Final answer:
The bronchioles have a thicker layer of smooth muscle than the bronchi, and their contraction narrows the diameter of the bronchiole.
Step-by-step explanation:
True.
The bronchioles have a proportionately thicker layer of smooth muscle than the bronchi. Contraction of this smooth muscle narrows the diameter of the bronchiole, which is referred to as bronchoconstriction, not bronchodilation. Smooth muscle in the lungs helps regulate air flow through the airways, allowing them to expand and contract as necessary.