Gross Anatomy of the Pharynx Lecture Notes PDF

Gross Anatomy: Pharynx Page 1 of 10 Dr. Paul Walker Session Objectives By the end of this session, students will be able to accurately: 1. Describe the anatomy of the pharynx: divisions, boundaries, layers, muscles, gaps for stru...

Gross Anatomy: Pharynx Page 1 of 10 Dr. Paul Walker Session Objectives By the end of this session, students will be able to accurately: 1. Describe the anatomy of the pharynx: divisions, boundaries, layers, muscles, gaps for structures of passage, location of the tonsils, blood supply, innervation, relationship to cervical sympathetic ganglia & trunk, and lymphatic drainage. 2. Relate the anatomy of the pharynx to the swallowing mechanism learned in the gastrointestinal unit. 3. Apply understanding of pharyngeal anatomy to clinical problems of tonsil infections, tonsillectomy, substances lodged in the piriform recess, spread of disease in the retropharyngeal space, dysphagia, and the afferent/efferent limbs of the gag reflex. Session Outline I. Anatomy of the Pharynx A. Divisions, Boundaries, Layers B. Muscles of the Pharynx C. Gaps for Structures of Passage D. Locations of Tonsils E. Blood Supply of the Pharynx F. Innervation of the Pharynx G. Sympathetic Ganglia & Trunk H. Lymphatics of the Head & Neck II. Functions of the Pharynx A. Swallowing Mechanism III. Clinical Application of Pharyngeal Anatomy A. Tonsil Infections & Tonsillectomy B. Piriform Recess C. Retropharyngeal Space D. Dysphagia E. Gag Reflex Supplemental Reading Gray’s Anatomy for Students, 4th Ed (2020) Drake, Vogl, Mitchell (Elsevier). Ch 8 Scroll to section on Pharynx. Gross Anatomy: Pharynx Page 2 of 10 Dr. Paul Walker I. Anatomy of the Pharynx The pharynx is a fibromuscular tube connecting the nasal & oral cavities with respiratory & gastrointestinal systems, respectively. Extends from base of skull to C6 levels (~15 cm). Widest at the hyoid bone (C3) & narrowest at the entrance to the esophagus. Fig 1 (Gray’s Anatomy for Students) A. Divisions, Boundaries, Layers 3 Divisions w/ Boundaries 1. Nasopharynx: Posterior to nasal cavity Superior to soft palate 2. Oropharynx: Posterior to tongue Superior to epiglottis 3. Laryngopharynx: Posterior to larynx Superior to esophagus Layers of the Pharynx (1) Mucosa: Same covering as oral & nasal cavities. (2) Pharyngobasilar fascia: Thick fascia fills in gaps between pharyngeal muscles. Attaches pharynx to base of skull superiorly. (3) Muscular layer: Inner longitudinal and outer circular muscles. (4) Buccopharyngeal fascia: Posterior part of pretrachial fascia that permits movements of pharynx & contains the pharyngeal plexus of CN IX & X. The retropharyngeal space lies between the pretrachial fascia anteriorly and the prevertebral fascia posteriorly. It communicates with the superior mediastinum of the thorax. Gross Anatomy: Pharynx Page 3 of 10 Dr. Paul Walker B. Muscles of the Pharynx External (Outer) Constrictors Fig 2 (Gray’s Anatomy for Students) Superior Constrictor: Originates from pterygoid hamulus, pterygomandibular raphe & mandible. Middle Constrictor: Originates from the hyoid bone & stylohyoid ligament. Inferior Constrictor: Originates from thyroid and cricoid cartilages. All overlap as they insert posteriorly as a tendinous seam (pharyngeal raphe). Superior is innermost & inferior is outermost. Internal (Inner) Longitudinal Muscles: Stylopharyngeus: Originates from styloid process & inserts into the pharyngeal wall between superior & middle constrictor muscles Palatopharyngeus: Originates from the soft palate (palatine aponeurosis) & inserts into pharyngeal wall. Salpingopharyngeus: Originates from the auditory tube and blends with palatopharyngeus m. to insert into pharyngeal wall. Fig 3 (Gray’s Anatomy for Students) Gross Anatomy: Pharynx Page 4 of 10 Dr. Paul Walker C. Gaps for Structures of Passage Fig 4 (Gray’s Anatomy for Students) The oropharyngeal triangle is a triangular area bounded by the superior & middle constrictor muscles posteriorly and the mylohyoid muscle anteriorly where structures pass between neck/IT fossa and the oral cavity (Fig 4). Examples include lingual artery, lingual nerve, hypoglossal nerve among others. CN IX enters the oropharynx through the oropharyngeal triangle along with the stylopharyngeus muscle. Fig 5 (Gray’s Anatomy for Students) There are 3 other gaps related to the lateral regions of the constrictor muscles (Fig 5): Superior to the superior constrictor muscle is a gap that contains the opening of the auditory tube, levator veli palatini, tensor veli palatini, and salpingopharyngeus muscles. Between middle & inferior constrictor muscles is a gap that transmits the superior laryngeal artery and the internal laryngeal nerve into the laryngopharynx region. Inferior to the inferior constrictor muscle is a gap that contains the recurrent laryngeal nerve and associated vessels entering the larynx. Gross Anatomy: Pharynx Page 5 of 10 Dr. Paul Walker D. Location of Tonsils The nasopharynx, oropharynx, and oral cavity contain collections of lymphoid tissue (tonsils) that are part of the body’s defense system. Fig 6 (Gray’s Anatomy for Students) Pharyngeal (adenoids) tonsils located in roof of nasopharynx (Fig 6) Tubal tonsils near the opening of the auditory tube in the nasopharynx Palatine tonsils located between palatoglossal and palatopharyngeal folds (Fig 6). Lingual tonsils located in the pharyngeal tongue mucosa. E. Blood Supply of the Pharynx Fig 7 (Gray’s Anatomy for Students) 1. Ascending pharyngeal a. 2. Branches from facial a. (ascending palatine & tonsillar) 3. Branches from maxillary & lingual aa. 4. Branches from inferior thyroid a. Gross Anatomy: Pharynx Page 6 of 10 Dr. Paul Walker F. Innervation of the Pharynx Fig 8 (Gray’s Anatomy for Students) Pharyngeal Nerve Plexus (Fig 8) Located in buccopharyngeal fascia. Find the plexus in lab when you disarticulate & explore the region of the retropharyngeal space. CN X, inferior ganglia, & superior laryngeal branch CN IX & branches to oropharynx Also note the sensory nerve distribution to the 3 divisions of the pharynx: Nasopharynx CN V2 Oropharynx CN IX Laryngopharynx CN X Gross Anatomy: Pharynx Page 7 of 10 Dr. Paul Walker G. Sympathetic Ganglia & Trunk Fig 9 (Gray’s Anatomy for Students) You will find the superior cervical ganglion & sympathetic trunk embedded in the prevertebral fascia on the anterolateral surface of the vertebral bodies. Trace the trunk inferiorly to find the middle and inferior cervical ganglia and note vertebral levels and surrounding structures. You may have a fusion of the inferior cervical ganglion with the 1 st thoracic ganglion (stellate ganglion). Preganglionic cell bodies for head/neck SANS function are located at the superior part of the intermediolateral cell column (sources vary from T1-2, T1-3, T1- 4). These neurons send their VE axons into spinal nerves and enter the sympathetic trunk using a white rami communicans. Fig 10 (Gray’s Anatomy for Students) Preganglionic SANS axons ascend in the trunk until they reach the superior cervical sympathetic ganglion where they synapse onto postganglionic neurons of the ganglion. Postganglionic SANS fibers travel in gray rami communicantes to get into cervical spinal nerves (C2-C4) which deliver SANS axons to neck targets. Other fibers form a plexus around the internal & external carotid arteries associated with the carotid body & sinus. Postganglionic SANS fibers destined for the head/skull form a nerve called the carotid nerve which exits the top region of the superior cervical ganglion and forms a nerve plexus around the internal carotid artery as it enters the carotid canal. The carotid nerve can be found in lab and its fibers deliver postganglionic SANS axons that eventually converge to become the deep petrosal nerve. Gross Anatomy: Pharynx Page 8 of 10 Dr. Paul Walker II. Functions of the Pharynx Fig 11 (Netter) A. Swallowing Mechanism Oral Phase Involves instrinsic and extrinsic tongue muscle movements to prepare the bolus for entry into the oropharynx. Soft palate is elevated to prevent bolus from entering nasopharynx. Forms seal with palatopharyngeal sphincter (bulge in pharyngeal mucosa is known as Passavant’s ridge). Pharyngeal Phase Breathing ceases during this process. The pharynx is elevated by the inner longitudinal muscles. This action pulls the walls of the pharynx superiorly over the food bolus as the constrictor muscles move it inferiorly toward the esophagus. The cricopharyngeus m. is a specialized part of of the inferior constrictor m. that is considered the Upper Esophageal Sphincter and represents the superior site of esophageal constriction. This muscle relaxes as food passes from pharynx to the esophagus. CN X supplies motor innervation to 2 of the inner longitudinal pharyngeal muscles: palatopharyngeus and salpingopharyngeus. The stylopharyngeus muscle is innervated by a motor branch of CN IX. Dysphagia is the term for difficulty in swallowing. This can occur when the motor fibers of CN IX & X are damaged. Examples include diseases such as bulbar palsy (degeneration in medula). Dysphagia can also occur because of a physical object that impedes the swallowing process (e.g. tumor). Gross Anatomy: Pharynx Page 9 of 10 Dr. Paul Walker III. Clinical Applications of Pharyngeal Anatomy Fig 12 (Gray’s Anatomy for Students) A. Tonsil Infections & Tonsillectomy (Fig 12) Enlargement of the pharyngeal tonsils (adenoids) can partially obstruct airflow through the nasopharynx and produce mouth-breathing. This problem is common in children with recurring infections resulting in surgery to remove the pharyngeal tonsils. The position of the pharyngeal tonsils (and tubal tonsils) near the opening of the auditory tube (Fig 12) can facilitate the spread of infection into the middle ear cavity to cause otitis media. Chronic infections that require removal of the palatine tonsils (Fig 11-12) must be performed carefully since the tonsillar bed houses the palatine tonsils as well as the glossopharyngeal n. and vessels that must be isolated (cauterized) during surgery. B. Gag Reflex (Fig 12) The glossopharyngeal n. (CN IX) provides sensory innervation of the oropharynx and posterior tongue. Touching these areas activates the afferent limb of the gag reflex. The efferent limb is the vagus n. (CN X) that causes contractions of the pharyngeal muscles. Fig 13 (Gray’s Anatomy for Students) C. Piriform Recess (Fig 13) The laryngopharynx communicates with the larynx via the aditus (inlet) of the larynx. On each side of the aditus is the piriform recess, a pear-shaped depression where food must travel to enter the esophagus. Objects can become lodged in the piriform recess of the laryngopharynx. Sensory fibers from CN X give the feeling that “something is caught in the throat.” Gross Anatomy: Pharynx Page 10 of 10 Dr. Paul Walker Fig 14 (Gray’s Anatomy for Students) D. Retropharyngeal Space (Fig 14) The retropharyngeal space (RS) is located between the pretrachial and prevertebral fascia. The RS contains the pharyngeal plexus of nerves (IX, X). The loose connective tissue (buccopharyngeal fascia) of the RS permits movements of the pharynx during phonation and swallowing. The RS communicates inferiorly with the superior mediastinum of the thorax. RS infections (or tumors) interfere with swallowing and speaking and may spread inferiorly to the thorax.