Maybe you’re kissing a new partner or about to start a new job. Suddenly, your stomach is fluttering with fear. “Oh, they’re just butterflies,” someone might say. The phrase “butterflies in your stomach” doesn’t sound so bad, but in reality, those nervous pangs can often feel less like the gentle beating of a butterfly’s wings and more like a herd of elephants trampling across your intestines. Sometimes those so-called butterflies are also accompanied by nausea, making the situation thoroughly unpleasant. Why do our bodies react like this when we’re nervous?
According to The Conversation, we can thank our automatic nervous systems (ANS) whenever we get butterflies in our stomachs. There are two branches of the ANS: the sympathetic (colloquially referred to as “fight-or-flight”) and the parasympathetic (also called “rest-and-digest”). Both of them are constantly working in our bodies. The sympathetic system increases your heart rate, and your parasympathetic system decreases it.
Pretty simple so far, right? Your heartbeat is controlled by the balance of the two systems. When things are stable, your heart rate remains steady. After a big meal, your parasympathetic system redirects the flow of blood from your heart to your stomach, making you tired and more likely to relax and let your body digest your food. When you get nervous, though, your sympathetic system kicks into overdrive, elevating your heart rate. While this might not be comfortable, it actually provided an evolutionary advantage.
Imagine being confronted by a wild animal. Nerves hit you, and your fight-or-flight response kicks in. That sympathetic system overtakes your parasympathetic system, increasing your heart rate and flooding your body with adrenaline, giving you the energy to run away. In prehistoric times, this bodily reaction undoubtedly saved countless lives.
One of the effects of your sympathetic system taking over is the slowing down of digestion as blood is redirected away from your gut. The reduced oxygen and blood flow in your gut, and the reaction of the stomach’s sensory nerves to that, is what makes it feel like butterflies are in your stomach.
When our bodies perceive something as a threat, whether it’s a first date or giving a presentation, our sympathetic systems are likely to take over. It might not be comfortable or convenient, but it’s part of what helped homo sapiens get to the top of the food chain.
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