(Functions of Nor-adrenalin)
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Norepinephrine, also called noradrenaline, substance that is released predominantly from the ends of sympathetic nerve fibres and that acts to increase the force of skeletal muscle contraction and the rate and force of contraction of the heart. The actions of norepinephrine are vital to the fight-or-flight response, whereby the body prepares to react to or retreat from an acute threat.Norepinephrine is classified structurally as a catecholamine—it contains a catechol group (a benzene ring with two hydroxyl groups) bound to an amine (nitrogen-containing) group. The addition of a methyl group to the amine group of norepinephrine results in the formation of epinephrine, the other major mediator of the flight-or-flight response. Relative to epinephrine, which is produced and stored primarily in the adrenal glands, norepinephrine is stored in small amounts in adrenal tissue. Its major site of storage and release are the neurons of the sympathetic nervous system (a branch of the autonomic nervous system). Thus, norepinephrine functions mainly as a neurotransmitter with some function as a hormone (being released into the bloodstream from the adrenal glands).