so mucus secretions drain from the sinuses into the nasal cav-
ity. Membranes that are inﬂ amed and swollen because of nasal
infections or allergic reactions (sinusitis) may block this drain-
age, increasing pressure in a sinus and causing headache.
The sinuses reduce the weight of the skull. They also serve
as resonant chambers that affect the quality of the voice.
Recall from chapter 7 (pp. 208 and 212) that the
nasal sinuses) are air-F lled spaces in the
of the skull
(f g. 19.4)
. These spaces
open into the nasal cavity and are lined with mucous mem-
branes that are continuous with the lining of the nasal cavity,
Major structures associated with the respiratory tract in the head and neck.
Mucus movement in the respiratory tract. (
) Cilia move mucus and trapped particles from the nasal cavity to the pharynx.
) Micrograph of ciliated epithelium in the respiratory tract (275×).