Nasal cavity

Introduction

The nasal cavities are counted among the upper air conducting airways. It is formed by bony and cartilaginous structures. Besides the respiratory function, it is relevant for antibacterial defence, speech formation and olfactory function.

It is associated with various structures in the cranial region. The nasal cavity opens ventrally (anteriorly) via the two nostrils (nares). To the back, it passes over the choanae into the pharynx (throat).

It is limited by bones laterally (to the side), cranially (above) and caudally (below). The front part of the nasal cavity is called the nasal vestibule. It extends from the nostrils (nares) to an arch-shaped fold of mucous membrane, which represents the transition to the main nasal cavity (cavitas nasi propria).

The narrowest section (in the outer part of the nose) of the anterior nasal cavity lies at this mucosal fold (Limen nasi). The typical external shape of the nose is formed by the nasal cartilage and the bony root of the nose (Radix nasi). The nasal cartilage forms the bridge of the nose, the nasal septum (septum nasi) and the nostrils.

It consists of several cartilaginous parts. The cartilago alaris major (large wing cartilage) forms the border of the nostrils and the nostrils with the crus medial (between the nostrils/nasal bridge) and crus lateral (outside around the nostrils) – thus also the tip of the nose. The nostrils are additionally formed by the cartilagines alares minores (small wing cartilages).

The cartilago septi nasi forms the cartilaginous septum nasi (nasal septum), which divides the nasal atrium into two parts (a right and a left). The main nasal cavity begins at the nasal septum nasi. This is laterally (to the sides) limited by the conchae nasales (nasal conchae).

The conchae nasales are bone protuberances (bone lamellae) of various skull bones: Parts of the ethmoid bone (Os ethmoidale), the upper jaw (Os maxillaris), the palatine bone (Os palatinum) and the lacrimal bone (Os lacrimale). Between the conchae nasales, the nasal passages are located on the lateral nasal wall. They lead dorsally via the two choanas (funnels) into the throat.

The nasal passages themselves represent a mouth area for the passageways and paranasal sinuses. There are three nasal passages (meatus nasi): When the eye is watery, the tear fluid flows through a system of tear ducts into the lacrimal duct and finally into the nose via the meatus nasi inferioir. If the production of tears is low, the liquid evaporates after exiting the nasal passage.

In the case of increased tear production, e.g. when people cry heavily, they may feel like swallowing their tears. This is due to the fact that the nasal inferior or nasal meatus is located near the chouans, so that the tear fluid drains through them into the nasopharynx and thus into the throat. The nasal cavity is limited upwards by the nasal roof.

It is formed by parts of the sphenoid bone, the nasal bone, the ethmoid bone and the frontal bone. Here the nasal cavity is connected to the wing bone pit via the sphenopalatinum foramen (a bone opening). This is a bony depression between two protrusions of the upper jaw (Os maxillaris) and the wedge bone (Os sphenoidale).

Nerves and vessels responsible for supplying the nasal cavity pass through this foramen. At the bottom, the nasal cavity is limited by parts of the upper jaw, the intermaxillary bone and the palatal bone. This is where the incisive canalis lies – a bony channel that connects the nasal cavity with the oral cavity.

Nerves and vessels for supplying the palate pass through it. The middle nasal wall, the septum nasi (nasal septum), divides the nasal cavity into a left and right section. In the anterior part, the septum nasi is bifurcated with cartilage.

In the rear part, the septum nasi is bony. If the position of the nasal wall is uneven, one side of the nasal cavity may be so narrow that the airflow is obstructed. Surgical treatment may be necessary here.

  • The uppermost nasal passage (Meatus nasi superior) connects the nose with the sphenoidal sinus (Sinus spenoidalis); this is one of the paranasal sinuses. It also represents the mouth for the posterior ethmoid cells. These are air-filled bone cavities (pneumatocytes) in the skull.

    In addition, the human olfactory organ is located in the nasal superior orifice.

  • The middle nasal passage lies laterally and below the medial nasal concha. The other paranasal sinuses (frontal sinus and maxillary sinus) and the anterior and posterior ethmoid cells open out through it.
  • The lower nasal passage (Meatus nasi inferior) represents the connection to the lacrimal apparatus. The nasolacrimal duct (Durctus nasolacrimalis) enters here.