6.3 Additional neuronal control

The lungs also receive innervation from the autonomic nervous system (Figure 17). The sympathetic innervation originates from the thoracic portion of the spinal cord and synapses onto the bronchiolar smooth muscle. Stimulation of these nerves causes bronchodilation.

In parallel, the vagus nerves (or cranial nerve X) synapse onto the bronchi and pulmonary blood vessels as part of the parasympathetic innervation. Activity of these neurons counterbalances the sympathetic response by stimulating constriction of the bronchi. Activation of these pathways is involved in the ‘fight or flight’ response.

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Figure 17 Innervation of the lungs by the autonomic nervous system.

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On the left and on the right are drawings of a sagittal section of the brain and upper spinal cord. In the centre is a drawing of the lungs with trachea and bronchi / bronchioles.

Sensory neurons from the trachea pass to the T1 segment of the spinal cord (shown in blue on the left-hand diagram). Sensory neurons from the lungs pass, via the pulmonary plexus, to segments T2, T3 and T4 of the spinal cord (all shown in blue, as are the cell bodies of the sensory neurons outside of the spinal cord).

Motor neurons (shown as purple lines) from centres (shown as a purple dot) at the base of the medulla oblongata (shown in the right-hand diagram) pass to the lungs – these form fibres in the vagus nerve (cranial nerve X).

Figure 17 Innervation of the lungs by the autonomic nervous system.

Finally, if you play a musical wind instrument, you know that some aspects of breathing can be controlled voluntarily. This ‘override’ of the autonomic breathing system involves the motor cortex, thalamus and cerebellum, which are also involved in breath control during speech and behavioural tasks that modify breathing by learning and experience.