NOSEThe nose is the part of the respiratory tract superior to the hard palate and contains the peripheral organ of smell. It includes the external nose and nasal cavities, which are divided into right and left cavities by the nasal septum. Each nasal cavity is divisible into an olfactory area and a respiratory area. The functions of the nose and nasal cavities are:

Olfaction (smelling).

Respiration (breathing).

Filtration of dust.

Humidification of inspired air.

Reception and elimination of secretions from the nasal mucosa, paranasal sinuses, and nasolacrimal ducts.

External Nose

The external nose varies considerably in size and shape, mainly because of differences in the nasal cartilages. The dorsum of the nose extends from its superior angle, the root, to the apex (tip) of the nose. The inferior surface of the nose is pierced by two piriform (L. pear-shaped) openings, the nares (nostrils, anterior nasal apertures), which are bound laterally by the alae (wings) of the nose and separated from each other by the nasal septum. The external nose consists of bony and cartilaginous parts.

The bony part of the nose consists of the:

Nasal bones.

Frontal processes of the maxillae.

Nasal part of the frontal bone and its nasal spine.

Bony part of the nasal septum.

The cartilaginous part of the nose consists of five main cartilages: two lateral cartilages, two alar cartilages, and a septal cartilage. The U-shaped alar cartilages are free and movable; they dilate or constrict the nares when the muscles acting on the nose contract.

Nasal Cavities

The nasal cavities, entered through the nares, open posteriorly into the nasopharynx through the choanae. Mucosa lines the nasal cavities, except the nasal vestibule, which is lined with skin. The nasal mucosa is firmly bound to the periosteum and perichondrium of the supporting bones and cartilages of the nose. The mucosa is continuous with the lining of all the chambers with which the nasal cavities communicate: the nasopharynx posteriorly, the paranasal sinuses superiorly and laterally, and the lacrimal sac and conjunctiva superiorly. The inferior two thirds of the nasal mucosa is the respiratory area, and the superior one third is the olfactory area. Air passing over the respiratory area is warmed and moistened before it passes through the rest of the upper respiratory tract to the lungs. The olfactory area is specialized mucosa containing the peripheral organ of smell; sniffing draws air to the area. The central processes of the olfactory receptor neurons in the olfactory epithelium unite to form nerve bundles that pass through the cribriform plate and enter the olfactory bulb.

The boundaries of the nasal cavity are as follows:

The roof of the nasal cavity is curved and narrow, except at the posterior end; the roof is divided into three parts (frontonasal, ethmoidal, and sphenoidal), which are named from the bones that form each part.

The floor of the nasal cavity is wider than the roof and is formed by the palatine process of the maxilla and the horizontal plate of the palatine bone. The medial wall of the nasal cavity is formed by the nasal septum, the the main components of which are the perpendicular plate of the ethmoid, vomer, septal cartilage, and the nasal crests of the maxillary and palatine bones. The lateral wall of the nasal cavity is uneven because of the nasal conchae (superior, middle, and inferior) three elevations that project inferiorly like scrolls. The conchae curve inferomedially, each forming a roof for a meatus, or recess.

The nasal conchae (L. shells) divide the nasal cavity into four passages: sphenoethmoidal recess, superior nasal meatus, middle nasal meatus, and inferior nasal meatus. The sphenoethmoidal recess, lying superoposterior to the superior concha, receives the opening of the sphenoidal sinus. The superior nasal meatus is a narrow passage between the superior and the middle nasal conchae (parts of the ethmoid bone) into which the posterior ethmoidal sinuses open by one or more orifices. The middle nasal meatus is longer and deeper than the superior one. The anterosuperior part of this passage leads into the ethmoidal infundibulum, an opening through which it communicates with the frontal sinus, via the frontonasal duct. The semilunar hiatus (L. hiatus semilunaris) is a semicircular groove into which the frontonasal duct opens. The ethmoidal bulla (L. bubble), a rounded elevation located superior to the semilunar hiatus, is visible when the middle concha is removed. The bulla is formed by middle ethmoidal cells, which constitute the ethmoidal sinuses. The maxillary sinus also opens into the posterior end of the semilunar hiatus. The inferior nasal meatus is a horizontal passage, inferolateral to the inferior nasal concha (an independent, paired bone). The nasolacrimal duct from the lacrimal sac opens into the anterior part of this meatus.

The arterial supply of the medial and lateral walls of the nasal cavity is from branches of the sphenopalatine artery, anterior and posterior ethmoidal arteries, greater palatine artery, superior labial artery, and the lateral nasal branches of the facial artery. On the anterior part of the nasal septum is an area rich in capillaries (Kiesselbach area) where all five arteries supplying the septum anastomose.

This area is often where profuse bleeding from the nose occurs. A rich plexus of veins drains deep to the nasal mucosa into the sphenopalatine, facial, and ophthalmic veins.

The nerve supply of the posteroinferior half to two thirds of the nasal mucosa is chiefly from CN V2 by way of the nasopalatine nerve to the nasal septum and posterior lateral nasal branches of the greater palatine nerve to the lateral wall. The anterosuperior part of the nasal mucosa (both the septum and lateral wall) is supplied by the anterior ethmoidal nerves, branches of CN V1.

Paranasal Sinuses

The paranasal sinuses are air-filled extensions of the respiratory part of the nasal cavity into the following cranial bones: frontal, ethmoid, sphenoid, and maxilla. They are named according to the bones in which they are located.

The frontal sinuses are between the outer and the inner tables of the frontal bone, posterior to the superciliary arches and the root of the nose. Each sinus drains through a frontonasal duct into the ethmoidal infundibulum, which opens into the semilunar hiatus of the middle meatus. The frontal sinuses are innervated by branches of the supraorbital nerves (CN V1).

The ethmoidal cells (sinuses) include several cavities that are located in the lateral mass of the ethmoid between the nasal cavity and the orbit. The anterior ethmoidal cells drain directly or indirectly into the middle meatus through the infundibulum. The middle ethmoidal cells open directly into the middle meatus. The posterior ethmoidal cells, which form the ethmoidal bulla, open directly into the superior meatus. The ethmoidal sinuses are supplied by the anterior and posterior ethmoidal branches of the nasociliary nerves (CN V1).

The sphenoidal sinuses, unevenly divided and separated by a bony septum, occupy the body of the sphenoid bone; they may extend into the wings of this bone in the elderly. Because of these sinuses, the body of the sphenoid is fragile. Only thin plates of bone separate the sinuses from several important structures: the optic nerves and optic chiasm, the pituitary gland, the internal carotid arteries, and the cavernous sinuses. The posterior ethmoidal artery and nerve supply the sphenoidal sinuses.

The maxillary sinuses are the largest of the paranasal sinuses. These large pyramidal cavities occupy the bodies of the maxillae. The apex of the maxillary sinus extends toward and often into the zygomatic bone. The base of the maxillary sinus forms the inferior part of the lateral wall of the nasal cavity. The roof of the maxillary sinus is formed by the floor of the orbit. The floor of the maxillary sinus is formed by the alveolar part of the maxilla. The roots of the maxillary teeth, particularly the first two molars, often produce conical elevations in the floor of the maxillary sinus. Each sinus drains by an opening, the maxillary ostium, into the middle meatus of the nasal cavity by way of the semilunar hiatus. Because of the superior location of this opening, it is impossible for the sinus to drain when the head is erect until the sinus is full. The arterial supply of the maxillary sinus is mainly from superior alveolar branches of the maxillary artery; however, branches of the greater palatine artery supply the floor of the sinus. Innervation of the maxillary sinus is from the anterior, middle, and posterior superior alveolar nerves, branches of CN V2.