How to Tell Crystal From Glass. Here are some quick tips on how to distinguish classic crystal from plain glass. 1  Hold up a glass to the light. 2  If the glass acts as a prism and you see a rainbow you are holding crystal. 3  If not, it is just plain glass. 4  When struck, crystal produces a musical ring.
Blood pressure is controlled by tiny muscles that line the inside of your blood vessels. These muscles allow your arteries to operate like soft rubber tubes, that expand with each beat of your heart. When these muscles throughout the vascular system [the arteries and veins that carry blood] expand, blood pressure drops.
NEXT PAGENEXT. To control your blood pressure, your body must adjust how much blood is pumped through your heart. Your body must also adjust the amount of pressure in your blood vessels. How Your Brain Responds. When your blood pressure begins to fall too low, a signal is sent to your brain. Your brain responds by producing chemicals called neurotransmitters.