INNERVATION OF THE LUNGS AND TRACHEOBRONCHIAL TREE
The tracheobronchial tree and lungs are innervated by the autonomic nervous system. Three types of pathways are involved: autonomic afferent, parasympathetic efferent, and sympathetic efferent. Each type of ﬁber is discussed here; the neurochemical control of respiration is covered later in the section on physiology (see Plates 2-25 and 2-26).
Autonomic Afferent Fibers
Afferent ﬁbers from stretch receptors in the alveoli and from irritant receptors in the airways travel via the pulmonary plexus (located around the tracheal bifurcation and hila of the lungs) to the vagus nerve. Similarly, ﬁbers from irritant receptors in the trachea and from cough receptors in the larynx reach the central nervous system via the vagus nerve. Chemoreceptors in the carotid and aortic bodies and pressor receptors in the carotid sinus and aortic arch also give rise to afferent autonomic ﬁbers. Whereas the ﬁbers from the carotid sinus and carotid body travel via the glossopharyngeal nerve, those from the aortic body and aortic arch travel via the vagus nerve. Other receptors in the nose and nasal sinuses give rise to afferent ﬁbers that form parts of the trigeminal and glossopharyngeal nerves. In addition, the respiratory centers are controlled to some extent by impulses from the hypothalamus and higher centers as well as from the reticular activating system.