Question

Each of these statements is true except one. Identify the exception.

A) Monoamine oxidase is the main enzyme responsible for the degradation of catecholamines.
B) β1 receptors respond equally well to both epinephrine and norepinephrine.
C) β2 receptors are not innervated by sympathetic neurons, so are more sensitive to epinephrine, delivered via the blood.
D) Activation of α receptors opens Na+ channels in the membrane.

Answer 1

The exception among the provided statements is the claim that activation of α receptors opens Na+ channels in the membrane, which is incorrect as α receptor activation affects intracellular second messengers rather than opening sodium channels directly(option d).

Step-by-step explanation:

Out of the statements provided by a student, the exception is that d)activation of α receptors opens Na+ channels in the membrane.

This statement is not accurate because the activation of α adrenergic receptors typically leads to changes in the levels of intracellular second messengers such as cAMP, and not directly to the opening of sodium channels. By contrast, beta-adrenergic receptors, when activated by catecholamines like epinephrine and norepinephrine, can lead to the opening of ion channels such as calcium and potassium channels, affecting heart rate and muscle relaxation respectively.

β1 receptors indeed respond to both epinephrine and norepinephrine, β2 receptors are primarily sensitive to epinephrine and are not innervated by sympathetic neurons, and monoamine oxidase is a key enzyme responsible for the degradation of catecholamines like dopamine, norepinephrine, and epinephrine.