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A part of the respiratory tract, the nose is the protruding part of the face that sits at the centre. It bears nostrils through which we breathe and smell fragrances. Nose gets its shape by the ethmoid bone and the nasal spectrum. On an average, males have larger nose than females. The external part of the nose has the roots that are between the eyes the dorsum that runs down the middle and the apex, which is the nose tip. There are two openings, called nostrils that help us in inhaling and exhaling air. The nasal spectrum, consisting of cartilage and bones, divides the nostrils. The nostrils are surrounded by parts known as alae. The bony part of the nose is formed by the bony nasal spectrum, nasal bones as well as parts of maxillae, palatine and frontal bones. The cartilaginous portion of the bones is formed by two lateral cartilages, two alar cartilages and a special cartilage.
The Bone Anatomy
The paired nasal bones attach to the frontal bones in the upper portion of the nose; connects to the lacrimal bones in the above and side portions and joins the ascending processes of the maxilla in below and sides. The bony nasal spectrum is made of the perpendicular plate of the ethmoid bone. The vomer bone is located below and at the back and is responsible for partially forming the choanal opening into the nasopharynx, which is the upper portion of the pharynx that is continuous with the nasal passage.
The internal roof of the nose is formed by the horizontal and perforated cibriform plate through which the sensory filaments of the olfactory nerves pass. The nasal septum is made of quadrangular cartilage, vomer bone and few portions of the premaxilla and palatine bones. It extends from the nasal bones in the midline to the bony septum in the midline and then down along the bony floor.
The Nasal Cavity
The presence of nares serves as a gateway to the nasal cavities. It posteriorly opens into the nasopharynx through the choanae. The nasal cavity is lined with nasal mucosa, except the nasal vestibule which is lined with the skin. The mucosa over the superior one-third of the nasal cavity forms the olfactory area. In this, the olfactory epithelium contains receptors of the olfactory neurons which help in detecting smells. The olfactory tract also helps in transmitting sensory information.
There are walls within the nasal cavity, which have the following features:
- Roof: The roof of the naval cavity wall is divided into three parts: frontonasal, ethmodial and sphenodial. Each of these parts corresponds to the underlying bone, of the same name.
- Floor: The floor includes the palatine process of the maxilla and the horizontal plate of the palatine bone.
- Medial Wall: The medial wall is the nasal septum along with its surrounding bones.
- Lateral Wall: Each lateral nasal wall has three pairs of turbinates, consisting of small, thin and shell-form bones: the superior concha, the middle concha and the inferior concha. The turbinates divide the nasal cavity into four passages that finally opens to the paranasal sinuses.
The Paranasal Sinuses
These are air-filled cavities that are present in the sphenoid, ethmoid, maxilla and frontal bones. They have a mucosal membrane lining and have minute openings into the nasal cavity.
- Sphenoid sinus: Found in the sphenoid bone, each of the sinuses open into the sphenoethmoid recess.
- Ethmoid sinus: There are three types of ethmoid sinuses, namely anterior, middle and posterior, all of which are located in the ethmoid bone between the nose and the eye. The anterior sinus opens into the nasal cavity by means of the infuldibulum. The middle sinus opens into the ethmoidal bulla. The posterior sinus opens into the superior meatus.
- Maxilla sinus: This sinus is located in the maxilla body behind the cheek and above the premolar and molar teeth roots. Being a pyramid shape, it opens into the nasal cavity through the semilunar hiatus.
- Frontal sinus: The sinus is present in the frontal bone. Each of the sinuses is triangular in shape and runs above the medial end of the eyebrows and backwards to the orbit. Like the maxillary sinuses, they also open into the nasal cavity via semilunar hiatus.
Nerve Supply, Blood Supply and Drainage
The infratrochlear and the external nasal branches of the ophthalmic nerve as well as the infraorbital branch of the maxillary nerve are responsible for nerve supply to the external nose. Both of these nerves are a part of the trigeminal nerve (CN V). The olfactory nerves pass through the cribiform plate of the ethmoid bone.
The human nose being well vascularized with arteries and veins therefore gets sufficient blood supply. There is a two-fold principal of arterial blood-vessel supply to the nose: one which includes the branch of the anterior ethmoid artery, branch of the posterior ethmoid artery and branches from the internal carotid artery and the other which comprises of the branches from the external carotid artery, angular artery, superior labial artery, greater palatine artery and the sphenopalatine artery.
Branches of the ophthalmic and maxillary arteries supply blood to the external nose. The ala and the septum skin are supplied by the facial artery. The maxillary arteries bring blood to the walls of the nasal cavity and sinuses. Of all the arteries, the sphenopalatine artery is most important since it anastomoses with the superior labial artery branch. Venous blood is returned from the nasal cavity by veins accompanying the arteries. Internally, the lateral nasal wall is supplied with blood by the sphenopalatine artery.
The lymphatic system of the nasal cavity arises from the superficial mucosa and drains posteriorly to the retropharyngeal nodes at the back and anteriorly in front either to the upper deep cervical nodes in the neck or into the submandibular lymph nodes and vessels in the lower jaw. It can also drain into both the nodes and glands of the neck and the jaw.