The nose is one of the primary sensory organs responsible for the sense of smell; it also plays a vital role in breathing and speech production.
The nasal cavity is located just behind the two nostrils and forms the inside of the nose.
It constitutes the upper respiratory system and the paranasal sinuses, oral cavity, pharynx, and larynx and is the first of the respiratory tract structures.
Anatomy and physiology
The nasal cavity heats and humidifies the inspired air and filters small particles into the air before the air reaches the lung. The nasal cavity is lined with the same columnar epithelium that lines the lung’s airways.
This epithelium secretes a mucinous substance that lines the walls, helping the mucociliary eliminate small particles trapped in the mucosal surface.
The nasal cavity also provides drainage for the secretions of the paranasal sinuses and traps the particles carrying odors for smell in the olfactory voids.
The olfactory gaps are located in the upper part of the nasal cavity, medial to the superior turbinates.
The nasal cavity is surrounded by air-borne mucous-lined holes called paranasal sinuses, including the combined maxillary, frontal, ethmoidal, and sphenoidal sinuses.
The sinuses communicate directly with the nasal cavity. The walls of the sinuses secrete mucinous material.
They are covered by cilia that sweep the mucinous carpet and secretions with particles trapped in a defined path. The floor of the nasal cavity is the hard palate.
The lateral walls contain spiral-shaped mucosal folds that line the concha-shaped bone called turbinates and several sinus drainage holes.
The spiral nature or curve of the turbinates increases the surface and the contact with the inspired air. The roof is composed of the fibrous plate in the middle and the floors of the ethmoidal cells on each side.
The nasal cavity is separated by the partially bony and cartilaginous nasal septum. Unlike the lateral walls, the septum is lined by squamous epithelium.
In a study of computed tomography of the nasal cavity in children aged 0-3 years, with subjects divided into five age groups, it was found that the children did not show statistically significant differences in the distances between the skeletal or mucous structures of the cavity.
Such differences, however, were significant among children in groups with the most remarkable age differences. The study included 180 children examined by multislice computed tomography, with 18 measured distances within the nasal cavity.
The results were designed to help provide reference values for the diagnosis of nasal cavity stenosis in young children.
The frontal, maxillary, ethmoidal, and sphenoidal paired sinuses surround the nasal cavity. The ethmoidal sinuses form the roof, and the maxillary sinuses include the walls.
The frontal sinuses are anterior and superior to the ethmoid sinuses, and the sphenoid sinuses are posterior and superior to the ethmoid sinuses.
The main draining Ostia is the anterior ostiometatal complexes, which drain the bilateral frontal and maxillary sinuses and the anterior and middle third of the ethmoid sinuses.
The superior anterior wall is composed of cartilage. The upper posterior wall contains the perpendicular plate of the ethmoid bone, and the lower wall has the vomer and the nasal crests of the maxilla, and the bones of the palate.
The bony portion of the septum is often pneumatized; when overexpanded, it can deteriorate the flow of air in the bilateral sphenoid orifices in the sphenoethmoid recess.
The spurs and deviation of the septum can significantly affect the flow of air if the spur or deviated septum compresses the mucosa of the turbinate or the lateral wall of the nasal cavity. Severe nasal septum deviation can obstruct the respiratory tract and compress the turbinates.
The anatomy of the lateral wall of the nasal cavity is quite complex and is where most of the anatomical anomalies occur. People generally have three turbinates with upper, middle, and lower walls.
Some people have a fourth corner, the top corner. The space between the turbinates along its lateral margin and the lateral walls of the nasal cavity is known as the meatus.
The inferior turbinate is attached to the lateral wall of the nasal cavity, and only the nasolacrimal duct drains into the inferior meatus. Most of the flow of inspired air travels through the middle meatus instead of through the lower meatus.
The middle meatus is the most important because the maxillary sinuses, the last two-thirds of the ethmoid sinuses, and the frontal sinuses drain into it. Most anatomical variants occur in the middle meatus and the turbinate region.
The posterior third of the ethmoid and sphenoid sinuses drain into the superior meatus.
It is one of the most crucial bone structures; the uncinate process acts as a shield of ventilation, which prevents the direct inspiration of the air in the maxillary sinus and protects the exit of the mucociliary space.
The allergic rhinitis single or even viral and anatomical variations of the uncinate may reduce the ethmoid infundibulum, resulting in obstruction of normal sinus drainage.
This bone structure is fundamental for functional sinus endoscopic surgery because it is the first structure that is identified and surgically removed.
The uncinate process arises from the lateral wall and occasionally the inferior turbinate and projects towards the airway of the nasal cavity.
Its upper margin is attached to the floor of the anterior ethmoidal sinuses. It then decreases in height towards the nasopharynx, with its upper free edge forming the semilunar hiatus that opens directly towards the middle meatus.
The orbital floor or the medial wall is lateral to the uncinate process, with the ethmoid infundibulum between them, directly draining the maxillary sinus through the anterior, medial, and superior corners.
Several ethmoid air cells in the anterior two-thirds also drain into the infundibulum, as do the frontal sinuses.
The frontal recess or the drainage duct drains towards the anterior ethmoidal part of the middle meatus. Overexpansion of agger nasi cells, the ethmoid aerial cells located earlier, can compress this drainage channel.
Therefore, the bilateral frontal and maxillary sinuses and the anterior two-thirds of the ethmoid sinuses drain into the ethmoidal infundibulum.
Where is the Nasal Cavity Found?
The nasal cavity begins at the base of the skull and is separated from the oral cavity below the hard palate (roof of the mouth).
Portal: The area just behind the nostrils is the part of the nasal cavity most exposed to environmental threats.
Then, this part is filled with multiple layers of the same cells that form our skin (stratified squamous epithelium), creating a protective barrier.
This area also has stiff hairs on the nose (vibrissae) embedded in the cell lining and covered by thick mucus.
Respiratory region: begins at the end of the vestibular area and includes the entire nasal cavity and the olfactory region.
This region has a ciliated pseudostratified epithelium lining (single-cell layer) containing goblet cells that secrete mucus-forming the mucous membrane.
The olfactory region is the upper part of the nasal cavity near the septum, full of olfactory cells and olfactory mucosa. The mucosa hosts numerous cilia, which contain olfactory receptor proteins responsible for the sense of smell.
Walls and Limits of the Nasal Cavity
Medial wall: refers to the septum that divides the nasal cavity into two equal sections. The upper and lower bony parts of the septum are formed by the perpendicular plate of the ethmoidal bone and the vomer.
The lower frontal part is formed by a quadrangular cartilaginous hyaline structure known as septa cartilage. The lower part of the smooth medial wall can be seen outside, dividing both nostrils.
Upper edge (roof):
- The two nasal bones
- The lower part of the frontal bone
- The cribriform plate (ethmoidal bone)
- The sphenoidal bone forms the roof
Anterior edge (lateral wall): the lower parts of the nasal bones, the cartilage attached to them, the external nose, and the nasal passages are in the front part of the nasal cavity.
Posterior edge (posterior wall): the upper part of the back and sides are surrounded by a series of cranial bones that include the maxilla, the ethmoidal bone, the palatal bone, the sphenoid, and the lacrimal bone, as well as the inferior shell.
Soil: in addition to maintaining the nasal cavity separated from the oral cavity, the hard palate, formed by the maxilla (palatal process) and palatal bones (horizontal plates), also includes its smooth floor.
The nasal and oral cavities are connected through the nasopharynx in the back of the throat.
The soft palate and the uvula (a fleshy lump in the back of the throat) move up together to close this connection during the meal to prevent food from entering the nasal cavity.
Bones of the Nasal Cavity: The Three Nasal Cornets
Unlike the medial wall and the floor of the nasal cavity, the lateral wall has small bony projections that give it an irregular surface.
The three nasal turbinates create these projections. The upper nasal concave and the middle project from the ethmoidal labyrinth (part of the ethmoid bone), while the lower nasal concha is an individual bone structure.
They help to divide the breathing space inside the cavity in the tripe of the tree and allow the inhaled air to interact better with the different parts of the hole.
Breast Openings in the Nasal Cavity
Some spaces full of air with mucus between the bones of the face and skull help keep the headlight and play vital roles in breathing and speech.
Four sets of breasts have been recognized; frontal, sphenoid, ethmoid, and maxilla, all with an opening in the nasal cavity.
The anterior ethmoidal sinuses and the frontal and maxillary sinuses drain into the middle meatus, the opening marked with a growing groove, called the lunate hiatus, in the cavity’s lateral wall.
The middle ethmoidal sinuses form a bulge, the ethmoidal bulla, in the lateral walls and drain into it. The posterior ethmoidal sinuses drain near the superior meatus. The only remaining one, the sphenoid sinus, empties into the rear roof of the cavity.
Other Structures Drain in the Nasal Cavity
The tear duct (nasolacrimal duct) drains the tears in the nasal cavity, which leaves the eyes open to the inferior meatus. The auditory tube ( eustachian tube ) also opens near the lower meatus.
The rich vasculature of the nasal cavity helps control the temperature and humidity of the inhaled air. The branches of the internal carotid artery and the external carotid artery are responsible for the blood supply in this area.
The three primary sources of arterial supply are the ophthalmic, maxillary, and facial arteries. Smaller branches, including the anterior and posterior ethmoidal arteries, the sphenopalatine, the greater palatal, and the superior labial arteries, correspond to the three anterior components.
The facial and ophthalmic veins are responsible for the venous drainage of the external nose.
The innervation in this region can be divided into two parts: unique innervation (olfactory) and general innervation.
The first cranial nerve, the olfactory nerve, is responsible for the sense of smell and the branches of the brain’s olfactory bulb.
General innervation refers to the connection of the nerve with the nasal septum and the lateral walls, which are administered by the maxillary nerve branches (nasopalatine nerve) and the ophthalmic nerve branches (nasociliary nerve).
The trigeminal nerve provides innervation to the outside of the nose.
What does the Nasal Cavity do?
Function in the Respiratory System
The nasal cavity and its mucosa have two primary purposes in the breathing process:
Passage for inhaled air: During inhalation, air enters through the nostrils and passes through the nasal cavity to the pharynx and larynx, the following sections in the respiratory tract, to eventually reach the lungs.
The exhaled air travels reversely and leaves the body through the nasal cavity.
The mucosal membrane in the air purification: the thick mucous membrane, together with the vibrissae present in the inner walls of the nasal cavity, purifies the inhaled air trapping any dust, bacteria, and foreign particles in it, allowing only clean air to enter. Body.
The small projections in the form of hairs, or cilia, work to move the particles of dust trapped by the mucous membrane towards the back of the throat, where they can be swallowed, or towards the nose, where they can be eliminated when sneezing or blowing.
It also humidifies and heats the inhaled air to control the nature and temperature of the air entering the respiratory tract. It absorbs heat and moisture from the air during exhalation when it leaves the body.
Function as a Sensory Organ
A recent study states that a human nose can recognize about 1 billion different odors.
The olfactory mucosa contains around ten million olfactory cells, each with 350 types of odor receptors. These 350 receivers are each characteristic of a different kind of odor.
A small part goes to the olfactory area when the air enters the nasal passage. The receptors transport odorants present in the mood to specific neurons to take them to the olfactory bulb in the forebrain, where they are identified as different odors.
Function in Speech
It is an integral part of the vocal tract, with the oral cavity, pharynx, and larynx being the other organs involved in sound production.
For speech production, the larynx and the nasal and oral cavities modify the airflow, depending on the type of sound produced.
For a nasal consonant (nasal sound), the air is sent to pass through the nasal cavity, while for an oral consonant (oral sound), the air has to escape through the oral cavity.
Conditions Associated with the Nasal Cavity
Cancer: a relatively rare form of cancer that affects the nasal cavity and sinuses, can occur due to heavy exposure to toxic gases, excessive smoking, or old age.
Certain strains of human papillomavirus are also thought to be responsible in some cases.
Symptoms include nasal obstruction, nosebleeds, discharge of pus, reduced sensitivity to smell, formation of lumps or sores inside the nose, and pain around the eyes or upper teeth.
Standard treatment methods include chemotherapy, radiation therapy, and surgery to remove the tumor.
Nasal polyps: Sometimes, there are small, benign growths that grow in the nasal cavity or linings of the sinuses, often due to chronic inflammation caused by allergies, infections, chronic asthma, or immune disorders.
Usually, they do not cause any problems. Still, if the polyps grow, one may experience nasal congestion, runny nose, sneezing, taste and smell issues, frequent infections, and facial pain and itching.
Rhinitis: swelling and inflammation of the mucous lining of the nasal cavity; rhinitis can be classified as allergic and non-allergic, depending on its causative factors. The first occurs due to pollen, dust, pets, etc.
The non-allergic form can result from some viral infection, environmental changes, or even hormonal imbalances that cause accumulation of mucus and fluid in the nasal tissues and swelling of the blood vessels.
Symptoms include stuffy nose, irritation, burning sensation, runny nose / dry nose, and sneezing that may go away on their own or may need medication and nasal sprays.
Sinus infection: A viral, bacterial, or fungal condition is characterized by a swollen and inflamed nasal cavity. Also known as sinus headache or sinusitis, it causes pain and pressure in and around the sinuses, forehead, eyes, and teeth.
The treatment depends on the cause of the infection.