The bottom or floor surfaces of the nostrils tend to be more horizontal and the top or roof surfaces have been shaped more like an arch. A bony and cartilaginous septum separates your two nostrils. The several nasal sinuses, including the better-known frontal sinuses in the forehead above the eyes and the maxillary sinuses on each side of the nose, play various roles in breathing, thinking, illness and in yoga. Most of us realize their existence when they become infected, as with colds, hay fever, or noxious gases or dusts, resulting in headaches. Some sinuses appear to perform an important function in cooling the brain.
Nervous activity uses energy which seems to generate heat that needs to be conducted away.
Thus, somewhat like the radiator of an automobile, the sinuses may serve as a cooling system for the brain, which supplements the circulatory system wherein the blood serves as a coolant. Deep breathing and posture exercises not only increase oxygenation through the lungs and circulation of the blood within the brain, but also tend to enlarge and clear the sinus cavities for freer air circulation. The skin lining the nostrils consists primarily of membranes which do not dry out easily in the presence of moving air. They are kept moist by secretions called mucus which sometimes dries and hardens into a cake which must be expelled. Hairs embedded in such membranes, especially near the outer opening, often grow into sieve-like mats which catch and repel small objects, insects and dust.