The term "nasal cavity" can refer to each of the two cavities of the nose, or to the two sides combined. in the
coronal plane, showing the ostiomeatal complex (green area) The lateral wall of each nasal cavity mainly consists of the
maxilla. However, there is a deficiency that is compensated for by the perpendicular plate of the
palatine bone, the
medial pterygoid plate, the
labyrinth of ethmoid and the
inferior concha. The
paranasal sinuses are connected to the nasal cavity through small orifices called
ostia. Most of these ostia communicate with the nose through the lateral nasal wall, via a semi-lunar depression in it known as the
semilunar hiatus. The hiatus is bound laterally by a projection known as the
uncinate process. This region is called the
ostiomeatal complex. The roof of each nasal cavity is formed in its upper third to one half by the
nasal bone and more inferiorly by the junctions of the upper lateral cartilage and nasal septum. Connective tissue and skin cover the bony and cartilaginous components of the
nasal dorsum. The floor of the nasal cavities, which also form 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. The most anterior part of the nasal cavity is the
nasal vestibule. The vestibule is enclosed by the
nasal cartilages and lined by the same
epithelium of the
skin (stratified squamous, keratinized). Within the vestibule, this changes into the typical respiratory epithelium that lines the rest of the nasal cavity and
respiratory tract. Inside the
nostrils of the vestibule are the
nasal hair, which filter dust and other matter that are breathed in. The back of the cavity blends, via the
choanae, into the
nasopharynx. The nasal cavity is divided in two by the vertical
nasal septum. On the side of each nasal cavity are three horizontal outgrowths called
nasal conchae (singular "concha") or turbinates. 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. The nasal cavity has a
nasal valve area that includes an
external nasal valve and an
internal nasal valve. The external nasal valve is bounded medially by the
columella, laterally by the
lateral nasal cartilage, and posteriorly by the nasal sill. The internal nasal valve is bounded laterally by the caudal border of the lateral nasal cartilage, medially by the dorsal
nasal septum, and inferiorly by the anterior border of the
inferior turbinate. The internal nasal valve is the narrowest region of the nasal cavity and is the primary site of nasal resistance.
Segments The nasal cavity is divided into two segments: the respiratory segment and the olfactory segment. • The respiratory segment comprises most of each nasal cavity, and is lined with ciliated pseudostratified columnar epithelium (also called
respiratory epithelium). The conchae, or turbinates, are located in this region. The turbinates have a very vascularized lamina propria (erectile tissue) allowing the venous plexuses of their mucosa to engorge with blood, restricting airflow and causing air to be directed to the other side of the nose, which acts in concert by shunting blood out of its turbinates. This
cycle occurs approximately every two and a half hours. • 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 in and beneath the mucosa of the roof of each nasal cavity and the medial side of each middle turbinate. 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
cribriform plate. Bowman's glands are serous glands in the lamina propria, whose secretions trap and dissolve odoriferous substances.
Blood supply There is a rich blood supply to the nasal cavity. 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 and
greater palatine artery, branches of the
maxillary artery. •
Anterior ethmoidal artery and
posterior ethmoidal artery, branches of the
ophthalmic artery • Septal branches of the
superior labial artery, a branch of the
facial artery, which supplies the vestibule of the nasal cavity.
Nerve supply 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
cribriform plate to reach the top of the nasal cavity. General sensory innervation is by branches of the
trigeminal nerve (V1 and V2): •
Nasociliary nerve (V1) •
Anterior ethmoidal nerve from the nasociliary nerve (V1) • Posterior nasal branches of
maxillary nerve (V2) The nasal cavity is innervated by autonomic fibers.
Sympathetic innervation to the blood vessels of the mucosa causes them to
constrict, while the control of secretion by the
mucous glands is carried on
postganglionic parasympathetic nerve fibers originating from the
facial nerve. == Function ==