10 Facts About the Amazing Brain Quiz

The most complex part of your body is your brain, which is responsible for your intelligence, your senses, how your body moves, and how you behave. At birth, the human brain weighs just 1 pound. By elementary school age, it's up to 2 pounds, and it finally weighs in at about 3 pounds as an adult. The adult human brain is about the size of a grapefruit, shaped like a walnut, and is a pinkish-gray color. About 80% of the brain is water, 10% fats, and the remaining 10% is protein, carbohydrates, soluble organics, and salt. It has a consistency of soft gelatin. Thirty-six ounces - the equivalent of three full soda cans - of blood flows through the brain.

When we sleep, our brain is very active, and dreams occur. The difference between being awake and being asleep depends on which brain systems are activated at a given time. Chemicals in the brain called neurotransmitters act on different nerve cells (neurons) in the brain, telling the brain to fall asleep as well as communicating which parts will remain active while we sleep.

Sleep is also critical for brain functions that we use when we are awake, such as memory, concentration, coordination, creativity, and well-being. A good night's sleep can strengthen all these areas. Without adequate sleep, people often have difficulty functioning.

It's a myth that we only use 10% of our brain. We actually use 100% of the brain, just not all at once. The brain only composes about 3% of our body's total weight, yet it consumes about 20% of our energy, so something is definitely going on up there! Even the smallest activity uses more than 10% of our brains – how much is used at any given time depends on what we are doing.

When brain chemicals malfunction it can lead to a host of problems, including mental illness, tremors, and symptoms related to Parkinson's disease, among other issues. In our brains, there are chemical and electrical processes that allow the brain to communicate with the nervous system. Neurotransmitters are nerve-signaling chemicals that send messages between neurons (groups of brain cells) that use electrical signals to pass along information. When the chemical processes of neurotransmitters malfunction, mental illness such as depression, anxiety, and other mood disorders can occur. When the electrical signals don't work properly, it can lead to tremors, seizures or Parkinson's disease symptoms, and other motor system disorders.

Your brain is divided down the middle and has two sides, or hemispheres. Each side controls the muscles on the opposite side of the body, thus the right side of the brain controls the movements on the left side of the body, and the left side of the brain controls muscles on the right side. If one side of the brain is damaged after stroke or traumatic brain injury (TBI), the opposite side of the body will be affected.

Your left brain hemisphere is also responsible for your development of skills in language, math, and logic, while the right hemisphere of the brain controls your spatial abilities, facial recognition, music, and visual imagery.

Creativity and wisdom do not automatically decline over time and wisdom often increases with age. It's true that the brain does shrink in volume and blood flow decreases as we age, but declines in thinking and memory are not inevitable. Each person is unique and some people will have cognitive declines, but many will have their abilities stay intact or even improve with age. The brain is capable of new learning throughout our lifetimes. Those who exercise regularly and who get a lot of intellectual stimulation are more likely to learn and retain new information and skills.

Short-term memory loss happens more frequently as we age, but it is not necessarily an early sign of Alzheimer's disease or dementia. As we get older, it is common to lose our car keys, or to forget someone's name. It can be disconcerting when it happens, but such lapses do not inevitably lead to severe mental declines. In fact, most older adults do not get Alzheimer's disease. Fewer than 1 in 5 people over age 65 will be diagnosed with the condition.

If you are experiencing memory loss that is of concern, talk to your doctor.

The brain consists of three main parts, the cerebrum, the cerebellum, and the brain stem, and each part has specific functions.
- Cerebrum: This fills most of the skull and is responsible for memory, problem solving, thinking, and emotions.
- Cerebellum: This part of the brain is located at the back of the head under the cerebrum and is responsible for balance and coordination.
- Brain stem: The stem is located under the cerebrum and in front of the cerebellum, and it connects the brain to the spinal cord. It controls functions such as breathing, digestion, heart rate, and blood pressure.

Dopamine is a neurotransmitter in the brain that is associated with pleasure. Dopamine also plays a role in body movement and functions such as motivation and attention. When dopamine activity decreases it can lead to movement disorders such as Parkinson's disease, as well as depression, anxiety, and schizophrenia. A number of medications used to treat mood disorders work by adjusting dopamine levels in the brain.

Another well-known neurotransmitter is serotonin, which helps us sleep, and also affects mood, behavior, appetite, pain perception, and body temperature regulation. Drugs that increase serotonin levels in the brain are often used to treat depression, eating disorders, and obsessive-compulsive disorders (OCD).

GABA (gamma-aminobutyric acid) is a neurotransmitter that helps control muscle activity. Epileptic seizures and Huntington's disease are often treated with drugs that increase GABA levels in the brain.

A neuron forest is a network of nerve cells and branches in the brain. Neurons are connected to each other by branches, and an adult brain contains about 100 billion neurons, with branches that connect at more than 100 trillion points and are the source for our thoughts, feelings, and memories. In a healthy brain these branches (dendrites) are smooth, but in a brain with Alzheimer's disease the neurons get tangled, and protein fragments (plaques) build up between the nerve cells, causing memory loss.