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The nasal cavity is a large, air-filled space above and behind the
nose A nose is a protuberance in vertebrates that houses the nostrils, or nares, which receive and expel air for respiration alongside the mouth. Behind the nose are the olfactory mucosa and the sinuses. Behind the nasal cavity, air next passe ...
in the middle of the face. The nasal septum divides the cavity into two cavities, also known as fossae. Each cavity is the continuation of one of the two nostrils. The nasal cavity is the uppermost part of the
respiratory system The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies g ...
and provides the nasal passage for inhaled air from the nostrils to the nasopharynx and rest of the respiratory tract. The
paranasal sinuses Paranasal sinuses are a group of four paired air-filled spaces that surround the nasal cavity. The maxillary sinuses are located under the eyes; the frontal sinuses are above the eyes; the ethmoidal sinuses are between the eyes and the sph ...
surround and drain into the nasal cavity.


Structure

The term "nasal cavity" can refer to each of the two cavities of the nose, or to the two sides combined. 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 sinus Paranasal sinuses are a group of four paired air-filled spaces that surround the nasal cavity. The maxillary sinuses are located under the eyes; the frontal sinuses are above the eyes; the ethmoidal sinuses are between the eyes and the spheno ...
es 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 cartilages of the nose 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 concha In anatomy, a nasal concha (), plural conchae (), also called a nasal turbinate or turbinal, is a long, narrow, curled shelf of bone that protrudes into the breathing passage of the nose in humans and various animals. The conchae are shaped lik ...
e (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 The vomeronasal organ (VNO), or Jacobson's organ, is the paired auxiliary olfactory (smell) sense organ located in the soft tissue of the nasal septum, in the nasal cavity just above the roof of the mouth (the hard palate) in various tetrapo ...
is located at the back of the septum and has a role in pheromone detection.


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. In some animals, such as dogs, the
capillary A capillary is a small blood vessel from 5 to 10 micrometres (μm) in diameter. Capillaries are composed of only the tunica intima, consisting of a thin wall of simple squamous endothelial cells. They are the smallest blood vessels in the bod ...
beds flowing through the nasal cavity help cool the blood flow to the
brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...
. 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 A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the ...
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 & 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 Mucous gland, also known as muciparous glands, are found in several different parts of the body, and they typically stain lighter than serous glands during standard histological preparation. Most are multicellular, but goblet cells are single-ce ...
is carried on postganglionic parasympathetic nerve fibers originating from the facial nerve.


Function

The two nasal cavities condition the air to be received by the other areas of the respiratory tract. Owing to the large surface area provided by the
nasal concha In anatomy, a nasal concha (), plural conchae (), also called a nasal turbinate or turbinal, is a long, narrow, curled shelf of bone that protrudes into the breathing passage of the nose in humans and various animals. The conchae are shaped lik ...
e (also known as turbinates), the air passing through the nasal cavity is warmed or cooled to within 1 degree of
body temperature Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperatur ...
. In addition, the air is humidified, and dust and other particulate matter is removed by nasal hair in the nostrils. The entire mucosa of the nasal cavity is covered by a blanket of mucus, which lies superficial to the microscopic cilia and also filters inspired air. The cilia of the respiratory epithelium move the secreted mucus and particulate matter posteriorly towards the pharynx where it passes into the esophagus and is digested in the stomach. The nasal cavity also houses the sense of smell and contributes greatly to taste sensation through its posterior communication with the mouth via the choanae.


Clinical significance

Diseases of the nasal cavity include viral, bacterial and fungal infections, nasal cavity tumors, both benign and much more often malignant, as well as inflammations of the
nasal mucosa The nasal mucosa lines the nasal cavity. It is part of the respiratory mucosa, the mucous membrane lining the respiratory tract. The nasal mucosa is intimately adherent to the periosteum or perichondrium of the nasal conchae. It is continuous ...
. Many problems can affect the nose, including: * Deviated septum - a shifting of the wall that divides the nasal cavity into halves * Nasal polyps - soft growths that develop on the lining of the nose or sinuses * Nosebleeds * Rhinitis - inflammation of the nose and sinuses sometimes caused by allergies. The main symptom is a runny nose. * Nasal fractures, also known as a broken nose * Common cold * Sinonasal tumors


See also

*
Nasal irrigation Nasal irrigation (also called nasal lavage, nasal toilet, or nasal douche) is a personal hygiene practice in which the nasal cavity is washed to flush out mucus and debris from the nose and sinuses, in order to enhance nasal breathing. Nasal ir ...
*
Danger triangle of the face The danger triangle of the face consists of the area from the corners of the mouth to the bridge of the nose, including the nose and maxilla. Due to the special nature of the blood supply to the human nose and surrounding area, it is possible, ...


References


External links

* * Gross anatomy dissection of the nasal cavity, vide

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{{DEFAULTSORT:Nasal Cavity Nose Olfactory system Respiratory system Sensory organs