Pharmacology: Neuronal control of the airways

Question 1

What is the dominant neuronal control of the airways?

Answer 1

Parasympathetic cholinergic transmission

Question 2

a) Where are the ganglia in the airways situated?
b) Which nerve carries pre-ganglionic fibres to these ganglia?
c) What to the post ganglionic fibres innervate?

Answer 2

a) They are situated in the walls of the bronchi and bronchioles
b) The vagus nerve
c) The bronchial smooth muscle and submucosal glands

Question 3

What is the effect of parasympathetic stimulation on the airways?

Answer 3

M3 receptors are stimulated.
This causes bronchial smooth muscle contraction and increased mucous secretion.
Collectively this causes increased airway resistance.

Question 4

There is a subtype of parasympathetic post-ganglionic fibres, which, when stimulated, result in bronchial smooth muscle relaxation. What are the names of the transmitters employed by these fibres?

Answer 4

Vasoactive intestinal peptide

Nitric oxide

Question 5

Describe the sympathetic innervation of the airways.

Answer 5

There is no sympathetic innervation of the bronchial smooth muscle.
There is, however, innervation of the smooth muscle and submucosal glands of the blood vessels.

Question 6

What is the effect of sympathetic stimulation on the airways?
Describe how this comes about.

Answer 6

1. Pre-ganglionic fibres release ACh which causes stimulation of nicotinic ACh receptors on chromaffin cells in the adrenal gland.
2. Adrenaline and Noradrenaline are released into the bloodstream by the adrenal glands.
3. Beta 2 receptors on bronchial smooth muscle are activated by adrenaline and this causes smooth muscle relaxation. There is also decreased mucous secretion and increased mucociliary clearance mediated by beta-2 receptors.
   The overall effect is decreased airway resistance.