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Functions and Anatomy of Human Nasal Cavity

Smita Pandit
Separated by the nasal septum into right and left side, the nasal cavity is an air-filled space that is located above the oral cavity and is continuous with the nasopharynx (cavity forming the upper part of the throat). This post provides information on the anatomy and functions of the nasal cavity.

Did You Know?

The human nose has about 400 olfactory receptors. According to a recent study, the human nose can detect about a trillion odors, which is way higher than the previous estimate of 10,000 odors.
A sensory organ that is responsible for olfaction, the human nose is a part of the respiratory system. Comprising the external nose and nasal cavity, the nose is not only associated with olfaction, it also helps in conditioning the air that we inhale. The nasal bone and cartilage provide shape to the nose.
The external nose consists of a bony and cartilaginous framework. It is made of the frontal bone, nasal bones, maxilla bone, lateral cartilage, and alar cartilage. The nostrils, or anterior nares, are two external openings to the nasal cavity. Choanae, also called posterior naris, refer to 2 apertures of the nasal cavity that open into the nasopharynx.
It is the nasal septum that acts as a partition, dividing the nasal cavity into the right and left nasal cavities. Each of these cavities has a lateral wall, medial wall, roof, and floor. The nasal cavity is connected to the pharynx (throat) at the back.
The eye sockets lie lateral to the nasal cavities. Paranasal sinuses, which are four pairs of air-filled spaces in the bones of the skull, are the extensions of the nasal cavity.

Anatomy and Functions of the Nasal Cavity

The functions of the nose and nasal cavities are:
  • Respiration
  • Humidification of the inhaled air
  • Filtration of dust
  • Reception and drainage of secretions from the nasal mucosa, paranasal sinuses, and nasolacrimal ducts
  • Olfaction
After we inhale air, it flows into the area lying just inside the nostrils. This area is referred to as the vestibule. This is the only area that is not lined by mucous membrane. Lined by the epithelium and surrounded by cartilage, vestibule is involved with the filtering of dust from inhaled air.
Vibrissae, which are small hair present inside the vestibule help filter out the dust particles. Even the secretions of the sebaceous glands help in trapping dirt from the inhaled air. Lined by the respiratory mucosa, the respiratory region is the largest part of the nasal cavity.
On the surface of the respiratory mucosa is ciliated, pseudostratified columnar epithelium, which contains different types of cells. While the goblet cells secrete mucus, the ciliated cells perform the function of sweeping the dust and pathogens that are trapped in the mucus secreted by the goblet cells.
The underlying lamina propria contains a vast vascular network. The inhaled air becomes warm, as blood flows through the capillary loops that lie close to the surface. The nasal conchae provide large surface area, which allows the air to be warmed or humidified. Cilia are hair-like structures present in the respiratory epithelium.
These help move the particulate matter towards the throat, from where it travels through the esophagus to the stomach.

Nasal Cavity and Paranasal Sinuses

Both the nasal cavities comprise a floor, roof, lateral wall, and medial wall. The ethmoid bone contributes to the medial wall, lateral wall, as well as the roof of each of these cavities, whereas the floor is formed by palatine process of the upper jaw maxilla and the horizontal plate of the palatine bone. The cribriform plate of the ethmoid bone, nasal bones, frontal bone, and the posterior of the sphenoid bone contribute to the roof of the nasal cavity.
The medial wall is formed by the septum, which divides the nasal cavity into two sections. The nasal septum consists of bone, as well as cartilage. It is made up of the following:
  • Vomer and the perpendicular plate of the ethmoid bone, which form the upper part
  • Septal cartilage, which forms the anterior section
  • Crest of the maxillary bone and palatine bone which form the lower part
The nasal conchae, which are also called turbinates, are scroll-shaped bony projections that increase the respiratory surface area. They also cause turbulence in airflow, which in turn conditions the air that we inhale.
These are named conchae, as they are shaped like seashells. The superior, middle, and inferior turbinates are located laterally, with each turbinate located on either side of the nasal cavity. These extend towards the middle, and then move downwards into the nasal airways. The turbinates divide the nasal cavity into four air passages.
The space below each of the turbinates is referred to as a meatus.
  • Superior meatus, which lies below the superior concha, receives the opening of the posterior, anterior, and middle ethmoid sinus.
  • Middle meatus, which lies below the middle concha, receives the opening of the frontal sinus and maxillary sinus.

  • Inferior meatus, which lies below the inferior concha, receives the opening of the nasolacrimal duct.
The paranasal sinuses are connected to the nasal cavity through small orifices called ostia. Sphenoethmoidal recess is a small area above the superior concha that receives the opening of the sphenoid sinus.
Above the uppermost turbinate in both nasal cavities lies the olfactory region, which has a small area of about 2.5 cm2, and contains about 50 million specialized primary sensory receptor cells.

Arterial Supply

The nasal cavity is supplied by the branches of the maxillary artery, which in turn is one of the terminal branches of the external carotid artery. The sphenopalatine artery, which is also known as the artery of epistaxis, is one of the branches of the maxillary artery that passes through the sphenopalatine foramen into the nasal cavity.
At the rear section of the superior meatus, where it gives off posterior lateral nasal branches. After crossing under the sphenoid bone, the sphenopalatine artery ends on the posterior septal branches on the nasal septum. Thereafter, it joins or merges with the branches of the greater palatine artery.
It also joins the septal branch of the facial artery's superior labial branch in the region of the vestibule. The nose is also supplied by a branch of the ophthalmic artery called anterior ethmoidal artery.

Innervation and Olfaction

On the roof of the nostrils lies the nasal mucosa, which contains the olfactory epithelium. Millions of special olfactory receptor cells line the olfactory epithelium. The epithelium also contains the Bowman's glands that produce the secretion that bathes the surface of the receptor cells.
Hair-like structures called cilia hang freely from the ends of the cells into the mucous layer that lines the epithelium. The odor molecules attach themselves to the membrane receptors on the cilia.
The olfactory receptor neurons of the olfactory nerve extend from the olfactory epithelium to the olfactory bulb, which lies on the superior surface of the cribriform plate that lies above the nasal cavity. As the odorants bind to the receptors on the cilia, olfactory receptors generate electrochemical impulses.
Thereafter, the receptor axons carry the impulses through the holes in the cribriform plate to the olfactory bulb. The signals that are transmitted from the olfactory bulb travel to the amygdala and certain parts of the cerebral cortex. The signals are transmitted from the primary olfactory cortex to other parts of the brain.
Besides the olfactory nerve, the nasal cavities are supplied by ophthalmic (V1) division of the trigeminal nerve, which gives off the anterior and posterior ethmoidal nerves, and the maxillary (V2) branch of the trigeminal nerve, the largest one being sphenopalatine nerve that supplies sensation to the septum and the lateral wall.
Nasal secretions and mucus production is controlled by autonomic innervation from the brain to the vidian nerve, which then sends special parasympathetic fibers along with branches of the sphenopalatine nerve.
Likewise, blood flow to the nasal cavity and nasal mucosa is controlled largely by opposing sympathetic nerve fibers that also travel along with the sphenopalatine nerve. The nasal cavity is innervated by autonomic fibers. The sympathetic nerve fibers supply the blood vessels of the mucosa, which allows them to constrict.
The postganglionic parasympathetic nerve fibers that originate from the facial nerve control the secretion by the mucous glands.One of the major functions of the nasal cavity is that it warms and moistens the air that we inhale. Before the air reaches the lungs, dirt, irritants, and pathogens from the inhaled air are trapped by the mucus.
This lowers the risk of infections caused due to the exposure to environmental irritants and pathogens. The nasal cavity is also involved with the sneezing reflex. The excess mucus or secretions are swallowed, as the cilia propels it towards the pharynx.