Epinephrine is a hormone released from the adrenal gland of the body, most often in a stressful situation. it is known as the "fight-or-flight" hormone. one way that it causes a response in the body is to activate receptors on muscle cells.
where are these cellular receptors located?

the receptors that first reaction in this response are located in our neurosecretary cells, which located near the hypothalamus After our brain accessing the current situation, it will crate an order to every cells in our body as responce to our current situation. The brain will tell our body to produce adrenaln, which will result in increased heart rate and heightened focus