The nose is a complex organ, performing several important roles, from managing the air we breathe to enabling our sense of smell. It continuously protects and processes the air entering our bodies.
Main Structures and Passageways
Air enters the nose through the nostrils. Just inside the nostrils lies the nasal vestibule, an initial chamber lined with coarse hairs (vibrissae). These hairs trap larger particles, preventing them from entering the respiratory system.
Beyond the vestibule, air flows into the nasal cavity, a large, air-filled space extending towards the back of the throat. This cavity is divided into two halves by the nasal septum, a wall composed of both bone and cartilage. The septum ensures that air pathways remain separate, contributing to efficient airflow.
How the Nose Prepares Air
The nasal cavity is equipped with specialized structures that condition inhaled air for the lungs. Curved bony shelves called nasal turbinates increase the internal surface area. These turbinates create turbulence in the airflow, ensuring that incoming air makes extensive contact with the lining.
The nasal cavity is covered by a mucous membrane that produces sticky mucus. This mucus traps dust, pollen, other airborne particles, and pathogens, preventing them from reaching the lungs.
Tiny, hair-like projections called cilia, on the mucous membrane, constantly sweep this mucus and trapped particles towards the throat for swallowing or expulsion. This continuous sweeping action, known as mucociliary clearance, is a primary respiratory defense mechanism.
The turbinates, mucous membrane, and cilia also warm and humidify inspired air, making it more suitable for the lungs.
The Sense of Smell
The nose’s distinct functions include the sense of smell. Specialized nerve cells called olfactory receptors are located in the upper region of the nasal cavity.
These receptors have fine, hair-like extensions sensitive to chemical odor molecules in the air. When odor molecules bind to these receptors, they trigger electrical signals.
These signals are then transmitted along nerve fibers to the olfactory bulb, a structure located in the forebrain just above the nose. The olfactory bulb processes these signals before relaying them to other brain regions, where they are interpreted as specific smells.
Connected Air Pockets
The nasal cavity is connected to several air-filled spaces within the bones of the skull, known as the paranasal sinuses. There are four main pairs:
Frontal sinuses in the forehead.
Maxillary sinuses below the eyes.
Ethmoid sinuses between the eyes.
Sphenoid sinuses located behind the eyes.
These sinuses are lined with a mucous membrane similar to that of the nasal cavity and drain mucus into it. While their exact functions are debated, they are thought to lighten the skull’s weight and resonate sound, influencing voice quality.