NASAL CAVITY AND PARANASAL SINUSES, PTERYGOPALATINE FOSSA, AND ORAL CAVITY (Grant's Dissector [16th Ed.] pp. 290-294, 300-303) TODAY’S GOALS (Nasal Cavity and Paranasal Sinuses): 1. Identify the boundaries of the nasal cavity 2. Identify the 3 principal structural components of the nasal septum 3. Identify the conchae, meatuses, and openings of the paranasal sinuses and nasolacrimal duct 4. Identify the openings of the auditory tube and sphenopalatine foramen and the nerve and blood supply to the nasal cavity, palatine tonsil, and soft palate 5. Identify the pterygopalatine fossa, the location of the pterygopalatine ganglion, and understand the distribution of terminal branches of the maxillary artery and nerve to their target areas DISSECTION NOTES: General comments: The nasal cavity is divided into right and left cavities by the nasal septum. The nostril or naris is the entrance to each nasal cavity and each nasal cavity communicates posteriorly with the nasopharynx through a choana or posterior nasal aperture. The roof of the nasal cavity is narrow and is represented by the nasal bone, cribriform plate of the ethmoid, and a portion of the sphenoid. The floor is the hard palate (consisting of the palatine processes of the maxilla and the horizontal portion of the palatine bone). The medial wall is represented by the nasal septum (Dissector p. 292, Fig. 7.69) and the lateral wall consists of the maxilla, lacrimal bone, portions of the ethmoid bone, the inferior nasal concha, and the perpendicular plate of the palatine bone (Dissector p. 291, Fig. 7.67). The conchae, or turbinates, are recognized as “scroll-like” extensions from the lateral wall and increase the surface area over which air travels through the nasal cavity (Dissector p. 293, Fig. 7.71). The superior 1/3 of the nasal mucosa is olfactory in function and the remainder is respiratory (Dissector p. 292, Fig. 7.69). The mucosa is very vascularized and contains numerous glands. Paranasal sinuses are membrane-lined, air-filled spaces within portions of the sphenoid, ethmoid, frontal, and maxillary bones. They communicate with the nasal cavity and are drained by ostia that open into the meatuses and recesses of the lateral nasal wall (Dissector p. 293, Fig. 7.72). I. Nasal Cavity In the previous lab, the head was bisected sagittally with the goal of producing one side that contains an intact nasal septum and another side that exposes the lateral nasal wall. Since most of the neurovasculature of the nasal cavity courses within the mucosal lining and is small, you will find it difficult to see and/or trace these structures. Refer to an atlas or drawing for the general pattern of distribution. Inspect the following structures of the nasal septum and lateral nasal wall. A. Nasal septum 1. Divides the nasal cavity into right and left cavities 2. Represents the medial wall of the nasal cavity 3. Consists of cartilage (hyaline) and bone covered by mucous membrane (Dissector p. 292, Figs. 7.69, 7.70): a. Vomer – an old-fashioned “plow share” shaped bone that extends from the base of the body of the sphenoid bone to the hard palate. It forms the posterior edge of the nasal septum. b. Perpendicular plate of ethmoid – descends from the roof of the nasal cavity and attaches to the vomer and septal cartilage anteriorly. c. Septal cartilage – forms the anterior portion of the nasal septum and is continuous with the lateral nasal cartilages (Dissector p. 292, Fig. 7.68, 7.69, 7.70). 35 4. Nerve and blood supply (Dissector p. 292, Fig. 7.69) a. Nasopalatine nerve – a branch of V2 that enters the nasal cavity from the pterygopalatine fossa via the sphenopalatine foramen. The nerve crosses the roof of the nasal cavity before it descends obliquely down the nasal septum accompanied by the sphenopalatine artery, a branch of the maxillary artery. In addition to supplying the nasal septum, they pass through the incisive canal and foramen behind the anterior teeth (incisors) and supply the anterior part of the hard palate. They anastomose with branches of the greater palatine nerve and artery. b. Anterior ethmoidal artery and nerve (medial branches) – supply the anterior portion of the nasal septum (recall these as branches of the ophthalmic artery and nasociliary nerve). B. Lateral nasal wall 1. Nasal conchae or turbinates (Dissector pp. 293, 294; Figs. 7.71, 7.74) a. Superior nasal concha b. Middle nasal concha Parts of the ethmoid bone. c. Inferior nasal concha 2. Spaces relative to the conchae a. Superior meatus – inferior to the superior concha b. Middle meatus - inferior to the middle concha c. Inferior meatus - inferior to the inferior concha d. Sphenoethmoidal recess – between superior concha and body of sphenoid 3. Nerve and blood supply a. Posterior lateral nasal arteries and nerves enter the nasal cavity from the pterygopalatine fossa through the sphenopalatine foramen which is located posterior to the middle concha. b. Anterior ethmoidal artery and nerve (lateral branches) – supply the anterior lateral portion of the lateral nasal wall (recall these as branches of the ophthalmic artery and nasociliary nerve). The external nasal nerve is a branch that passes between the nasal bone and lateral nasal cartilage to supply skin to the tip of the nose. c. CN I – the olfactory nerve supplies the olfactory epithelium which covers the superior concha and adjacent portion of the nasal septum. 4. Openings/ostia of the paranasal sinuses and nasolacrimal duct – approach these by cutting horizontally partially through the conchae and hinging them to view the meatuses (Dissector p. 293, 294; Figs. 7.72, 7.73) a. Superior meatus – openings of the posterior ethmoidal cells b. Middle meatus • Ethmoidal bulla – a projection of the ethmoidal bone into the middle meatus. It contains openings of the middle ethmoidal cells • Semilunar hiatus – curved slit in front and below the ethmoidal bulla. Within the semilunar hiatus identify: o Opening of the frontal sinus via the frontonasal duct o Opening of the anterior ethmoidal cells o Opening of the maxillary sinus c. Inferior meatus – slit-like opening of the nasolacrimal duct d. Sphenoethmoidal recess – opening of the sphenoidal sinus 36 II. Pterygopalatine Fossa and Sphenopalatine Foramen Be able to locate this small, but important pyramidal space on a dry skull. It is bounded anteriorly by the posterior surface of the maxilla, posteriorly by the pterygoid process of the sphenoid, and medially by the perpendicular plate of the palatine bone. It contains the pterygopalatine ganglion (a parasympathetic ganglion), the terminal portion of the nerve of the pterygoid canal (the combined greater petrosal nerve and deep petrosal nerve), and branches of the maxillary nerve and artery. These nerve and artery branches are distributed to the floor of the orbit, face, nasal cavity, and palate via numerous openings. Strip away the mucous membrane behind the middle concha and locate the sphenopalatine foramen transmitting neurovascular branches to the nasal cavity. Along the inferior aspect of this foramen, break through the bone (of the perpendicular plate of the palatine bone) to open the greater palatine canal transmitting the descending palatine artery (which divides to give rise to the greater and lesser palatine arteries) and greater and lesser palatine nerves to the hard and soft palate, respectively. Retrace and follow the greater and lesser palatine nerves superiorly to locate the pterygopalatine ganglion (Dissector p. 298, Fig. 7.80). This ganglion is the site of synapse of presynaptic axons of the greater petrosal nerve (branch of CN VII). Postsynaptic axons from the pterygopalatine ganglion distribute with branches of the maxillary nerve where they stimulate secretion from the mucosa of the nasal cavity, paranasal sinuses, nasopharynx, roof of mouth, and soft palate. This ganglion also stimulates the lacrimal gland. Hyperactive stimulation of this ganglion to cause vasodilation and increased secretion has earned it the name, “hayfever” ganglion. III. Oral Cavity TODAY’S GOALS (Oral Cavity): 1. Identify the boundaries of the oral cavity 2. Identify the relevant bony landmarks on the inner surface of the mandible 3. Identify the muscles of the floor of the mouth 4. Identify the sublingual and submandibular glands and their ducts 5. Identify the lingual nerve, submandibular ganglion, hypoglossal nerve, and lingual artery 6. Identify the extrinsic muscles of the tongue 7. Identify the oral and pharyngeal parts of the tongue, the sulcus terminalis, foramen cecum, lingual papillae, including the circumvallate papillae, and the lingual tonsil General comments: The oral cavity is the region anterior to the oropharynx. It consists of the oral vestibule and the oral cavity proper. Oral Cavity (Dissector p. 300, Fig. 7.81) – General description: A. Oral vestibule – the “U”-shaped space between the lips and cheeks and teeth and gums. It communicates across the teeth and around the third molar teeth with the: B. Oral cavity proper – the area between the alveolar processes of the mandibular teeth C. Boundaries of the oral cavity: 1. Superiorly – hard palate 2. Anteriorly and laterally – teeth and gums 3. Posteriorly – palatoglossal folds 4. Inferiorly – floor of mouth consisting of the mylohyoid and geniohyoid muscles D. Bony landmarks on mandible (Dissector p. 257, Fig. 7.28) 37 1. Mandibular foramen – for the inferior alveolar nerve, artery, and vein 2. Mylohyoid groove – for the nerve and artery of the mylohyoid 3. Mylohyoid line – a slight diagonal ridge for attachment of the mylohyoid muscle 4. Sublingual fossa – a slight depression on the anterior inner surface of the mandible above the mylohyoid line that the sublingual gland rests against 5. Submandibular fossa – a slight depression on the posterior inner surface of the mandible below the mylohyoid line that the submandibular gland rests against 6. Mental or genial spines (superior and inferior) – anterior attachment points for the genioglossus (superior spines) and geniohyoid muscles (inferior spines) DISSECTION NOTES: A.