External Nose
The external nose (nasus externus) has a complex osteocartilaginous structure.
The bony skeleton forms the upper part. It is formed by the paired nasal bones, which define the shape of the dorsum, and the frontal processes of the maxilla laterally.
The cartilaginous skeleton includes the lateral nasal cartilages (cartilago nasi lateralis) and the greater alar cartilages (cartilago alaris major). The lateral cartilages fill the upper angle of the piriform aperture and are closely connected to the septum. An important clinical point: if the cartilaginous part of the septum is destroyed, a characteristic deformation develops — saddle nose.
The skin covering is heterogeneous:
- Root of the nose: skin is thin and mobile. Subcutaneous tissue here lacks fat, containing vessels, nerves, and muscles instead.
- Tip and alae: skin is thick, firmly fused with the underlying cartilages, and contains numerous sebaceous glands.
- Vestibule: near the nostrils, the skin turns inward, becoming covered with stiff, short hairs (vibrissae).
The blood supply is characterized by rich anastomoses. Branches of the ophthalmic artery (a. dorsalis nasi) connect with the facial artery. Venous drainage proceeds via the external nasal veins into the facial vein, and from there via the ophthalmic veins directly into the cavernous sinus of the brain. Sensitivity is supplied by branches of the trigeminal nerve (specifically, n. infratrochlearis and n. ethmoidalis anterior).
Walls of the nasal cavity
The nasal cavity (cavitas nasi) is divided by the nasal septum (septum nasi) into two often asymmetric halves. Posteriorly, it opens into the nasopharynx via the choanae (choanae).
- The medial wall is the nasal septum itself.
- The superior wall (roof) is assembled from several bones (from anterior to posterior): nasal bones, frontal processes of the maxillae, frontal bone, cribriform plate (lamina cribrosa ossis ethmoidalis), and the body of the sphenoid bone. The latter features an aperture leading into the sphenoidal sinus.
- The inferior wall (floor) simultaneously serves as the roof of the oral cavity. Anteriorly, it is formed by the palatine processes of the maxilla (forming the anterior nasal spine); posteriorly, by the horizontal plates of the palatine bones (forming the posterior nasal spine).
- The lateral wall is the most complex. It separates the nasal cavity from the orbit and the maxillary sinus (sinus maxillaris). It is formed by the lacrimal bone, orbital plate of the ethmoid bone, frontal process of the maxilla, perpendicular plate of the palatine bone, and the medial plate of the pterygoid process. The opening of the maxillary sinus on this wall is partially covered by the inferior nasal concha.
Nasal conchae and meatuses
On the lateral wall, there are three nasal conchae (conchae nasales): superior, middle (both are parts of the ethmoid bone), and inferior (a separate bone). The spaces underneath them form the nasal meatuses.
- Superior nasal meatus (meatus nasi superior): the shortest one. The sphenoidal sinus and posterior ethmoidal cells open here. At the same level posteriorly lies the sphenopalatine foramen (foramen sphenopalatinum), leading into the pterygopalatine fossa.
- Middle nasal meatus (meatus nasi medius): beneath the middle concha lies the semilunar hiatus (hiatus semilunaris). The frontal sinus opens into its anterosuperior part, and the maxillary sinus into its posteroinferior part. The anterior and some of the middle ethmoidal cells also open here.
- Inferior nasal meatus (meatus nasi inferior): located between the inferior concha and the nasal floor. The nasolacrimal duct (canalis nasolacrimalis) opens here. It is precisely through this meatus that surgeons insert catheters for posterior nasal packing.
Mucous membrane
The mucous membrane is tightly fused with the periosteum of the bony walls and continues into the paranasal sinuses. Topographically, it is divided into two zones:
- Respiratory region (regio respiratoria): occupies the majority of the area. Here the mucosa is very thick (especially on the inferior concha) and structurally resembles cavernous, spongy tissue.
- Olfactory region (regio olfactoria): localized in the superior parts (roof, superior concha, superior part of the septum). It has a yellowish tint and contains the receptor apparatus.
Briefly: answers to topical questions
Which arteries supply blood to the mucous membrane of the nasal cavity?
The mucous membrane of the nasal cavity is supplied by branches of the ophthalmic and sphenopalatine arteries.
- Ophthalmic artery (a. ophthalmica) — gives off the anterior ethmoidal artery (a. ethmoidalis anterior), whose branches (rr. nasales posteriores laterales and rr. septales anteriores) supply the lateral wall and septum.
- Sphenopalatine artery — gives off the posterior septal branch (a. nasalis posterior septi).
Which nerves provide sensory innervation to the mucous membrane of the nasal cavity?
Sensory innervation to the mucous membrane of the nasal cavity is provided by branches of the ophthalmic and maxillary nerves.
- Nasociliary nerve (n. nasociliaris) — a branch of the ophthalmic nerve, gives off the anterior ethmoidal nerve (n. ethmoidalis anterior), which divides into internal nasal branches (rr. nasales interni).
- Infraorbital nerve (n. infraorbitalis) — a branch of the maxillary nerve, gives off external and internal nasal branches (rr. nasales externi et interni).
- Nasal branches (rr. nasales posteriores superiores) — originate in the pterygopalatine ganglion.
- Nasopalatine nerve (n. nasopalatinus) — innervates the mucous membrane of the nasal septum.
Which cartilages form the skeleton of the external nose?
The cartilaginous skeleton of the external nose includes several paired and accessory cartilages.
- Lateral nasal cartilage (cartilago nasi lateralis) — a paired triangular cartilage forming the dorsum and ala of the nose.
- Greater alar cartilage (cartilago alaris major) — a paired cartilage surrounding the nostrils, consisting of medial and lateral crura.
- Lesser alar cartilages (cartilagines alares minores) — attach to the lateral crus of the greater alar cartilage in the posterosuperior parts of the ala.
- Accessory nasal cartilages (cartilagines nasi accessoriae) — may be present additionally.
How to memorize the openings: everything "posterosuperior" opens into the superior meatus (sphenoidal sinus, posterior cells), the "anterior and large" structures open into the middle meatus (frontal, maxillary), and only tears drain into the inferior meatus (nasolacrimal duct).
Class and exam questions
Into which nasal meatus does the maxillary sinus open?
Into the middle nasal meatus. The opening is located in the posteroinferior part of the semilunar hiatus (hiatus semilunaris).
What happens if the cartilaginous part of the nasal septum is destroyed?
This will lead to the loss of support for the dorsum of the external nose and the formation of a deformity clinically known as a "saddle nose".
What forms the inferior wall of the nasal cavity?
The floor of the nasal cavity is formed by the palatine processes of the maxilla anteriorly and the horizontal plates of the palatine bones posteriorly.
What else to study on this topic
- Features of the venous bed of the external nose and its connection with the cavernous sinus.
- Topography of the sphenopalatine foramen and its communications.
- Detailed structure of the bony lateral wall of the nasal cavity.
- Histotopographic features of the spongy tissue in the respiratory region of the mucosa.
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