Final answer:
The pathway of bronchial smooth muscle constriction or dilation is controlled by the autonomic nervous system, with the parasympathetic system causing constriction and the sympathetic system inducing dilation. These processes regulate airflow in the lungs and are crucial for normal respiration.
Step-by-step explanation:
The bronchus is a tube connected to the trachea that branches into many subsidiaries and provides a passageway for air to enter and leave the lungs. The bronchus and its subdivisions, the bronchi and bronchioles, have walls that contain smooth muscle which helps regulate airflow.
Bronchial smooth muscle undergoes bronchoconstriction, a decrease in the size of the bronchiole due to the contraction of the muscular wall. Constriction is primarily induced by the parasympathetic nervous system and can also be a response to irritants, allergic reactions, or asthma-related stimuli. Alternatively, bronchodilation is an increase in the size of the bronchiole due to relaxation of the muscular wall and is stimulated by the sympathetic nervous system. This process is vital for adjusting the flow of air to the lungs as needed.
During conditions such as asthma, excess bronchoconstriction can lead to difficulty in breathing as the airways become overly narrowed, obstructing airflow.