Your sympathetic nervous system controls adrenaline production, and it’s part of your body’s network-wide fight or flight response; the conscious mind detects a threat, and the subconscious sympathetic nervous system responds – ready for battle. The sympathetic nervous system alerts your whole body through nerve pathways, sending signals racing along the nerves of cells in the adrenal medulla that secrete adrenaline and norepinephrine.
Your body produces adrenaline in response to an immediate and threatening physical encounter, sending signals that you’re in danger throughout your entire body. Adrenaline is a big deal because human beings have learned to stimulate its production with their mind without being in actual physical danger. Both fear of the future and fear of a charging tiger can cue adrenaline production.
Adrenaline has a similar effect on the body as the sympathetic nervous system, but it’s much farther reaching. The sympathetic nervous system helps control body-wide functions, such as arterial pressure or sweating, but it affects only a small portion of cells in the body. Alternatively, adrenaline can affect the metabolic rate of every cell in your body. Its (along with norepinephrine’s) effects can last five to ten times as long as sympathetic nerve stimulation.
Take, for example, a day at work. You’re sitting in front of your trusty computer, chaffing under the pressure of a stressful day, when your body responds by releasing adrenaline. Your sympathetic nervous system detects a “threat” and starts to send adrenaline coursing through your body. But you don’t run, and you don’t fight. You need to “burn off” the adrenaline; otherwise, you will stay in a state of hypervigilance. You could scream, jump up and down, or put your fist through the wall, but none of those responses are socially acceptable. So, instead, you grit your teeth, clench your fists, or even give yourself a stomachache. You continue to work.
Many of us often wonder why we’re so tired when we haven’t done much physical work or exercise by the end of the workday. How can sitting at a desk all day be so tiring? Now, you know! It’s not just in your head – your body was working hard, pumping adrenaline and norepinephrine to your entire system, even though you didn’t engage in strenuous physical activity all day.