Anatomy of the Nose and Sinuses
Nose and sinus anatomy:
The External Nose
The nose is the most prominent feature of the face and serves as the main gateway for air entering the respiratory system. Its upper portion is supported by two small bones called the nasal bones, which form the hard "bridge" you can feel between your eyes. Below these bones, the shape of the nose is maintained by several pieces of cartilage — flexible, firm tissue that gives the lower nose its structure and allows it to bend slightly without breaking. The tip, the nostrils, and the middle partition of the nose are all shaped by these cartilages. The two openings at the bottom of the nose, called the nostrils (or nares), are where air enters and exits.
The Nasal Cavity
Once air passes through the nostrils, it enters a surprisingly spacious chamber called the nasal cavity. This cavity is divided into two halves by a thin wall called the nasal septum, which is made of both bone and cartilage. In many people, this septum is not perfectly straight — a condition known as a deviated septum — which can sometimes make breathing through one side of the nose more difficult than the other.
Along the outer wall of each side of the nasal cavity, there are three bony shelves that curl downward like small scrolls. These are called turbinates (or conchae). They increase the surface area inside the nose, and they are covered with a moist, warm lining called mucosa. As air flows over and around the turbinates, it is warmed to body temperature, humidified, and filtered of dust and particles. This conditioning process is essential — it protects the delicate tissues of the lungs from cold, dry, or dirty air.
The nasal cavity also houses the olfactory region, a small patch of specialized nerve tissue high up in the roof of the nose. This is where the sense of smell originates. Odor molecules dissolve in the thin layer of mucus covering this region and stimulate nerve endings that send signals directly to the brain.
The Paranasal Sinuses
Connected to the nasal cavity are four pairs of air-filled spaces within the bones of the skull, known as the paranasal sinuses. Each pair is named after the bone in which it sits:
Maxillary sinuses: The largest pair, located in the cheekbones on either side of the nose. These are roughly the size and shape of a small walnut.
Frontal sinuses: Situated in the forehead, just above the eyebrows. These vary considerably in size from person to person, and in rare cases one or both may be absent entirely.
Ethmoid sinuses: A collection of small, honeycomb-like air cells located between the eyes, behind the bridge of the nose. Rather than being a single open cavity, these consist of many tiny interconnected chambers.
Sphenoid sinuses: The deepest sinuses, tucked behind the ethmoid sinuses in the sphenoid bone near the center of the skull, close to important structures like the pituitary gland and the optic nerves.
All of the sinuses are lined with the same type of moist mucosa found in the nasal cavity. This lining continuously produces a thin layer of mucus, which is swept by microscopic hair-like structures called cilia toward small drainage openings that connect each sinus to the nasal cavity. Most of these openings drain into a region on the side wall of the nose called the ostiomeatal complex, a critical crossroads where the maxillary, frontal, and anterior ethmoid sinuses all converge. When these narrow drainage pathways become blocked — by swelling from a cold, allergies, or other causes — mucus can accumulate in the sinuses, creating the pressure and pain commonly known as sinusitis.
The exact purpose of the sinuses is still debated, but they are thought to lighten the weight of the skull, add resonance to the voice, provide a cushion to protect the brain during facial trauma, and help humidify and warm inhaled air.