Nose Anatomy and Function

Nose Composition & Function

• The nose is the portion of the respiratory tract located above the hard palate, containing the peripheral organ of smell.
• It consists of the external nose and the nasal cavity, divided by the nasal septum.
• Functions include olfaction, respiration, air filtration and humidification, and drainage for paranasal sinuses and nasolacrimal ducts.

External Nose

• The external nose's skeleton is primarily cartilaginous, with size variations due to differences in the cartilages.
• The dorsum nasi extends from the root to the apex (tip).
• Nares (nostrils) are pear-shaped openings on the inferior surface, bordered by the alae (wings).
• The superior bony part is covered by thin skin, while the cartilaginous part has thicker skin with sebaceous glands.
• The skin extends into the nasal vestibule, containing stiff hairs (vibrissae) that filter dust.

Skeleton of External Nose

• The supporting structure consists of bone and hyaline cartilage.
• Bony parts include the nasal bones, frontal processes of maxillae, nasal part/spine of the frontal bone, and bony parts of the nasal septum.
• Cartilaginous parts include two lateral, two alar, and one septal cartilage.
• The U-shaped alar cartilages can dilate or constrict the nares upon muscle contraction.

Nasal Septum

• Divides the nose into two nasal cavities, comprised of bony and cartilaginous parts.
• Main components are the perpendicular plate of the ethmoid, the vomer, and the septal cartilage.
• The perpendicular plate descends from the cribriform plate.
• The vomer forms the postero-inferior part with contributions from the maxillary and palatine bones.
• Septal cartilage articulates with the bony septum.

Nasal Cavities

• The nasal cavity has anterior entry via the nares and posterior opening into the nasopharynx via the choanae.
• It is lined with mucosa, except for the nasal vestibule which has skin.
• The nasal mucosa is firmly bound to the periosteum and perichondrium of the supporting structures.
• The mucosa connects to the nasopharynx, paranasal sinuses, lacrimal sac, and conjunctiva.
• The inferior two thirds is the respiratory area, while the superior one third is the olfactory area.

Boundaries of Nasal Cavities

• The roof is narrow and curved, formed by the frontonasal, ethmoidal, and sphenoidal bones.
• The floor is wider, formed by the palatine processes of the maxilla and horizontal plates of the palatine bone.
• The medial wall is the nasal septum.
• The lateral walls are irregular due to the nasal conchae (superior, middle, and inferior).

Features of Nasal Cavities

• Nasal conchae project inferomedially, dividing the cavity into recesses or meatus.
• There are five passages: spheno-ethmoidal recess, superior/middle/inferior meatus, and a common nasal meatus.
• The inferior concha is largest, formed by an independent bone, and its mucosa contains vascular spaces that can affect nasal cavity caliber.
• Middle and superior conchae are medial processes of the ethmoid bone.
• Swelling of the conchae mucosa can block nasal passages.
• The spheno-ethmoidal recess receives the opening of the sphenoidal sinus.
• The superior nasal meatus receives openings from posterior ethmoidal sinuses.
• The middle nasal meatus connects to the frontal sinus via the ethmoidal infundibulum.
• The semilunar hiatus is a groove into which the frontal sinus opens.
• The ethmoidal bulla, formed by middle ethmoidal cells, is located superior to the semilunar hiatus.
• The inferior nasal meatus receives the opening of the nasolacrimal duct.
• The common nasal meatus is the space between the conchae and septum.

Vasculature of Nose

• Arterial supply comes from five sources.
• Anterior and posterior ethmoidal arteries (from the ophthalmic artery).
• Sphenopalatine artery (from the maxillary artery).
• Greater palatine artery (from the maxillary artery).
• Septal branch of the superior labial artery (from the facial artery).
• These arteries divide into lateral and medial (septal) branches.
• The greater palatine artery reaches the septum via the incisive canal.
• Kiesselbach area in the anterior septum is an anastomotic arterial plexus.
• External nose also receives blood from listed arteries and branches of the infra-orbital and facial arteries.
• Venous drainage is via the sphenopalatine, facial, and ophthalmic veins.
• The submucosal venous plexus is important for thermoregulation.
• Venous blood from the external nose drains into the facial vein.

Innervation of Nose

• Nasal mucosa divides into postero-inferior and anterosuperior portions, supplied by different nerves.
• The postero-inferior gets its supply mainly from the maxillary nerve, via the nasopalatine nerve and lateral nasal branches of the greater palatine nerve.
• The anterosuperior gets its supply from the ophthalmic nerve (CN V1), via the anterior and posterior ethmoidal nerves.
• The external nose is supplied by CN V1 (infratrochlear nerve, external nasal branch of anterior ethmoidal nerve) and CN V2 (nasal branches of the infra-orbital nerve).
• Olfactory nerves arise from cells in the olfactory epithelium and pass through the cribriform plate to the olfactory bulb.

Paranasal Sinuses

• These are air-filled extensions of the nasal cavity into the frontal, ethmoid, sphenoid, and maxillary bones.

Frontal Sinuses

• Located between the outer and inner tables of the frontal bone.
• Usually detectable in children by age 7.
• Drain via the frontonasal duct into the ethmoidal infundibulum, opening into the middle nasal meatus.
• Innervated by branches of the supra-orbital nerves (CN V1).
• Rarely of equal size, vary in size, and the septum between them is not usually in the median plane.

Ethmoidal Cells

• Small invaginations of the mucous membrane into the ethmoid bone.
• Usually not visible in plain radiographs before age 2.
• Anterior cells drain into the middle nasal meatus through the ethmoidal infundibulum.
• Middle cells open directly into the middle meatus, forming the ethmoidal bulla.
• Posterior cells open directly into the superior meatus.
• Supplied by the anterior and posterior ethmoidal branches of the nasociliary nerves (CN V1).

Sphenoidal Sinuses

• Located in the body of the sphenoid, may extend into the wings.
• Unevenly divided by a bony septum, making the sphenoid body fragile.
• Thin plates of bone separate the sinuses from optic nerves/chiasm, pituitary gland, internal carotid arteries, and cavernous sinuses.
• Derived from a posterior ethmoidal cell invading the sphenoid at approximately age 2.
• May have multiple sinuses opening separately into the spheno-ethmoidal recess.
• Supplied by the posterior ethmoidal arteries and nerves.

Maxillary Sinuses

• The largest of the paranasal sinuses, located in the bodies of the maxillae.
• Apex extends toward the zygomatic bone.
• The base forms the inferior part of the lateral nasal wall.
• The roof is the floor of the orbit.
• The floor is the alveolar part of the maxilla; tooth roots may create elevations.
• Drain into the middle nasal meatus via the semilunar hiatus.
• Arterial supply mainly from superior alveolar branches of the maxillary artery.
• Innervation from the anterior, middle, and posterior superior alveolar nerves (branches of the maxillary nerve).