If it's overactive, meaning it's too jumpy, it can signal a problem with an upper motor neuron, something in the spinal cord above the level of the knee jerk reflex, which is L3, L4, or something in the brain.
" Oh, dear" ! Pitty dropped her sewing in her lap and her mouth pressed up in hurt. " I declare, I don't know what ails you all tonight. You and India are just as jumpy and cross as two old sticks" .
He was oddly distracted and jumpy during lessons, losing the thread of what he was saying while talking to the class, answering questions wrongly, and all the time glancing anxiously at Umbridge all the time.
This is the hygiene hypothesis, it says growing up around a less diverse bunch of microbes can make our immune systems kinda jumpy and nervous later in life.
The surprise is that, as traders rushed to price in Mr Trump's sweeping victory, the collective judgment reached in the biggest markets of all was: " a lot less jumpy than before" .