Structure and Anatomy of the Nose

The nose is an important organ performing vital functions in the human body related to smell (olfaction) and respiration. The nose also plays a role in the way we taste food, and this is the reason why food seems bland and unappetizing when our nose is congested.

The anatomy of the nose is split into two parts, the external part and the internal part of the nose. The external part refers to the portion of the nose that is visible externally on the face. Besides aesthetics, the external part protects the nasal cavity and admits air into the inner part of the nose. The internal part of the nasal anatomy is named the nasal cavity which is the first part of the upper respiratory tract. The structure of the nasal walls and nasal conchae is shaped by the 12 cranial bones.

Position and Structure of the Nose

The nares, also called the nostrils, open into the nose and constitute the primary route for entry of air into the human respiratory system. Posterior to each nostril there exists a wide cavity whose walls are shaped by various bones of the face. The nasal septum separates the right and left cavities of the nose. The nasal septum is a perpendicular plate of bone and cartilage, which is formed by the vomer and ethmoid bones and the cartilage that makes up the anterior part of the nose.

The External Nose

The external nose is pyramidal in shape. Positioned superiorly is the nasal root, which is continuous with the forehead. Inferiorly, the apex culminates in a rounded tip. Stretching between the root and the apex is the dorsum. Just inferior to the apex is found two pyriform openings, the nares, which form the entry into the nasal vestibule. The medial border of the nares is made up of the nasal septum and the lateral border is facilitated by the alae nasi ( lateral cartilaginous wings of the nose).

Skeletal Structure

The skeletal structure of the external nose is composed of two parts: the bony part and the cartilaginous part. 

• Bony aspects: Placed superiorly, it is made up of parts of the nasal bones, maxillae, and frontal bones
• Cartilaginous aspects: Placed inferiorly, it is made up of two lateral cartilages, two alar cartilages, and one septal cartilage
• Besides, there are some smaller alar cartilages on each side

The skin covering the bony part of the nose is thin, whereas that found over the cartilaginous part is thicker and possesses numerous sebaceous glands. The skin of the external nose extends up to the vestibule of the nose. At the nare, there are numerous hairs, whose role is to filter the air that enters the respiratory system.

The Internal Nasal Septum

The internal nasal septum divides the nasal cavity into two nostrils. The bones that make up the nasal septum can be divided into the following:

• Paired bones: Nasal, maxillary, and palatine bones
• Unpaired bones: Ethmoid and vomer bones

The central portion of the nasal septum is composed of the ethmoid, which is one of the most complex bones in the human body. The septal cartilage contributes the anterior portion and the posterior part is made up of the vomer.

The hard palate makes up the floor of the nasal cavity, thus, distinguishing it from the oral cavity. The hard palate is constituted posteriorly by the palatine bone, and anteriorly by the palatine process of the maxilla. The cribriform plate of the ethmoid makes up the roof of the nasal cavity.

Muscles of the External Nose

It is the muscles in the external nose that enable one to have facial expressions. Moreover, these muscles are responsible for the patency of the nostrils. The procerus muscle and the nasalis muscle are the muscles that play a prominent role in nasal anatomy. All the muscles here are innervated by branches of the facial nerve.

The procerus muscle has its origin in the fascia which overlies the nasal bone, and it inserts into the inferior forehead. Contraction of this muscle depresses the medial eyebrows and causes wrinkling of the skin present on the superior dorsum.

The nasalis is a sphincter-like muscle, whose transverse part supports the procerus. Concurrently, the alar part of the nasalis has its origin in the maxilla and is inserted into the major alar cartilage. Contraction of the nasalis distends the nostrils, causing them to flare.

Clinical Significance

Saddle Nose Deformity

This is seen primarily in cases of nasal trauma wherein septal support to the nose is affected, thus causing the middle portion of the nose to appear sunken.

The Nasal Cavity – A Significant Component of Nasal Anatomy

The nasal cavity which runs from the vestibule of the nose to the nasopharynx is divided into three components:

• Vestibule: This comprises the region encompassing the anterior external opening to the nasal cavity
• Respiratory component: This section is lined with ciliated pseudostratified epithelium combined with goblet cells which secrete mucus
• Olfactory component: This is the region at the apex
• Olfactory cells, which have olfactory receptors line this region

Nasal Conchae

There are curved shelves of bone that protrude from the lateral walls of the nasal cavity. These are known as conchae or turbinates. The conchae are three in number and are termed inferior, middle, and superior conchae. 

The conchae project into the cavity of the nose, thus, giving rise to four pathways that enable the flow of air. These groove-like passages, called meatuses, serve to increase the total surface area in the nasal cavity. They are:

• Inferior meatus: Seen bounded by the inferior concha and floor of the nasal cavity.
• Middle meatus: Present between the middle and inferior concha.
• Superior meatus: Between the superior and middle concha.
• Spheno-ethmoidal recess: Superiorly and posteriorly to the superior concha.

The conchae serve to increase the surface area of the nasal cavity, which consequently increases the extent of inspired air coming into contact with the walls of the cavity. Besides, they hinder the fast, laminar flow of air, causing it to become slow and turbulent. Air which enters the nose, is present in the nasal cavity for a longer time, in order to humidify it.

Openings in the Nasal Cavity

There are structures that drain into the nasal cavity, in order to facilitate drainage.

The paranasal sinuses open into the nasal cavity. The anterior, frontal, and maxillary ethmoidal sinuses drain into the middle meatus.

The middle ethmoidal sinuses drain onto what is known as an ethmoidal bulla, which is a bulge seen in the lateral wall of the ethmoidal sinus. The posterior ethmoidal sinuses have openings at the level of the superior meatus.

The sphenoid sinus opens onto the posterior roof and is thus the sole structure not draining onto the lateral walls of the nasal cavity. Other structures which drain into the nasal cavity include the nasolacrimal duct and the auditory tube.

• Nasolacrimal duct: It drains tears from the eye, opening into the inferior meatus
• Auditory tube: Also known as the Eustachian tube, this structure drains into the nasopharynx
• It enables the pressure in the middle ear to balance with atmospheric pressure

Paranasal Sinuses

The paranasal sinuses are composed of four groups of small cavities, which contain air, located in the bones of the cranium and face. These sinuses open into the cavity of the nose and in line with that of the nasal cavity, they are lined all around with ciliated pseudostratified epithelium mixed with mucus-secreting goblet cells.

Clinical Significance

Sinusitis

As seen in the anatomy of the nose, the paranasal sinuses are connected with the cavity of the nose. Hence, it is highly likely that infections in the upper respiratory tract can be transmitted to the sinuses. This leads to pain and swelling of the mucus layer. This infection is termed sinusitis. When more than one sinus is afflicted, the condition is termed pansinusitis. In most persons affected with sinusitis, the primary viral infection is most often followed by bacterial infection.

The maxillary sinus and maxillary teeth are both innervated by the maxillary nerve. Thus, it is not uncommon to find that inflammation of the maxillary sinus presents with a toothache.

Vasculature of the Parts of the Nose

The nose is able to significantly alter the temperature and humidity of the air that enters it. This is facilitated by its ample blood supply. Both external and internal carotid arteries supply blood to the nose.

Internal Carotid Branches

• Anterior ethmoidal artery
• Posterior ethmoidal artery

External Carotid Branches

• Sphenopalatine artery
• Greater palatine artery
• Superior labial artery
• Lateral nasal arteries
• Kiesselbach’s plexus (which is seen at the anterior—inferior part of the septum; this is the most typical cause for bleeding in cases of epistaxis.)

Besides the ample vasculature to the nose, the arteries here form anastomoses with each other. This is abundantly present in the anterior portion of the nose. In some persons, some nasal veins combine with the sagittal sinus. This forms a probable path for infection to spread from the nose into the cranial cavity.

Nerve Supply to the Nose

Three cranial nerves serve the nose. With regard to function, the innervation of the nose can be classified into two: general and special nerve supply.

• General innervation is provided by the nasopalatine and nasociliary nerves. The outer skin of the nose is served by the trigeminal nerve.
• The olfactory function of the nose is served by the special sensory innervation. This is performed by the olfactory nerves. The olfactory bulb is seen on the superior surface of the cribriform plate. Olfactory nerve branches pass through the cribriform plate providing a special sensory nerve supply to the nose.

Clinical Significance

Cribriform plate fracture

The cribriform plate can be fractured following trauma to the nose. This is critical as the fractured plate can pierce the meninges in the brain, leading to cerebrospinal fluid leakage. This kind of trauma exposes the brain to the external environment which in turn raises the risk of encephalitis, meningitis, and cerebral abscesses.

In some cases, a fracture of the cribriform plate can cause the olfactory bulb (situated on the cribriform plate) to be permanently damaged, which may lead to anosmia, the loss of smell.

Clinical Relevance of the Anatomy of the Nose

Congenital Conditions

• Choanal atresia: This condition can manifest unilaterally or bilaterally and presents with the obstruction of the posterior nasal aperture
• This congenital abnormality, if bilateral, will cause intermittent cyanosis and obstruction in the nose, after birth

Traumatic Conditions

• Epistaxis
• Nasal bone fracture
• Cribriform plate fracture

Neoplastic Conditions

• Nasal papilloma: These are benign epithelial tumours of the cavity of the nose, most often seen in the male population, 45-60 years of age
• These always need to be removed surgically
• Nasal polyp: These are non-cancerous protuberances of the mucus layer in the nose, typically seen around the maxillary sinuses
• Systemic glucocorticoids or resection can be used to manage this condition. However, recurrences are common

Conclusion

The external and internal parts of the nose compose the anatomy of the nose, thus enabling this organ to perform its primary functions of olfaction and respiration. Furthermore, the nose plays a relevant role in taste perception and speech, as well.