The human body has a mysterious way of sensing and displaying the ideas of a human mind. A sweet memory, a creaking sound at night, a scenic view, a thrilling experience or a piece of shocking news can cause your body to react making the hair on your skin surface stand.
The muscles that are attached to the hair on your skin surface gets contracted and create a shallow depression on the skin surface and this causes the skin surrounding that area to jut out a bit. These are called as Goosebumps. You get goosebumps even when you get cold or experience sudden chills.
We have Adrenaline glands with leaf-like structures sitting atop of our kidneys that secrete fear-and-fight hormones. These hormones are released when we feel strong emotions like fearing in dark, watching horror movies or expecting something fearful and also while fighting or protesting with intense emotional involvement. The release of these hormones signals to the brain, which sends an alert message to the muscles that are attached to the skin surface. Hence these muscles get contracted, which makes the outer skin protrude a bit resulting in Goosebumps. Getting goosebumps is a reflex phenomenon.
Adrenaline release can even cause sweaty palms and trembling hands at times. These are also the stress release hormones where people suddenly cry in times of feeling relief from stress. Increase in blood pressure and pulse rate or experiencing a feeling of having butterflies in the stomach are also the results of Adrenaline rush.
This phenomenon can also be seen in animals when they get threatened. When animals try to defend themselves from the attacker, they get goosebumps. The reflex phenomenon of producing goosebumps is called Piloerection or Pilomotor reflex. We know that porcupines raise their quills when threatened. From domestic animals to sea animals, most of them get goosebumps.