Paranasal sinus

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The paranasal sinuses are eight (four pairs) air-filled spaces, or sinuses, within the bones of the skull and face. These are divided into subgroups that are named according to which bones they lie under;

the maxillary sinuses, also called the antra, are under the eyes, in the maxillary bones (cheek bones).
the frontal sinuses, over the eyes, in the frontal bone, which forms the hard part of the forehead.
the ethmoid sinuses, between the nose and the eyes, backwards into the skull.
the sphenoid sinuses, in the centre of the skull base.

Biological function

The sinuses probably fulfil a number of functions:

Decreasing the relative weight of the front of the skull, and especially the bones of the face. The shape of the facial bones is important, as a point of origin and insertion for the muscles of facial expression.
Increasing resonance of the voice
Providing a buffer against blows to the face
Insulating sensitive structures like dental roots and eyes from rapid temperature fluctuations in the nasal cavity.
Plays a minor role in humidifying and heating of inhaled air because of slow air turnover in this region.

Ailments

The paranasal sinuses are joined to the nasal cavity via small orifices called ostia. These become blocked relatively easily by allergic inflammation, or by swelling in the nasal lining which occurs with a cold. If this happens, normal drainage of mucus within the sinuses is disrupted, and sinusitis may occur.

These conditions may be treated by drugs such as pseudoephedrine, which reduce moisture in the sinuses, or by traditional techniques of nasal cleansing.

For more details on this topic, see Sinusitis.

Trivia

Sinus is a Latin word meaning a fold or pocket; in particular the front pocket in a toga.

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