The nasal cavity is the inside of the nose and is the most cephalic part of the respiratory tract. It is lined with a mucous membrane that helps keep the nose moist by making mucus so that nosebleeds from a dry nose can be prevented. The nasal cavity has four functions: warming and humidifying the inspired air, removing and trapping pathogens and particulate matter from the inspired air, responsible for the sense of smell, and draining and clearing the paranasal sinuses and lacrimal ducts. The nasal cavity is divided into two separate cavities by the septum and kept patent by a bone and cartilaginous framework. Each cavity consists of a roof, floor, medial wall, and lateral wall. Within each cavity are three regions: nasal vestibule, respiratory region, and olfactory region. The nasal cavity has an abundant supply of vasculature to aid in functions of warming and humidifying inhaled air. It allows the mucosa to enlarge and shrink, under the influence of sympathetic innervation. The nasal cavity is surrounded by air-containing mucosal lined sinuses, which include the frontal, paired maxillary, sphenoid, and ethmoid sinuses, and these cavities directly communicate with the nasal cavity.