Which of the following can impair or inhibit ciliary activity? 1. Drying of the respiratory tract mucosa 2. Exposure to smoke 3. Parasympatholytic drugs

a. 1 and 2 only
b. 1 only
c. 1, 2, and 3
d. 2 and 3 only

ANS: C
Ciliary beating can be effectively slowed or even stopped if the viscosity of the sol layer is in-creased by exposure to dry gas. Ciliary motion is also stopped following exposure to smoke, high concentrations of inhaled O2, and drugs like atropine.