Surprise!_Michael_Cunningham_by_David_Shankbone
Because of the great rush of adrenaline in the body. Whenever there is a stress or emergency situation, this substance is released by the adrenal gland, located – as the name says – above the kidneys. When this discharge occurs, receptors present in human body tissues – called adrenergic receptors – send a large number of signals to the brain, preparing the organism to face the threatening situation. Because this adrenergic rush often occurs in dangerous situations, the brain stimulates the peripheral nervous system, sending signals to help the body react. In the case of a fright, the possible reactions are flight or confrontation – through a fight, for example. The pupils dilate, for the person to see better, the heart rate accelerates and the blood pressure increases – thus, the muscles receive more oxygen and greater blood irrigation for an intense and fast physical activity.
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“Normally we have slight tremors caused by semi-contractions in the muscles, which give us balance”, says neurologist Luiz A. de Andrade, from Escola Paulista de Medicina. “But the increased flow of information to the brain interferes with this balance, causing exaggerated tremors.”