Answer:
The correct option is : a. causing threshold to be reached more quickly
Explanation:
Norepinephrine, also known as noradrenalin, is an organic compound, which belongs to the catecholamine family. It acts as a hormone and a neurotransmitter in the brain and the body and also impacts the heart.
It is one of the hormones secreted by the adrenal medulla. Norepinephrine is a part of the fight-or-flight mechanism of the body. It acts by binding to the β-1 receptors and opens the chemical or ligand gated calcium and sodium ion channels. Therefore, <u>it causes the threshold to be reached faster </u>by increasing the rate of depolarization and thus causes heart arrhythmia.
Therefore, <u>Norepinephrine acts on the heart by </u><u>causing threshold to be reached faster.</u>
