Both parasympathetic and sympathetic nerve fibres are provided by the lung.

Sympathetic fibres are originated from T2 to T5 spinal sections and The parasympathetic fibres are originated from the vagus nerve. Both provide motor to the bronchial muscles and secretomotor provide to the mucous glands of the bronchial tree.

The parasympathetic fibres cause bronchoconstriction/ bronchospasm, vasodilatation, and increased mucous secretion. The sympathetic fibres cause bronchodilatation, vasoconstriction, and reduced mucous secretion.

The afferent nerve impulse originating from the bronchial mucous membrane and stretch receptors in the alveolar walls pass to the central nervous system via both sympathetic and parasympathetic fibres.

Clinical Significance

Bronchial Asthma

It’s a common disease of the respiratory system. It happens because of bronchospasm (spasm of smooth muscle in the wall of bronchioles) which reduces the diameter of the bronchioles. Consequently, patient has great trouble during expiration, in spite of the fact that motivation is achieved normally. The airflow is further impeded because of presence of excessive mucous that the patient is not able to clear because an effective cough can’t be generated. Medically the asthma is distinguished by (a) trouble in breathing (dyspnea) and (b) wheezing. The sympathomimetic drugs like epinephrine cause vasodilatation and alleviate the bronchial asthma.


It’s a clinical illness, where bronchi and bronchioles are dilated forever as a consequence of chronic necrotizing infection. They become filled up with pus resulting in airway obstruction. The basal sections of the lower lobe are prone to this state.

Aspiration Pneumonia

In supine position, aspirated material normally enters into superior (apical section) of the lower lobe, particularly on the right side for it’s the most dependent section in this position. It results in collection of secretions which might obstruct the bronchus resulting in failure of the superior section of the lower lobe (atelectasis) and pneumonia.