The nose is composed of an observable exterior segment (external nose) and an internal segment within the skull known as the nasal cavity (internal nose). The external nose, visible on the face, consists of a framework of bone and hyaline cartilage enveloped in skin and muscle and lined with a mucous membrane. This structure is supported by the frontal bone, nasal bones, and maxillary bone and is supplemented by a cartilaginous framework comprising the septal nasal cartilage, lateral nasal cartilage, and alar cartilage. The flexibility of the external nose is due to its hyaline cartilage composition. The nostrils, or external nares, provide entrance to the nasal vestibules. The nose's interior structures perform three essential functions: conditioning the incoming air, sensing smells, and modifying the vibrations of speech as they echo through the large, resonating chambers, thereby contributing to our communication.
The nasal cavity, the internal nose, is a vast space in the skull's anterior aspect, inferior to the nasal bone and superior to the oral cavity, lined with muscle and mucous membrane. This cavity is divided into right and left sides by the nasal septum. Ducts from the paranasal sinuses and the nasolacrimal ducts open into the nasal cavity. The paranasal sinuses are hollow areas in specific cranial and facial bones that connect with the nasal cavity and produce mucus. The bones forming the internal nose's lateral walls are the ethmoid, maxillae, lacrimal, palatine, and inferior nasal conchae.
The nose's bony and cartilaginous structure ensures the unobstructed openness of the vestibule and nasal cavity. The nasal cavity is split into a larger, inferior respiratory region and a smaller, superior olfactory region. The respiratory region is lined with respiratory epithelium. Inhaled air first passes through the nasal vestibule, lined by skin containing coarse hairs that filter large dust particles. The conchae divide the nasal cavity into grooves, which increase the internal nose's surface area and prevent dehydration. The warmed, inhaled air circulates the conchae and meatuses, moistened by the mucus secreted by goblet cells. Dust particles are trapped in the mucus, which the cilia move toward the pharynx, allowing the particles to be swallowed or expelled. The olfactory epithelium in the respiratory region consists of olfactory receptor cells, supporting cells, and basal cells. It contains cilia but lacks goblet cells.
