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Home , External nasal nerve, Greater palatine canal, Inferior nasal concha, Lateral nasal cartilage, Lesser palatine arteries, Mylohyoid line

AND , , 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 3. Identify the conchae, meatuses, and openings of the paranasal sinuses and 4. Identify the openings of the auditory tube and and the nerve and blood supply to the nasal cavity, , and 5. Identify the pterygopalatine fossa, the location of the , and understand the distribution of terminal branches of the maxillary 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 or naris is the entrance to each nasal cavity and each nasal cavity communicates posteriorly with the nasopharynx through a or posterior nasal aperture. The roof of the nasal cavity is narrow and is represented by the nasal , of the ethmoid, and a portion of the sphenoid. The floor is the (consisting of the palatine processes of the and the horizontal portion of the ). The medial wall is represented by the nasal septum (Dissector p. 292, Fig. 7.69) and the lateral wall consists of the maxilla, , portions of the , the inferior , 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 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 . 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. – an old-fashioned “plow share” shaped bone that extends from the base of the body of the 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 (Dissector p. 292, Fig. 7.68, 7.69, 7.70).

35 4. Nerve and blood supply (Dissector p. 292, Fig. 7.69) a. – 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 , a branch of the . In addition to supplying the nasal septum, they pass through the incisive and foramen behind the anterior teeth (incisors) and supply the anterior part of the hard palate. They anastomose with branches of the and artery. b. Anterior ethmoidal artery and nerve (medial branches) – supply the anterior portion of the nasal septum (recall these as branches of the and ).

B. Lateral nasal wall 1. Nasal conchae or turbinates (Dissector pp. 293, 294; Figs. 7.71, 7.74) a. b. Parts of the ethmoid bone. c. 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. – between superior concha and body of sphenoid 3. Nerve and blood supply a. Posterior lateral nasal 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 and 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 via the o Opening of the anterior ethmoidal cells o Opening of the 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 . It is bounded anteriorly by the posterior surface of the maxilla, posteriorly by the pterygoid 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 (the combined greater petrosal nerve and ), and branches of the and artery. These nerve and artery branches are distributed to the floor of the , , 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 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 , 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 3. Identify the muscles of the floor of the mouth 4. Identify the sublingual and submandibular glands and their ducts 5. Identify the , , hypoglossal nerve, and 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. – for the , artery, and vein 2. Mylohyoid groove – for the nerve and artery of the mylohyoid 3. – a slight diagonal ridge for attachment of the 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. Locate and review the muscles of the floor of the oral cavity noting their fiber direction. 1. Mylohyoid – it attaches laterally to the mylohyoid line. Medially, its anterior and middle fibers attach to the midline mandibular raphe and its posterior fibers attach to the body of the hyoid. It is innervated by the nerve to the mylohyoid branch of the inferior alveolar nerve (along with anterior belly of digastric) 2. Geniohyoid – a slender pair of muscles that arise from the inferior mental spines and attach posteriorly to the body of the hyoid. They lay superior to the mylohyoid. It is innervated by C1 fibers conveyed to the oral cavity on the hypoglossal nerve.

B. Identify the openings of the salivary gland ducts in the mouth 1. Parotid duct (Stensen’s duct) – note a fleshy papilla projecting into the vestibule opposite the second upper molar tooth 2. Submandibular duct (Wharton’s duct) – terminates at the sublingual caruncle, a small projection just lateral to the frenulum of the tongue 3. Sublingual ducts (~12) – open on the summit of the sublingual fold, a fold of mucous membrane overlying the sublingual gland

C. Sublingual region (Dissector p. 302, Fig. 7.83) Next, incise the mucosa between the sublingual fold and the inner surface of the mandible. Start the incision at the frenulum of the tongue and stop near the 2nd mandibular molar tooth. Peel the mucosa medially to expose the sublingual gland. 1. Medial to the sublingual gland find the submandibular duct – follow the duct anteriorly to the sublingual caruncle and posteriorly into the deep portion of the submandibular gland. Note that the submandibular gland is folded around the posterior border of the mylohyoid muscle. 2. Expose the and find the lingual nerve. Trace it to the floor of the mouth. Note that it passes lateral, then inferior, and then medial to the submandibular duct before entering the tongue where it provides general sensation to the anterior 2/3s of the tongue. 3. Near the third mandibular molar tooth identify the submandibular ganglion that is “suspended” from the lingual nerve. Oftentimes, postganglionic glandular branches can be seen here entering the deep lobe of the submandibular gland. 4. Turn the specimen so that the submandibular triangle is exposed. Find the hypoglossal nerve and follow it into the sublingual region. Note that it passes between the hyoglossus and mylohyoid muscles to enter the floor of the mouth. The hypoglossal nerve is inferior to the course of the lingual nerve.

38 5. In the neck, locate the lingual artery arising from the external carotid near the tip of the greater horn of the hyoid (Dissector p. 302, Fig. 7.84). Trace the artery to where it passes deep to the hyoglossus muscle to enter the oral cavity. While deep to this muscle, it gives rise to the dorsal lingual branch to the posterior 1/3 of the tongue. Observe the artery as it emerges from the anterior border of the hyoglossus between it and the genioglossus muscle. Here, it gives rise to the deep lingual branch into the ventral surface of the tongue and the sublingual branch that supplies the floor of the oral cavity and sublingual gland.

D. Extrinsic muscles of the tongue (arise outside of the tongue and insert into it) (Dissector p. 302, Fig. 7.84; p. 303, Table 7.9) 1. Genioglossus – arises from the superior mental/genial spine and enters the tongue and also attaches to the body of the . It protrudes the tongue. 2. Hyoglossus – arises from the greater horn of the hyoid and inserts into the posterolateral side of the tongue. It depresses and retracts the tongue. 3. Styloglossus – attaches to the styloid process and enters the posterolateral surface of the tongue interdigitating with some of the fibers of the hyoglossus. It retracts and elevates the tongue. 4. Palatoglossus – attaches from the lateral border of the soft palate to the lateral margin of the tongue at the junction between its anterior 2/3s and posterior 1/3. It draws the soft palate downward to seal the oral cavity from the oropharynx. 5. Intrinsic muscles of the tongue – small muscles that begin and end in the tongue itself. They are arranged as vertical, transverse, superior longitudinal, and inferior longitudinal fibers. Collectively, they enable the tongue to change its shape. 6. Nerve supply – all intrinsic and extrinsic muscles of the tongue are skeletal muscle and are innervated by the hypoglossal nerve, EXCEPT the palatoglossus muscle, which is innervated by the vagus nerve.

E. Tongue (Dissector p. 301, Fig. 7.82) 1. Body – anterior 2/3s. The horizontal or oral part of the tongue. Its mucous membrane is thick on its dorsal surface and is covered by numerous lingual papillae. The mucous membrane on its ventral surface is thin. On the ventral surface of the tongue note the frenulum of the tongue. It is a mucosal fold that connects the tongue to the floor of the mouth. On either side of it anteriorly are the sublingual caruncles. 2. Root – posterior 1/3. The more vertical and pharyngeal part of tongue. Its mucous membrane is thin and beneath it are collections of lymphoid follicles representing the lingual tonsil. 3. Identify: • Sulcus terminalis – a “V”-shaped groove between anterior 2/3s and posterior 1/3 of tongue. • Foramen cecum – a blind pit located at the apex of sulcus terminalis. This is the site of the embryonic thyroglossal duct and development of the thyroid gland. • Circumvallate papillae – “Homer’s donuts” located just anterior to the sulcus terminalis. Taste buds within these papillae are innervated by the glossopharyngeal nerve.

39 PEER TEACHING GUIDE: 1. Demonstration of the 3 structural components of the nasal septum and nasal conchae. 2. Demonstration of the nerve and blood supply to the lateral and medial walls of the nasal cavity, including location of the sphenopalatine foramen and pterygopalatine ganglion. 3. Demonstration of the nasal meatuses, paranasal sinuses, and ostia of the paranasal sinuses and nasolacrimal duct. 4. Demonstration of the boundaries of the oral cavity. 5. Demonstration of the muscles of the floor of the mouth. 6. Demonstration of the sublingual and submandibular glands and their ducts. 7. Demonstration of the lingual nerve, the submandibular ganglion, the hypoglossal nerve, the course of the lingual artery and its deep lingual and sublingual branches. 8. Demonstration of the extrinsic muscles of the tongue. 6. Demonstration of the oral and pharyngeal parts of the tongue, the sulcus terminalis, foramen cecum, lingual papillae, including the circumvallate papillae, and the lingual tonsil

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