Function
The nasal cavity conditions the air to be received by the areas
of the respiratory tract and nose. Owing to the large surface
area provided by the conchae, the air passing through the nasal
cavity is warmed or cooled to within 1 degree of body
temperature. In addition, the air is humidified, and dust and
other particulate matter is removed by vibrissae, short, thick
hairs, present in the vestibule. The cilia of the respiratory
epithelium move the particulate matter towards the pharynx where
it is swallowed.
Borders
The lateral wall of the nasal cavity is mainly made up by the
maxilla, however there is a deficiency that is compensated by:
the perpendicular plate of the palatine bone, the medial
pterygoid plate, the labyrinth of the ethmoid and the inferior
concha. The nasal cavity is enclosed by the nasal bone above.
The floor of the nasal cavity, which forms the roof of the
mouth, is made up by the bones of the hard palate: the
horizontal plate of the palatine bone posteriorly and the
palatine process of the maxilla anteriorly. To the front of the
nasal cavity is the nose, while the back is continuous with the
pharynx. The paranasal sinuses are connected to the nasal cavity
through small orifices called ostia.
The nasal cavity is divided in two by a vertical fin called the
nasal septum. On the sides of the nasal cavity are three
horizontal outgrowths called turbinates or conchae (singular "concha").
These turbinates disrupt the airflow, directing air toward the
olfactory epithelium on the surface of the turbinates and the
septum. The vomeronasal organ is located at the back of the
septum and has a role in pheromone detection.
Cilia and mucus along the inside wall of the nasal cavity trap
and remove dust and pathogens from the air as it flows through
the nasal cavity. The cilia move the mucus down the nasal cavity
to the pharynx, where it can be swallowed.
The nasal cavity is divided into two segments: the respiratory
segment and the olfactory segment. The respiratory segment is
lined with ciliated pseudostratified columnar epithelium (also
called respiratory epithelium). The conchae are located in this
region. The respiratory segment has a very vascularized lamina
propria allowing the venous plexuses of the conchal mucosa to
engorge with blood, restricting airflow and causing air to be
directed to the other side of the nose. This cycle occurs
approximately every 20-30 minutes. Nose bleeds in the inferior
concha are common in this region. The olfactory segment is lined
with a specialized type of pseudostratified columnar epithelium,
known as olfactory epithelium, which contains receptors for the
sense of the smell. This segment is located along the dorsal
roof of the nasal cavity. Histological sections appear
yellowish-brown due to the presence of lipofuscin pigments.
Olfactory mucosal cell types include: bipolar neurons,
supporting (sustentacular) cells, basal cells, and Bowman's
glands. The axons of the bipolar neurons form the olfactory
nerve (cranial nerve I) which enters the brain through the
cribiform plate. Bowman's glands are serous glands in the lamina
propria, whose secretions trap and dissolve oderiferous
substances.
Blood and nerve supply
There is a rich blood supply to the nasal cavity. In some
animals, such as dogs, the capillary beds flowing through the
nasal cavity help cool the blood flow to the brain.
Blood supply comes from branches of both the internal and
external carotid artery, including branches of the facial artery
and maxillary artery. The named arteries of the nose are:
Sphenopalatine artery, a branch of the maxillary artery.
Anterior ethmoidal artery, a branch of the ophthalmic artery
Branches of facial artery supplying the vestibule of the nasal
cavity.
[edit] Innervation
Innervation of the nasal cavity responsible for the sense of
smell is via the olfactory nerve, which sends microscopic fibers
from the olfactory bulb through the cribiform plate to reach the
top of the nasal cavity.
General sensory innervation is by branches of the trigeminal
nerve (V1 & V2):
Nasociliary nerve (V1)
Nasopalatine nerve (V2)
Posterior nasal branches of Maxillary nerve (V2)
The entire nasal cavity is innervated by autonomic fibers.
Sympathetic innervation to the blood vessels of the mucosa
causes them to constrict, while parasympathetic innervation of
the mucosa controls secrection by mucous glands.
Diseases
Diseases of the nasal cavity include viral infections and nasal
cavity cancer.
Empty nose syndrome.
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