After a nerve-racking day, a nervy man may well get on our nerves. Nervous about offending him, we nevertheless work up the nerve to tell him he has some nerve to so freely enervate us. After arguing for an hour, our nerves are shot.
The English language is replete with terms and expressions that relate strong negative emotions to nerves. The connection is so strong that (in my experience) many English speakers tend to associate symptoms of negative emotions, such as clenched teeth, clenched fists, trembling, shortness of breath, etc. with literal nerves.
To be sure, nerves relay signals between our brains and muscles, and therefore play a role in the physiological response to negative emotions. However, as I see it, there's nothing particularly special or meaningful about the connection between the two.
For one thing, nerves play no role in the genesis of emotions (yes, the brain is technically part of the nervous system, but I highly doubt this antomical factoid explains the origin of the expressions).
For another, nerves play no more distinct a role in the response to negative emotions than many other physiological features: hormones, lungs, veins, muscles, the face, the eyes, etc. Notwithstanding the observation that shaking and numbness are two symptoms of extreme exertion, upset, or distress, and that nerves play a role in both, I see nothing to suggest why literal nerves and metaphorical nerve, nerves, and nervousness ought to be related. Why not use the face, heart, skin, or eyes consistently as a metaphor?
And if we associate nerves with negative emotions, why not also with positive emotions? Why does "getting on my nerves" not describe the physical feeling of euphoria in young love, and "I'm so unnerved" not describe ASMR (i.e. the warm fuzzies), which is a phenomenon directly and near-exclusively associated with the nervous system?
How many English speakers of old were even aware of what nerves are and what their anatomical role in the body is? Would a layperson have known, for instance, that nerves were the organ responsible for conveying sensations of pain, skin irritation, etc. at the time the terms/idioms came into use?
My question: Where does the link between physical nerves and expressions pertaining to anxiety, irritation, agitation, and audacity originate? What was the reasoning behind it? Is it unique to English, universal to all languages, or somewhere in between?
(Note that I'm omitting expressions such as "strike a nerve", "drilling into a nerve", etc., since the connection to literal nerves is obvious in these cases.)