Final answer:
Methylxanthines induce bronchodilation by inhibiting the cellular enzyme phosphodiesterase, increasing levels of cAMP and reducing bronchial smooth muscle tone. The autonomic nervous system, including the sympathetic and parasympathetic systems also play a big role in the control of bronchial tone.
Step-by-step explanation:
The methylxanthines, a group of medications often used in the treatment of respiratory conditions such as asthma and chronic obstructive pulmonary disease, bring about bronchodilation - the widening of the bronchi to increase air volume in the lungs - by inhibiting a cellular enzyme called phosphodiesterase. This enzyme is involved in the breakdown of cyclic adenosine monophosphate (cAMP), an important signaling molecule in many biological processes including the regulation of bronchomotor tone. By inhibiting phosphodiesterase, methylxanthines increase the concentration of cAMP, which ultimately leads to a decrease in bronchial smooth muscle tone and hence bronchodilation.
Control of bronchial tone is also under the influence of the autonomic nervous system. The sympathetic nervous system, when activated, stimulates bronchodilation while the parasympathetic system promotes bronchoconstriction.