Parasympathetic innervation from the vagus nerve causes the airways to:

• A. remain unchanged
• B. constrict
• C. dilate
• D. become inflamed

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the role of the parasympathetic nervous system. The parasympathetic division of the autonomic nervous system is responsible for 'rest and digest' functions, which include conserving energy and promoting maintenance activities in the body.
2. Step 2: Recognize the function of the vagus nerve. The vagus nerve (cranial nerve X) is a major component of the parasympathetic nervous system and provides innervation to various organs, including the lungs and airways.
3. Step 3: Learn how parasympathetic stimulation affects the airways. Parasympathetic activation via the vagus nerve releases acetylcholine, which binds to muscarinic receptors in the smooth muscle of the airways, causing bronchoconstriction (narrowing of the airways).
4. Step 4: Eliminate incorrect options based on physiological knowledge. 'Dilate' is incorrect because dilation is typically associated with sympathetic activation. 'Remain unchanged' is incorrect because parasympathetic stimulation actively affects the airways. 'Become inflamed' is incorrect because inflammation is not directly caused by parasympathetic innervation.
5. Step 5: Conclude that the correct answer is 'constrict,' as parasympathetic innervation from the vagus nerve leads to bronchoconstriction of the airways.