The site of the defect in asthma. Neurohumoral, mediator or smooth muscle?

The nature of the underlying defect in asthma is still unclear. This article discusses where the primary problem might lie, starting with the assumption that it is likely to be in neurohumoral control, bronchial smooth muscle or cellular dysfunction with increased release of mediators. The weight of the evidence suggests that the latter is most likely. If true, the question of why this occurs still remains.