Insulin tells cells throughout the body about the level of glucose available

This signal sent by the beta cells, in the form of insulin, is received by specific cells throughout the body.  The receptor cells all have specific proteins called insulin receptors.  When, insulin binds to insulin receptors, the receptor cells alter their behavior.  One example of a receptor cell is in the liver.  When insulin is released by the pancreas, parts of the liver increase the production of glycogen.  Glycogen is made from glucose. It can be stored in the liver and later released in the form of glucose, when blood glucose levels too low.  Many other cells have insulin receptors, indicating they are regulated by insulin.  These include fat cells, which increase the production of triglycerides in response to the presence of insulin.

Cells in the brain are particularly dependent upon glucose.  Most other cells in the body can use other forms of molecular fuel, like fatty acids.  The brain, however, depends on glucose to function.  The liver stores glucose in the form of glycogen, when bloodstream glucose levels are high and releases glucose when bloodstream levels are low.  The liver, then, keeps the brain fed between meals.

Very low blood sugar for a sustained period of time depletes the liver’s storage of glucose.  This condition can be caused by excess insulin in the blood stream.  The condition starves the brain of fuel, leading to various problems with the central nervous system including, confusion, delirium, dizziness, and eventually partial loss of brain function, a coma.  This state is known as hypoglycemia, it can be caused by an overdose of insulin.  Despite the serious symptoms, hypoglycemia is easily cured.  One just needs to raise the glucose levels of the blood, usually by eating candy, a small amount of sugar or drinking a small amount of fruit juice, soda (non-diet), or milk.