There are three types of nerve fibers that connect the lungs to the autonomic nervous system. Autonomic afferent fibers travel to the vagus nerve via the pulmonary plexuses, originating in the airways and the lungs. They transmit information from stretch receptors. Parasympathetic efferent fibers are all contained in the vagus nerve. They carry motor impulses to the airways and lungs which cause bronchiolar muscle contraction, gland secretion, and vasodilatation. The third group are the sympathetic efferent fibers which relax bronchial muscles, inhibit glandular secretion, and cause vasoconstriction.

Sympathetic Efferent System

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Parasympathetic Efferents

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The walls of the bronchi and bronchioles are innervated by the autonomic nervous system. There are b2-adrenergic receptors in the bronchial epithelium and smooth muscle. The b2 receptors are responsible for bronchodilatation and secretion. The a1 adrenergic receptors, on the other hand inhibit secretion. VIP is another mediator that has been shown to cause vasodilatation.

Applied Anatomy

Bronchospasm classically seen in asthmatics is a failure of normal mechanisms to optimize air flow, and it is usually caused by bronchospastic behavior of the smooth muscle induced most commonly by allergens and exercise.

The nerves are not visible and their position in the chest is implied by their relationship to the other structures in the chest. For example the left recurrent laryngeal nerve curls around the left main stem bronchus. When the left atrium enlarges significantly, it can impinge on the left recurrent laryngeal nerve and cause hoarseness. The Pancoast tumor in the apex of the lung can affect the sympathetic system and result in Horner’s syndrome, with meiosis, anhidrosis, and hoarseness.

 

Contolling mechanisms

This is a photograph of an overhead telephone wire with a control box – reminiscent of our nervous system with its central controlling ganglion. Courtesy Ashley Davidoff MD 70030