Bones, Foramina & Canals

External Structure

The nose is the first organ of the respiratory system and the principal olfactory organ. It consists of a nasal skeleton, which houses the nasal cavity.

The nasal cavity has four functions:

1. Warms and humidifies the inspired air.
2. Removes and traps pathogens and particulate matter from the inspired air.
3. Responsible for sense of smell.
4. Drains and clears the paranasal sinuses and lacrimal ducts.

Lateral wall

• mostly consists of the maxilla. Also contributed to by perpendicular plate of the palatine bone, the medially pterygoid plate, the labyrinth of ethmoid and inferior concha.
• projecting out from the lateral walls into the nasal cavity are curved bony shelves termed nasal conchae.

Septum

Separates left and right nostrils of the nasal cavity. Consists of:

• Centrally – perpendicular plate of ethmoid
• Posteroinferioly – vomer bone
• Anteriorly – septal nasal cartilage
• Inferiorly – axillary crest – narrow bony strip projecting from maxilla and palatine bone along length of septum

Depressed by the depressor septi nasi muscle.

Floor (Hard palate)

• Posteriorly – palatine bone
• Anteriorly – palatine process of maxilla.

Roof

• cribiform plate of ethmoid bone.

Conchae (or turbinates) are curved bony shelves which project from the lateral walls on each side of the nasal cavity. 

Meati refers to the passages created beneath each of the corresponding nasal conchae. 

There are three separate conchae and respective meati – superior, middle and inferior.

Superior Concha & Meatus

• The concha is part of the medial surface of the labyrinth of the ethmoid bone.
• The meatus is short and the smallest, located between the middle and superior concha.

Middle Concha & Meatus

• The concha is also part of the medial surface of the labyrinth of the ethmoid bone.
• The meatus is middle-sized, located between the middle and inferior concha.
• Openings via the semilunar hiatus: frontal, maxillary and anterior ethmoidal sinuses.

Inferior Concha & Meatus

• Inferior conchae are considered a pair of facial bones.
• Inferior meatus is the largest, located beneath the inferior concha and above the nasal cavity floor.
• Broadest anteriorly and extends most of the length of the lateral wall.
• Openings via nasolacrimal duct

The OMC is the common pathway for ventilation and mucociliary drainage of a collection of structures.

Location

• Lateral wall of nasal cavity, deep to the middle concha.

Communications

• Anterior ethmoid air cells
• Maxillary sinus
• Frontal sinus
• Middle meatus

Boundaries

• Anterior – Agger nasi, atrium of middle meatus
• Superior – Basal lamella – a thin piece of lamina papyracea attaching to the middle concha to the lateral wall of nasal cavity.
• Posterior – Middle turbinate
• Floor – Inferior concha
• Medial – Middle concha
• Lateral – Lamina papyracea of the ethmoid sinuses

Landmarks

• Ethmoid bulla – lateral protuding middle ethmoidal sinus projecting over hiatus semilunaris and spanning the middle of the middle concha. Middle ethmoid sinuses empty into ethmoid bulla.
• Hiatus semilunaris – final drainage passage. Curved furrow continuous with the ethmoidal infundibulum. Located anteroinferiorly to ethmoid bulla and posterior to the uncinate process.
• Ethmoidal infundibulum – common channel that drains the ostia of the maxillary antra and anterior ethmoid air cells to the hiatus semilunaris
• Frontonasal duct
• Uncinate process – hook like process arising from posteromedial aspect of nasolacrimal duct.

• Concha bullosa – middle turbinate congenitally pneumatised.