Nose Anatomy and Function

Nose Anatomy and Function

• The nose is the beginning of the respiratory tract, located above the hard palate and contains the olfactory organ.
• Its components include the external nose and the nasal cavity, separated by the nasal septum.
• The nose is responsible for olfaction, respiration, filtering dust, humidifying air, and managing secretions from sinuses and nasolacrimal ducts.

External Nose Structure

• The external nose is the visible part that protrudes from the face, with a skeleton primarily made of cartilage.
• Size and shape vary due to differences in the cartilages.
• It extends from the root to the apex (tip).
• The nares (nostrils) are located on the inferior surface, bordered by the alae (wings).
• The root is bony and covered by thin skin, while the cartilages are covered by thicker skin with sebaceous glands.
• The vestibule contains vibrissae (stiff hairs) that filter dust; the transition from skin to mucous membrane occurs beyond the hairs.

External Nose Skeleton

• The bony part includes the nasal bones, frontal processes of the maxillae, the nasal part/spine of the frontal bone, and parts of the nasal septum.
• The cartilaginous part comprises two lateral cartilages, two alar cartilages, and the septal cartilage.
• Alar cartilages are U-shaped, mobile, and control the dilation/constriction of the nares.

Nasal Septum

• The nasal septum divides the nose into two nasal cavities, featuring both bony and cartilaginous parts.
• Its key components are the ethmoid's perpendicular plate, the vomer, and the septal cartilage.
• The ethmoid's perpendicular plate forms the superior part, descending from the cribriform plate.
• The vomer forms the postero-inferior part, with contributions from the maxillary and palatine bones.
• The septal cartilage connects to the bony septum through a tongue-and-groove joint.

Nasal Cavities

• The nasal cavity can refer to the entire cavity or each half.
• The nares provide anterior entry, and the choanae lead posteriorly into the nasopharynx.
• The mucosa lines the cavity, except for the vestibule, which is lined with skin.
• The mucosa is firmly attached to the bones and cartilages and 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.
• The respiratory area warms and moistens air.
• The olfactory area contains the olfactory organ, and sniffing enhances airflow to it.

Nasal Cavity Boundaries

• The roof is curved and narrow, formed by the frontonasal, ethmoidal, and sphenoidal bones, and hollow sphenoid body.
• The floor is wider, made up of the palatine processes of the maxilla and the palatine bone's horizontal plates.
• The medial wall is formed by the nasal septum.
• The lateral walls are made irregular by the nasal conchae/turbinates.

Nasal Cavity Features

• The nasal conchae (superior, middle, inferior) curve inferomedially, creating recesses called nasal meatuses.
• The nasal cavity includes the spheno-ethmoidal recess (posterosuperior), three nasal meatuses (superior, middle, inferior), and the common nasal meatus (medial).
• The inferior concha is the largest, an independent bone with vascular spaces.
• The middle and superior conchae are ethmoid bone processes.
• Mucosa swelling can block nasal passages.
• The spheno-ethmoidal recess houses the sphenoidal sinus opening.
• The superior nasal meatus is where the posterior ethmoidal sinuses open.
• The middle nasal meatus connects to the frontal sinus via the ethmoidal infundibulum/frontonasal duct.
• The semilunar hiatus is a groove where the frontal sinus opens.
• The ethmoidal bulla, caused by middle ethmoidal cells, is above the semilunar hiatus.
• The inferior nasal meatus receives the nasolacrimal duct.
• The common nasal meatus is the space where lateral passages open.

Nose Vasculature

• The arterial supply comes from five sources:
  • Anterior ethmoidal artery (ophthalmic artery)
  • Posterior ethmoidal artery (ophthalmic artery)
  • Sphenopalatine artery (maxillary artery)
  • Greater palatine artery (maxillary artery)
  • Septal branch of the superior labial artery (facial artery)
• The first three divide into lateral and medial (septal) branches.
• The greater palatine artery reaches the septum via the incisive canal.
• The Kiesselbach area (anterior septum) is where all five arteries anastomose, and is a common site for nosebleeds.
• The external nose is supplied by the first, fifth, and nasal branches of the infra-orbital/lateral nasal (facial) arteries.
• Venous drainage is provided by a submucosal plexus draining into the sphenopalatine, facial, and ophthalmic veins, regulating temperature/warming air.

Nose Innervation

• The nasal mucosa divides into postero-inferior and anterosuperior portions.
• The postero-inferior portion is innervated by the nasopalatine nerve (nasal septum) and posterior superior lateral nasal/inferior lateral nasal branches of the greater palatine nerve (lateral wall), which are from the maxillary nerve.
• The anterosuperior portion is innervated by the anterior and posterior ethmoidal nerves (nasociliary nerve/ophthalmic nerve).
• The external nose (dorsum/apex) is supplied by the infratrochlear nerve/external nasal branch of the anterior ethmoidal nerve (CN V1).
• The alae are supplied by the nasal branches of the infra-orbital nerve (CN V2).
• Olfactory nerves (CN I) originate in the olfactory epithelium, pass through the cribriform plate, and end in the olfactory bulb.

Paranasal Sinuses

• Paranasal sinuses are air-filled extensions of the nasal cavity into the frontal, ethmoid, sphenoid, and maxilla bones.
• The sinuses are named after the bones they are located in.

Frontal Sinuses

• Frontal sinuses are located in the frontal bone, behind the superciliary arches/root of the nose and are usually detectable in children by age 7.
• They drain into the ethmoidal infundibulum via the frontonasal duct, opening into the middle nasal meatus/semilunar hiatus.
• The sinuses are innervated by branches of the supra-orbital nerves (CN V1).
• The right and left sinuses differ in size, and the septum is not always in the median plane.
• They can extend into the greater wings of the sphenoid, with vertical/horizontal parts.

Ethmoidal Cells

• Ethmoidal cells (sinuses) are invaginations in the ethmoid bone between the nasal cavity and orbit and are usually not visible in plain radiographs before age 2 but are recognizable in CT scans.
• Anterior ethmoidal cells drain into the middle nasal meatus via the ethmoidal infundibulum.
• Middle ethmoidal cells open directly into the middle meatus and form the ethmoidal bulla.
• Posterior ethmoidal cells open directly into the superior meatus.
• The cells are supplied by the anterior and posterior ethmoidal branches of the nasociliary nerves (CN V1).

Sphenoidal Sinuses

• Sphenoidal sinuses are located in the body of the sphenoid and may extend into the wings of the bone.
• They are unevenly divided by a bony septum, and the body of the sphenoid is fragile due to pneumatization.
• The sinuses are separated from the optic nerves, pituitary gland, internal carotid arteries, and cavernous sinuses by thin bone plates.
• They develop from a posterior ethmoidal cell invading the sphenoid around age 2.
• Multiple posterior ethmoidal cells may invade the sphenoid, creating multiple sinuses that open separately into the spheno-ethmoidal recess.
• They are supplied by the posterior ethmoidal arteries and nerves.

Maxillary Sinuses

• Maxillary sinuses are the largest of the paranasal sinuses, located in the maxillae, communicating with the middle nasal meatus.
  • The 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, with conical elevations from tooth roots.
• Each drains into the middle nasal meatus via the semilunar hiatus by way of the maxillary ostium.
• The arterial supply is from superior alveolar branches of the maxillary artery, with the floor supplied by branches of the descending/greater palatine arteries.
• Innervation comes from the anterior, middle, and posterior superior alveolar nerves from the maxillary nerve.