Your hunger and desire to eat goes back to early humans who had no assured supply of food. Back then, humans ate to build up a surplus (in the form of fat) in the event of famine.

Today we have more than a dozen neurotransmitters to nudge you towards eating (raising your weight) and a similar number of neurotransmitters to allay hunger (lowering your weight). A neurotransmitter is a chemical that helps transmit signals between the synapses (gaps between your neurons)that send messages to other neurons.

Your three-pound brain has about a hundred billion neurons and supporting glial cells. The neurons form many different groups, each focused on a different function of your body. Each neuron can receive signals from as many as two hundred thousand other neurons.

The electrical signals flow down the axons (long skinny part of neurons) at car interstate speeds. Most neurons communicate with other neurons in the brain. A small fraction of neurons send signals out to your spinal cord to cause your muscles to contract.

Returning to weight regulation, our neurons work together to keep us at a certain weight or “set point.”

When you eat less so your weight drops below your “set point,” your brain lowers your metabolic rate (energy needed to keep all your vital systems going).

This tendency will sabotage most diets. Then eating less results in no change to your weight. When you eat more, your brain tend to increase your metabolic rate to absorb some of those added calories.

   The hormone leptin is produced by fat cells. Leptin is released into the blood telling your body its fat level as well as indicating how the fat levels are changing. When there is less body fat, less leptin is released, telling your body to get more energy (in the form of food).

But when your body fat levels are high, more leptin is released and you don’t feel hungry.

Leptin receptors in your brain are in your hypothalamus, a brain region that regulates body temperature and sexual urges. Leptin also works in other parts of your brain, influencing your metabolism and regulates fat storage.

   Insulin is another hormone that is sensitive to stored body fat. Insulin is produced by the pancreas after meals. In the blood stream, insulin instructs cells to reduce the glucose going into the brain and to store energy.

Lean animals have lower levels of insulin than fat animals. Leptin level is a good measure of subcutaneous fat (fat near the skin) while insulin indicates the visceral fat that is distributed around your organs.

People with a lot of visceral fat are at greater risk for diabetes, high blood pressure and cardiovascular disease. Those of us with fat arms, fat thighs or calves (subcutaneous fat) have less risk than those of us with “beer bellies” (visceral fat). To have a “beer belly,” you don’t have to be a big beer drinker.

Other messengers can act to alter our appetites. Fatty acids and the hormone peptide YY seem to reduce eating while the hormone ghrelin, released around mealtime, increases hunger and food consumption.

For more information about weight regulation, read “Welcome To Your Brain,” a 2008 book by Sandra Aamodt and Sam Wang, both experts in neuroscience.

SKY SIGHTS AHEAD: The moon will be full on Friday, December 28 so there will be plenty of evening moonlight through the end of the year.

The nearly full moon will appear close to the planet Jupiter this Tuesday evening. Venus is a brilliant sight low in the 6:30 a.m. dawn.

Well above Venus at dawn is the planet Saturn. Saturn is then high enough for good telescopic viewing of its rings through modest telescopes with magnification of 30 and over.

Our 2013 Sky Sights features the sun’s positions along the zodiac, dates of the moon’s key phases (evening half full and full), when and where to spot the five bright planets and sunrise and sunset every 10 days for a number of Tri-State towns.

You can get a free copy of 2013 Sky Sights through the mail by leaving your name and mailing address on my voice mail at (301) 687-7799 or sending me an email with your name and mailing address. 2013 Sky Sights will also be posted on the FSU website early next year.

Bob Doyle invites any readers comments and questions. E-mail him at rdoyle@frostburg.edu . He is available as a speaker on his column topics.