The characteristics of the cell membrane that determines what gets into a cell and what doesn't is the properties of the phospholipid bilayer and its proteins.
Norepinephrine. Intuitively, it is also called noradrenaline. The neural transmitter acts on noradrenergic receptors. Adrenal glands release the neurotransmitter into the bloodstream and is used in the sympathetic nervous system. The neurotransmitter is significant in the fight-or-flight response to stimuli.
