Possible functions of the sinus cavities include decreasing the relative weight of the front of the skull, increasing resonance of the voice, providing a buffer against facial trauma, insulating sensitive structures from rapid temperature fluctuations, and humidifying and heating inhaled air. Theorists also believe the sinus cavities provide defense against immunological threats and regulate intranasal and serum gas pressures
The sinus cavities are a connected system of hollow cavities in the skull. The maxillary sinuses are located in the cheekbones. The frontal sinuses are located in the low-center of the forehead. The ethmoid sinuses are between the eyes at the nasal bridge. The sphenoid sinuses are located in bones behind the nasal cavity. The maxillary sinuses are about 1 inch in width and are the largest in the skull. The other sinus cavities are much smaller.
The sinus cavities are lined with soft, pink tissue called mucosa. Typically, the sinuses are empty except for a thin layer of tissue called mucous membrane. The mucous membrane produces mucus and helps moisten the air during inhalation. The mucus traps dust and germs that are in the air. The sinuses drain into the nose through a small drainage pathway called the middle meatus.