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The Amazing Human Brain
- Weighs 2.5 lbs. and is composed of 75% water.
- Occupies 85 cubic inches (about the space taken by 3 pints of milk).
- Contains 100 billion neurons, forming estimated 500 trillion synapses (connections).
- Brain neurons are electrically excitable cells that process and transmit information.
- A neuron can be directly linked to tens of thousands of other neurons, creating more than a hundred trillion connections – each capable of performing 200 calculations per second!
- The simplest dichotomy related to the processing of threats is the fight-or-flight response mediated by the amygdala and hypothalamus in the mid-brain region.
- The brain consumes 75% of the blood sugar created by the liver.
- Each minute, over 1.5 pints of blood flows over the brain.
- Being only 1/15th of the body’s weight, the brain receives 20% of its blood.
- The brain also consumes 20% of the oxygen a human breathes.
- Just 10 seconds without blood and oxygen brings unconsciousness.
- Six minutes without oxygen brings irreversible death of brain cells.
Brainstem: controls the reflexes and automatic functions (heart rate, blood pressure), limb movements and visceral functions (digestion, urination).
Cerebellum – comprises about 11% of the brain‘s weight. Receives sensory information from the muscles, joints and tendons to adjust posture and coordinate muscular movements ordered by the cerebrum.
Limbic System – a wishbone-shaped structure that encircles the brainstem and functions as a mini brain to handling emotions and memory. The structures of the limbic system arouse or temper feelings ranging from joy and love to hate and emotional suffering.
a. Thalamus – input-output relay station that sends incoming sensory information to areas of the cerebral cortex (all brain waves travel between the thalamus and the cortex); determines which sensory information reaches consciousness and sends out motor-information from the cerebellum, out to the body’s muscles
b. Hypothalamus - contains nuclei that control hormonal secretions from the pituitary gland. These centers govern, sexual reproduction, eating, drinking and growth. The hypothalamus is the essential coordinator of the central nervous system and is also involved in almost all crucial aspects of behavior (sex drive, water balance, heat control, hunger, aggression, pleasure), including your biological "clock," which is linked to the daily light-dark cycle (circadian rhythms). The hypothalamus initiates the fight-or-flight response in the body.
c. Amygdala – almond-shaped group of neurons that play a primary role in processing and memory of emotional reactions – aggression, anger, fear, excitement and sexual drive. The amygdala sends impulses to the hypothalamus for activation of the sympathetic nervous system (the fight-or-flight response).
Hippocampus – plays an important role in new memories about experienced events, factual memories and spatial navigation. In Alzheimer's disease, the hippocampus becomes one of the first regions of the brain to suffer damage; memory problems and disorientation appear among the first symptoms.
Midbrain - The midbrain contains nuclei that link the various sections of the brain involved in motor functions (cerebellum, basal ganglia, cerebral cortex), eye movements and auditory control.
Cerebrum (also called the cerebral cortex): consists of the cortex, large fiber tracts (corpus callosum) and deeper structures (basal ganglia, amygdala, hippocampus). 85% of the human brain is comprised of the cerebral cortex. It is the seat of our intelligence, integrating information from all of the sense organs, initiates motor functions, controls emotions.
Left hemisphere of Cerebrum: controls logical, analytical thinking, verbal, mathematical and task-solving abilities. Right hemisphere: controls how we see the world, viso-spatial skills – seeing color, shape, space-perception, music (perceives the whole picture, conceives overall meaning).
Grey Matter: The surface of the cerebrum is composed of grey matter (about 1/4-inch in thickness), which functions to process information. This fragile sheath contains around 8000 million nerve cells (neurons), which are interlinked by 10,00o miles of fibers. The grey matter functions in processing data (thinking and reasoning).
White Matter: Beneath the grey matter, lies the white matter comprised of hundreds of millions of nerve fibers (axons) that connect neurons, uniting different regions of the cerebrum. The white matter receives its color from the fatty insulating sheath call myelin, which protectively surrounds the axons. Traditional medical data has always specified that the white matter of the brain functions only for transmitting data that was processed by the grey matter. However, new research described below sheds new light on white matter’s role.
New Discoveries About the Brain’s White Matter
Scientists at Johns Hopkins University have found that nerves in the brain’s white matter have a more complex role that just conveying information between different regions of the brain.
Using mouse cells for their study, published in the March issue of Nature Neuroscience, their research reveals that brain cells communicate with each other in more dynamic ways than was ever known before. Lead by Dwight Bergles, Ph.D., an associate professor of neuroscience at Hopkins, the researchers were able to observe nerve axons “talking” to other cells in the white matter.
Their discovery centers on certain precursor cells called OPCs. When these cells grow into mature versions (called oligodendrocytes) they wrap themselves around nerves, insulating them with a whitish coat of protective myelin (thus fulfilling the white matter characteristic).
To study the OPCs, researchers chose to monitor individual precursor cells in the corpus callosum, a white matter section that connects the two brain hemispheres. The surprising results showed that the OPCs were discovered to have a similar activity found in the grey matter – that of using the neurotransmitter glutamate to produce electrical signals.
To further investigate, the research team forced single nerve cells to become excited individually and observed that as the electrical signals were carried along the nerves, glutamate was released, causing electrical signals to be produced.
All white matter nerve cells releasing glutamate within the OPCs had no myelin insulation – a process previously thought to only occur in the grey matter of the brain.
Dr. Bergles’s team now theorize that the white matter activity his team has observed may help uncoated nerve cells near the precursor cells to signal for (and thus receive), a myelin coating, in order to replace another cell that was damaged. A myelin coating acts to speed electrical impulses, causing the cells to fire 20 to 90 times faster. Myelin loss is documented to degrade signal communication in nerves, as in neurodegenerative diseases such as multiple sclerosis.
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Sources: Neuroscience of Mental Health - Complexities of the Brain- Parts I, II, III (ww.surgeongeneral.gov) Wikipedia (http://en.wikipedia.org) Medline Dictionary (http://en.wikipedia.org) Health Information - National Institutes of Health (http://health.nih.gov)
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