The human brain consists of more than 100 billion brain cells and weighs about 3 pounds by adulthood. The organization and size of the brain reflect its function. For example, the largest part of the brain is the cerebral cortex, responsible for conscious thought. It takes up 77 percent of the volume of a human brain, but only 31 percent of a rat's brain, according to Washington University.
Brain Messages
Your brain sends impulses from the neurons to the rest of the nervous system, along the spinal cord. Your brain is responsible for your sensations and activities. Damage to any part of the brain leads to mental or physical changes in the body, and is likely to be permanent. The ganglia that carry brain messages cross over as they leave the brain through the skull, at the back of the head. This means that damage to the left side of your brain affects the right side of your body. Your bony skull protects your brain, and tough membranes, called meninges, surround the cortex.
Life Support
The brain stem and limbic system, situated deep within the cortex, maintain the body's essential functions, controlling heart rate, blood pressure and breathing. The hypothalamus maintains your body temperature and enables you to recognize hunger and thirst. It allows you to learn and remember, control your emotions and coordinate your movements.
Thought
The cortex, gray and folded in appearance, allows thought, language, perception, voluntary movement and reasoning. There are two halves: a left and a right hemisphere. The corpus callosum, a strong band of nerve fibers, connects the two sides, allowing integrated thought using both sides of the brain. Frontal lobes are responsible for temperament and behavior. Temporal lobes lie on either side of the head and allow language use. Parietal lobes govern motor activity, and occipital lobes manage visual impulses. The cerebellum, situated behind the brain stem, consists of two hemispheres and manages posture and balance.
Brain Chemistry
Your brain needs chemicals to activate it. Dopamine triggers nerve activity, according to the Royal Society of Chemists, before nerve cells absorb it. Some mood-enhancing drugs cause the release of more dopamine, while others prevent its absorption. Chemical substances in the brain are associated with schizophrenia and other mental health conditions, as well as with drug and sugar addictions.
Aging
The PBS.org website suggests that normal aging of the brain does not necessarily lead to the loss of large numbers of neurons. In fact, new neurons are produced into old age. Although the speed of mental functions may slow, and people over 70 may forget names or phone numbers, brain functions that rely on learned information and vocabulary can improve with aging. Some neurons appear to adapt and change, growing new branches and links, countering the effects of atrophy of other nearby neurons.
