Chapter 3 - Meet your Amazing Brain

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Meet your amazing brain	119

a segment almost identical to that found in a lizard, a crocodile or a bird. Because of this, some scientists have dubbed it the "reptilian"8 brain. This part of the brain controls very simple but important functions: like our breathing, heart rate and many basic instincts. Turn a light on and any insect nearby will stop dead still. The bright light will send an instant signal to its tiny reptilian brain. Drive toward a bird sitting on the road and it will fly off an instant before you hit it; its reptilian brain has an in-built program to flee. Think of that next time you go to swat a fly - and it escapes a split second before the swat lands.
  Above your brain-stem is your second-tier brain. This limbic system is also often called the "old mammalian" brain - because it is similar to a major part of the brains of other mammals.
  Scientists say it started developing with the first warm-blooded mammals - or breast-feeding animals - between 200 and 300 million years ago. They say mammals still kept their "reptilian" brain, but added to it.
   It's the part of the brain that is programmed to instruct a baby - or a lamb or pup - instinctively to suckle its mother almost instantly after birth. And, as we'll find out later, it's significant that the emotional and sexual center of your brain is very closely connected with parts of the brain that deal with memory storage. You can remember things better when you are emotionally involved - like your first love affair.
  Sitting on top of the limbic system is the two-sided cerebrum and its cortex which caps everything else like a crumpled blanket. This cortex is only about 3 millimeters thick (about an eighth of an inch). But it has six layers, each with different functions. It is the part of our brain that makes humans a unique species. Depending on your beliefs, it is one of the phenomenal achievements of either creation or evolution, or both.

Neurons, dendrites, glial cells and insulating system
 
  Each of our 100 billion active neurons is a virtual computer in itself. Each is capable of sprouting between 2,000 and 20,000 branches, called dendrites - very much like the branches of a tree. Each of these stores information, and receives input from other cells.
  Each neuron in turn transmits its own messages around the brain, and around the body, along major pathways known as axons. Each axon in turn is covered with a "myelin" sheath. This is much like insulation around electric wires. The better the sheathing or insulation, the faster messages will speed along the "wires": up to 100 meters a second.

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