Your nervous system is full of survival triggered responses designed to keep you alive and healthy.
When falling asleep you may remember getting a slight jerk sensation in either your fingers or feet. This is called a myoclonic jerk. This event can be caused by the common sensation of low oxygen in the brain. The brain then attempts to correct your breathing by startling you awake.
Myoclonic jerks are common as you begin to fall asleep because your breathing will slow down faster than your heart rate. This can lead to temporary lower oxygen saturation in the brain, which can trigger a survival response called a myoclonic jerk.
National institute of neurological disorders
Pruning skin in water
If you’ve ever taken a bath or spent time in the pool you have probably noticed an interesting phenomenon that occurs right on your fingertips. Pruning of the fingertips often has a white-ish color. This is your body’s way of compensating for a wet environment by creating an effective way to grip onto slippery surfaces. The mechanism for this is poorly understood and more research is underway.
Water-induced finger wrinkles improve handling of wet objects by: Kyriacos Kareklas
If you ever watched a scary movie or felt a cool breeze after getting out of a swimming pool, you have probably felt the sensation known as goosebumps. These tiny temporary bumps on your skin are your body’s way of adapting to a changing environment. Goosebumps can either be caused by a change in temperature or sense of excitement or danger.
The reaction to cold temperature makes the hairs on your skin stand up and create a layer of insulation and protection from the cold. This was more helpful to our ancestors who didn’t have the modern conveniences of coats and furnaces.
A reaction to excitement or danger is also very common; physiologically your body is unable to differentiate between excitement or fear. Your body will respond roughly the same whether you are walking down the aisle at your wedding or being chased by a bear. The release of adrenaline will create the same response of increased energy and goosebumps. When our ancestors had to defend themselves it was a benefit to make yourself appear larger than you really were as a means of intimidation. Goosebumps were more effective for this purpose then, when our ancestors had more body hair.
George A.Bubenik: Physiologist and Professor of Zoology at the University of Guelph