Question

Norepinephrine is a neurotransmitter in the sympathetic nervous system that triggers smooth muscle relaxation in airways but smooth muscle contractions in most other organs. How can this be?

A-Other chemicals mediate the smooth muscle contractions.
B-The effect of any neurotransmitter depends upon the receptor expressed in that tissue. Smooth muscle in the airways must express a different receptor than smooth muscle elsewhere in the body.
C-The parasympathetic nervous system overrides the effects of the sympathetic nervous system.
D-Skeletal muscles do not respond to norepinephrine.

Answer 1

Norepinephrine affects different smooth muscles in various ways because they express different types of receptors that respond distinctively to the neurotransmitter.

Step-by-step explanation:

The answer to why norepinephrine triggers smooth muscle relaxation in airways but smooth muscle contractions in most other organs is that the effect of any neurotransmitter depends upon the receptor expressed in that tissue. Smooth muscle in the airways expresses a different receptor than smooth muscle elsewhere in the body. The adrenergic receptors in the airways respond to norepinephrine by causing relaxation, which aids in breathing, especially during 'fight or flight' situations where oxygen demand increases. Conversely, smooth muscles in other parts of the body have different adrenergic receptors that induce contraction, enabling the body to direct blood flow to vital organs like the heart, muscles, and brain.

The effect of any neurotransmitter depends upon the receptor expressed in that tissue. Smooth muscle in the airways must express a different receptor than smooth muscle elsewhere in the body. This is why norepinephrine can trigger smooth muscle relaxation in airways but smooth muscle contractions in most other organs. The presence of different receptors allows for different responses to the same neurotransmitter.