle. The anterior attachments of these circumferential muscles are important. The superior pharyngeal constrictor originates from the pterygoid hamulus, the posterior end of the mylohyoid line of the mandible, and the pterygomandibular raphe, which extends between these bony structures. Recall that the buccinator attaches to the anterior aspect of this raphe. Also note that this raphe is one of the few in the body that does not lie in the midline and is therefore paired. The middle pharyngeal constrictor originates from the stylohyoid ligament and the greater and lesser horns of the hyoid bone. The inferior pharyngeal constrictor originates from the oblique line of the thyroid cartilage and the lateral surface of the cricoid cartilage. The constrictors can best be seen from a lateral view after the neck is carefully dissected. The inferior constrictor is the easiest to find and can be used as a guided to locate the other two. The constrictors, contracting in sequence from superior to inferior, squeeze the food bolus down into the esophagus. Note that the overlapping of the three constrictor muscles leaves four gaps in the pharyngeal musculature through which numerous structures enter/exit the pharynx. Study the various diagrams in the syllabus and a in your atlas to verify this. Superior to the superior constrictor: the gap between the superior constrictor and the base of the skull is closed by the pharyngobasilar fascia, through which pass the levator palati muscle and the auditory tube. These structures are difficult to observe from the lateral view or dissection, and best seen from the medial view of the nasopharynx in the split head. Between the superior and middle constrictors: passing between these muscles, which may be hard to separate from each other, are the stylopharyngeus muscle, and the nerve that innervates it, the glossopharyngeal nerve (C.N. IX). The nerve is more easily seen from the inside of the oropharynx as it travels to the base of the tongue. The muscle is found by palpating for and locating the styloid process in the cadaver (after very deep and careful dissection of the parotid bed), and tracing the stylopharyngeus to the side of the pharynx where it interdigitates with the circumferential muscles of the pharynx. Between the middle and inferior constrictors: the internal laryngeal nerve, which is a branch of the superior laryngeal
nerve, itself a branch of the vagus nerve, C.N. X, and the superior laryngeal artery, a branch of the superior thyroid artery, pass between the borders of this gap. These structures are easily seen in a lateral dissection of the neck. Inferior to the inferior constrictor: the recurrent laryngeal nerve, a branch of the vagus, can be found as it extends superiorly into the larynx. Longitudinal Muscles The longitudinal muscles of the pharynx all lie underneath previously described folds and have names identical to these folds. They insert into the side of the pharynx, and in reality all blend with one another as they descend inferiorly, so they can be said to all insert on the posterior superior borders of the thyroid cartilage. The palatopharyngeus originates from the hard palate and can be found under the palatopharyngeal fold; sometimes this muscle may be hard to dissect as the fold may be found wanting in the cadaver. The salpingopharyngeus originates from the cartilaginous portion of the auditory tube and can be seen descending from the inferior aspect of the torus tubarus in the nasopharynx. The stylopharyngeus originates outside the pharynx on the styloid process, one of three muscles attached to this pencil thin process. All three muscles elevate the pharynx in swallowing. It is a lay misconception that the epiglottis falls back and covers the additus of the larynx to protect the entrance of the respiratory entrance during swallowing. In reality the entire pharynx, larynx, and the hyoid bone all elevate by the action of the longitudinal pharyngeal muscles, plus others (stylohyoid, digastrics). Because of the attachments outlined above, the larynx and pharynx move superiorly and are pushed against the epiglottis, which is against the base of the tongue,
and the airway is effectively closed off in the process, preventing aspiration. This remarkable, coordinated sequence of muscular action is present at the moment of birth. The palatoglossus, not a pharyngeal muscle, elevates the tongue to assist the food bolus to reach the back of the oropharynx. The muscles of the palate are the muscularis uvulae, an insignificant muscle that elevates the uvula in singing, and the tensor palati and the levator palati. Although the two latter muscles are not true pharyngeal muscles per se, as they are located outside of the pharynx, their function in closing off the nasopharynx is integral to swallowing. The tensor palati originates from the scaphoid fossa and the lateral aspect of the cartilaginous auditory tube, descends and fills the pterygoid fossa, curves 90 degrees around the hamulus of the medial pterygoid plate, and then connects with its pair in a midline raphe in the soft palate. By its name, it tenses the palate, necessary for the action of the levator palati to be effective. The levator originates from the infratemporal surface of the temporal bone and the medial aspect of the cartilaginous auditory tube. It descends into the soft palate and interdigitates with the tensor. It elevates the palate that has been made taut. The two muscles thus close off the nasopharynx so that food does not enter the nasal cavity during swallowing. In dissection, from a medial view, the levator palati appears as if it is being poured out of the tube. INNERVATION All nerves of this area are part of what is loosely referred to as the pharyngeal plexus, which is a complex system of nerves that ramifies in and around the pharynx. It consists of cranial nerves as well as sympathetics from the autonomic nervous system. For motor innervation, all muscles described above are innervated by C.N X, the vagus, with the following exceptions. The stylopharyngeus is innervated by C.N IX, glossopharyngeal, and the tensor palati is innervated by the mandibular division of the trigeminal nerve, C.N V. For sensory innervation, the superior aspect of the nasopharynx is innervated by the pharyngeal nerve, a branch of V2, and most of the remaining pharyngeal mucosa is innervated by the glossopharyngeal nerve. The area surrounding the entrance to the larynx, including the aryepiglottic folds, is innervated by the internal laryngeal nerve, a branch of the vagus nerve. BLOOD SUPPLY The following arteries give blood supply to the pharynx: the ascending pharyngeal branch of the external carotid artery; the small tonsilar and palatine branches of the facial artery; the descending palatine branch of the maxillary artery; the pharyngeal artery from the maxillary artery; the superior thyroid artery from the external carotid artery; and the inferior thyroid artery from the thyrocervical trunk.
OBJECTIVES­ LARYNX After studying the material in this lecture, the student will be able to 1. 2. 3. 4. 5. Outline the three functions of the larynx. Describe, in detail, the cartilages and membranes of the larynx. Define the following spaces: laryngeal vestibule, laryngeal ventricle, rima glottis, and infraglottic cavity. Outline the origin, insertion, and functions of the muscles of the larynx. Describe the innervation and blood supply of the larynx. The larynx connects with oropharynx with the trachea for respiration; serves as a valve to protect the airway during swallowing; and is the organ for vocalization. CARTILAGES AND MEMBRANES The larynx is a tubular box made up of several cartilages and membranes, and one bone that hangs superiorly above the larynx proper. The hyoid bone is a u­shaped bone that lies superior to the thyroid cartilage. It has many muscles attaching to it, and its role in swallowing and laryngeal function is considerable. Inferior to the hyoid bone, the thyrohyoid membrane extends down to the superior border of the anterior aspect of the thyroid cartilage. This membrane is covered by the thyrohyoid muscle, one of the strap muscles of the neck (q.v.); the membrane is pierced by the superior laryngeal artery and the internal laryngeal nerve. The epiglottic cartilage is a large, tongue­shaped cartilage,
which attaches to the thyroid cartilage below by a stalk or petiolus, and to both this cartilage and the hyoid bone by ligaments. The thyroid cartilage is a large, single cartilage that has superior and inferior cornu, or horns, located at its posterior border and project superiorly and inferiorly respectively. The inferior cornu rests on the lamina of the cricoid cartilage, and can affect a rocking motion. The two thyroid lamina are fused anteriorly in the midline, and laterally each exhibits an oblique line for muscular attachment. The thyroid cartilage has a notch anteriorly, the thyroid notch (incisura), the lower point of which projects anteriorly rather prominently in males, named the laryngeal prominence of the thyroid cartilage (Adam’s apple). The cricoid cartilage is the only complete cartilaginous ring in the respiratory tree (tracheal rings are deficient posteriorly). The arch is located anteriorly, where it is smaller, and it broadens posteriorly to form the lamina. It is shaped like a signet ring. It exhibits superior facets for articulation with the arytenoid cartilages and lateral facets for articulation with the inferior cornu of the thyroid cartilage. The cricothyroid membrane extends superiorly from the inside of the cricoid cartilage and contributes to the conus elasticus of the vocal fold. The arytenoid cartilages are paired pyramidal shaped cartilages which are integral for voice production. The arytenoids have apical (superior), muscular (lateral), and vocal (anterior) processes. Each arytenoids rests on superior facets of the cricoid cartilage. The articulation of the arytenoids with the cricoid cartilages allows anterior­posterior, medial­lateral, rocking, and rotation movements. Accessory, vestigial cartilages include the cuneiform and corniculate cartilages, each paired, located within the aryepiglottic fold and at the top of the arytenoid cartilage respectively. The vocal ligament (paired) is a thickened band of elastic tissue connecting the anterior internal surface of the thyroid cartilage to the vocal process of the arytenoids cartilage posteriorly. When covered with mucosa, this forms the true vocal folds. The space between the vocal folds is called the rima glottidis. The distance between the vocal folds determines the pitch of the voice, a closer approximation causing a higher voice. The vestibular fold (paired) extends from the thyroid to the arytenoid cartilages and lies above the true vocal folds. The area between the true and false vocal folds is known as the ventricle of the larynx. The
quadrangular membrane (vestibular membrane) is a membrane extending superiorly from the false vocal folds. It is bounded superiorly by the aryepiglottic fold, anteriorly by the epiglottic cartilage, inferiorly by the false vocal folds, and posteriorly by the arytenoid cartilage. The conus elasticus is a layer of elastic tissue extending inferiorly from the vocal ligaments down to the inner lamina of the cricoid cartilage, blending in with the cricothyroid membrane. The area inferior to the true vocal folds is known as the infraglottic cavity. MYOLOGY The only extrinsic muscle of the larynx is the cricothyroid, originating on the external surface of the arch of the cricoid cartilage, and inserting into the external surface of the interior cornu and lamina of the thyroid cartilage. By rocking the thyroid cartilage forward on the cricoid, it tenses the vocal cord. The posterior cricoarytenoid extends from the posterior surface of the cricoid lamina to the muscular process of the arytenoid cartilage. By its pulling action, it rotates the arytenoids outwardly, thus opening the rima glottidis by separating the vocal folds, the only muscle to do so. The lateral cricoarytenoid muscle originates on the arch of the cricoid cartilage and extends posteriorly to the muscular process of the arytenoid cartilage. It lies behind the thyroid cartilage and cannot be seen unless the lamina of the thyroid cartilage is removed. By virtue of its position, it rotates the arytenoids in a direction opposite to that of the posterior cricoarytenoids, so therefore closes the rima glottidis by approximating the vocal folds. The arytenoideus stretches from the posterior border of the arytenoid cartilage to the posterior border of the opposite arytenoid cartilage. It has both transverse and
oblique fibres, the latter extending upward a bit. It slides the arytenoids together in a medial motion, thereby closing the rima glottidis by approximating the vocal folds. The aryepiglotticus muscle is a superior extension of the oblique arytenoideus, extending up into the aryepiglottic fold. It tenses the aryepiglottic fold, drawing it to the opposite aryepiglottic fold thereby assisting in closing the entrance to the larynx. This is an important action for swallowing to occur without aspiration. The thyroarytenoid muscle lies on the inside of the thyroid cartilage, above the lateral cricoarytenoid. It originates on the inner aspect of the lamina of the thyroid lamina and inserts on the arytenoid cartilage. It decreases tension of the vocal folds, much like a rubber band, when stretched, decreases its tension when the ends are drawn together. The thyroepiglotticus muscle is similar to the aryepiglotticus. It is a superior extension of the thyroarytenoid muscle extending up into the aryepiglottic fold. It too closes the entrance to the vestibule of the larynx by tensing the aryepiglottic fold and drawing it toward the opposite fold, thereby assisting in protecting the larynx in swallowing. Lastly, the vocalis muscle requires some thought. It is the most medial fibres of the thyroarytenoid muscle, lying right up against the vocal fold. It serves to adjust tension on localized segments of the vocal ligament. Think of the vocal ligament as a stretched elastic band. The thyroarytenoid decreases its tension, but the band is still tense even when approximated a bit. That part of the thyroarytenoid keeping this tension is the vocalis. INNERVATION AND BLOOD SUPPLY Motor innervation of the larynx is via the recurrent laryngeal nerve from C.N. X (Vagus) for all intrinsic muscles. The external laryngeal nerve, from the superior laryngeal nerve of the vagus innervates the lone external muscle of the larynx, the cricothyroid. For sensory innervation, the internal laryngeal nerve of the superior laryngeal nerve of the vagus supplies the area superior to the true vocal folds, and the recurrent laryngeal nerve of the vagus supplies the true vocal folds and the area inferior to them. The blood supply of the larynx is via the superior laryngeal artery, a branch of the superior thyroid artery (from the external carotid), to the area above the true vocal folds. The inferior laryngeal artery, a branch of the inferior thyroid artery (from the thyrocervical trunk), supplies the region of the true vocal folds and below.