The respiratory region is the largest part of the nasal cavity, has a rich neurovascular supply, and is lined by respiratory epithelium composed mainly of ciliated and mucous cells.
The olfactory region is small, is at the apex of each nasal cavity, is lined by olfactory epithelium, and contains the olfactory receptors.
In addition to housing receptors for the sense of smell (olfaction), the nasal cavities adjust the temperature and humidity of respired air by the action of a rich blood supply, and trap and remove particulate matter from the airway by filtering the air through hair in the vestibule and by capturing foreign material in abundant mucus. The mucus normally is moved posteriorly by cilia on epithelial cells in the nasal cavities and is swallowed.
Innervation of the nasal cavities is by three cranial nerves:
Olfaction is carried by the olfactory nerve [I].
General sensation is carried by the trigeminal nerve [V], the anterior region by the ophthalmic nerve [V1], and the posterior region by the maxillary nerve [V2].
All glands are innervated by parasympathetic fibers in the facial nerve [VII] (greater petrosal nerve), which join branches of the maxillary nerve [V2] in the pterygopalatine fossa.
Sympathetic fibers are ultimately derived from the
T1 spinal cord level. They synapse mainly in the superior cervical sympathetic ganglion, and postganglionic fibers reach the nasal cavities along blood vessels, or by joining branches of the maxillary nerve [V2] in the pterygopalatine fossa.
Blood supply to the nasal cavities is by: terminal branches of the maxillary and facial arteries, which originate from the external carotid artery, and ethmoidal branches of the ophthalmic artery, which originates from the internal carotid artery.
Bones that contribute to the skeletal framework of the nasal cavities include: the unpaired ethmoid, sphenoid, frontal, and vomer bones, and the paired nasal, maxillary, palatine, and lacrimal bones and inferior conchae.
Of all the bones associated with the nasal cavities, the ethmoid is a key element.
The single ethmoid bone is one of the most complex bones in the skull. It contributes to the roof, lateral wall, and medial wall of both nasal cavities, and contains the ethmoidal cells (ethmoidal sinuses).
The ethmoid bone is cuboidal in overall shape (Fig. 8.233A) and is composed of two rectangular box- shaped ethmoidal labyrinths, one on each side, united superiorly across the midline by a perforated sheet of bone (the cribriform plate). A second sheet of bone (the perpendicular plate) descends vertically in the median sagittal plane from the cribriform plate to form part of the nasal septum.
Each ethmoidal labyrinth is composed of two delicate sheets of bone, which sandwich between them the ethmoidal cells.
The lateral sheet of bone (the orbital plate) is flat and forms part of the medial wall of the orbit.
The medial sheet of bone forms the upper part of the lateral wall of the nasal cavity and is characterized by two processes and a swelling (Fig. 8.233B)—the two processes are curved shelves of bone (the superior and middle conchae), which project across the nasal cavity and curve downward ending in free medial margins, while inferior to the origin of the middle concha, the middle ethmoidal cells form a prominent bulge (the ethmoidal bulla), on the medial wall of the labyrinth.