Bronchodilators work by relaxing the smooth muscles in the airways of the lungs, which helps to widen the air passages and improve breathing. They do this by stimulating beta-2 receptors in the lungs, which leads to the relaxation of the muscles and the opening of the airways. Bronchodilators are commonly used to treat respiratory conditions such as asthma, bronchitis, and emphysema, and may be administered through inhalers or nebulizers.