The nasal cavity (or cavity of nose, latin: cavum nasi, cavitas nasi) is an irregular, bilateral air-filled space located above the roof of the mouth forming the internal part of the nose. The nasal cavity is an initial part of the respiratory tract and it also lodges the olfactory receptors providing the sense smell.
Most of the nasal cavity is lined with mucosa and it is a part of the upper airway passage. The nasal cavity communicates with all paranasal sinuses, including the ethmoidal air cells and the frontal, sphenoidal and maxillary sinuses.
The bony frame of the nasal cavity is formed by several bones of the skull, it is bounded by the nasal conchae laterally, cribriform plate of the ethmoidal bone superiorly, and the palatal processes of the maxilla and horizontal portion of the palatine bone inferiorly.
The nasal cavity has a vestibule and is bounded by six walls. The nasal vestibule is the most anterior part of the nasal cavity, which is covered by the nasal cartilage and lined with the same epithelium as the skin. The walls of the nasal cavity are formed by several bones of the skull, and the posterior and anterior walls open with large apertures. Anteriorly, the nasal cavity opens with the anterior nasal aperture (also known as the piriform aperture) and continues with the outer part of the nose. Posteriorly, the nasal cavity opens into the nasopharynx through a pair of oval openings called the choanae. The nasal cavity is separated in the middle by the nasal septum, which also forms the medial wall of each half of the cavity.
There are six walls forming the borders of the bony nasal cavity:
- roof (superior wall),
- floor (inferior wall),
- medial wall,
- lateral wall,
- anterior wall,
- posterior wall.
The roof of the nasal cavity is formed by the ethmoid and sphenoid bones. The anterior slope of the roof is formed by the cribriform plate of the ethmoid bone, while the posterior slope is formed by the anterior aspect of the body of the sphenoid.
The floor of the nasal cavity is formed by the palatine processes of the maxillae.
The medial wall of the nasal cavity corresponds to the nasal septum, which separates the cavity into two symmetrical parts. The bony nasal septum is formed by the vomer and the perpendicular plate of the ethmoid.
The lateral wall of the nasal cavity is formed by the nasal surface of the maxilla, the perpendicular plate of the palatine bone, the labyrinth of the ethmoid bone, the lacrimal bone, the medial plate of the pterygoid process, and the inferior nasal concha.
The anterior wall of the nasal cavity is formed by the nasal bone and the pair of anterior nasal apertures.
The posterior wall of the nasal cavity is formed by the body of the sphenoid and the paired openings called choanae.
Nasal concha and meatus
There are several formations in the nasal cavity that are shaped like curved shelves of bone called conchae or conchas. There are three nasal conchae on each lateral wall of the nasal cavity:
- superior nasal concha,
- middle nasal concha,
- inferior nasal concha.
The superior nasal conchae and the middle nasal conchae are a part of the labyrinth of the ethmoid bone, while the inferior nasal conchae are separate bones of the skull.
The nasal conchas project into the nasal cavity creating pathways along the lateral wall of the nasal cavity called nasal meatuses. There are five nasal meatuses.
- superior meatus,
- middle meatus,
- inferior meatus,
- common nasal meatus,
- nasopharyngeal meatus.
The superior meatus is the passage between the middle and superior nasal conchae.
The middle meatus is the pathway between the middle and inferior nasal conchae.
The inferior meatus lies between the inferior concha and the floor of the nasal cavity.
The common nasal meatus is the space between the conchae and the nasal septum.
And the nasopharyngeal meatus is the space where the superior, middle and inferior meatuses fuse behind the nasal conchae.
The first four of these passages are paired, while the nasopharyngeal meatus is a single pathway behind the conchae.
The nasal cavity is interconnected with other parts of the skull via openings, including:
- openings of ethmoidal cells,
- opening of frontal sinus,
- maxillary hiatus,
- nasolacrimal canal,
- openings of cribriform plate,
- incisive canal,
- piriform aperture,
- sphenopalatine foramen,
- opening of the sphenoidal sinus.
The openings of the nasal cavity connect each nasal meatus with different cavities or regions of the skull.
The superior nasal meatus is connected with the posterior ethmoidal cells.
The middle meatus presents openings to several paranasal sinuses:
- openings of anterior ethmoidal cells,
- openings of middle ethmoidal cells,
- opening of frontal sinus,
- maxillary hiatus that leads into the maxillary sinus.
The inferior meatus has an opening for the nasolacrimal canal, which connects the nasal cavity with the orbit.
The common nasal meatus presents the following openings:
- openings of cribriform plate - connects the nasal cavity with the anterior cranial fossa and transmits the olfactory nerves;
- incisive canal - connects the nasal cavity with the oral cavity, where it opens with the incisive foramen; transmits the nasopalatine nerve and greater palatine artery;
- piriform aperture (or anterior nasal aperture) - opens on the external aspect of the face, connects the nasal cavity with the nose and the outer environment;
The nasopharyngeal meatus features the following openings:
- sphenopalatine foramen - connects the nasal cavity with the pterygopalatine fossa, it transmits the sphenopalatine artery, and the nasopalatine and superior nasal nerves;
- choana - an opening of the nasal cavity to the external cranial base and nasopharynx;
- opening of sphenoidal sinus.
The sphenoidal sinus opens into a small space within the nasal cavity called the sphenoethmoidal recess, which lies superior and posterior to the superior nasal concha.
The arterial blood supply to the nasal cavity is provided by several arteries and their branches, which include:
- anterior and posterior ethmoidal branches of the ophthalmic artery supply the roof of the nasal cavity;
- sphenopalatine branch of the maxillary artery supplies the nasal mucosa;
- greater palatine branch of the maxillary artery supplies the region of the inferior meatus.
These arteries ramify to form anastomotic plexuses within the nasal mucosa such as the submucosal cavernous plexus in the posterior part of the septum and in the middle and inferior conchae, as well as numerous arteriovenous anastomoses in the deep layer of the mucosa.
The sensory nerves supplying different parts of the nasal cavity include:
- olfactory nerves - arise from the olfactory epithelium in the upper part of the nasal cavity and provide olfaction;
- anterior ethmoidal nerve, a branch of the nasociliary nerve - supplies the roof of the nasal cavity and gives off a lateral internal branch to supply the anterior part of the lateral wall and a medial internal branch to supply the nasal septum;
- infraorbital nerve - supplies the nasal vestibule;
- anterior superior alveolar nerve - supplies part of the nasal septum, the floor of the nasal cavity near the anterior nasal spine, and the anterior part of the lateral wall of the cavity;
- posterior superior nasal and posterior inferior nasal nerves, branches of the greater palatine nerve - supply the posterior part of the lateral wall, roof and floor of the nasal cavity, and the medial inferior part of the nasal septum;
- branches from the nerve of the pterygoid canal - supply the superior and posterior part of the roof of the nasal cavity and nasal septum.