The Brain: The Command Center of The Body.
The brain is active all the time, not only in wakefulness but also in sleep. Therefore, it, like the heart, is critically in need of a continuous supply of metabolic fuel substances (energy) and oxygen provided by the blood flow. Exercise is one of the best ways to stimulate blood and oxygen flow to the brain to keep it nourished and healthy.
I will be dividing this topic into three divisions; BRAIN DEPENDENCY ON GLUCOSE AND OXYGEN, BRAIN BLOOD FLOW, BRAIN FLOW AND LOCALIZATION.
Brain Dependency on Glucose and Oxygen
In contrast to other active body organs (e.g., heart, muscle) which utilize alternative fuels like the fatty acids, the brain under normal conditions, depends almost exclusively on glucose to obtain its energy needs. Marked hypoglycemia (e.g., due to a large insulin dose) may lead to fainting, convulsions, coma, or death. Interestingly, after days of starvation, the brain develops the capacity (enzymes) to use ketone bodies (a product of fatty acid metabolism in the liver, as an alternative energy source. This capacity is present in the newborn brain but disappears after infancy. The brain’s critical dependency on glucose is one of the bases for the existence of many regulatory mechanisms for blood glucose homeostasis.
To produce the large quantity of ATP required by brain cells, the Kreb’s cycle/oxidative phosphorylation pathway is utilized. This acccounts for the brain’s high and critical dependence of oxygen. In adults, 10 seconds of anoxia (oxygen deprivation) is sufficient to lose consciousness and higher brain functions (fainting). A few minutes of hypoxia can lead to coma and severe and irreversible brain damage, death can occur due to the loss of function in the vital respiratory centers of the medula.
In adults, brain weight is about 1.4 (3lbs) and the brain has an oxygen consumption rate of about 50 cc per min. Thus, although the brain’s weight is only 2% of the body’s, its oxygen consumption rate (metabolic rate) is about 20% of the whole body’s. Why does the brain require such a highe metabolic rate? Its work depends heavily on formation, propagation, synaptic transmission, and integration of a variety of electrochemical potentials, cellular functions requiring the maintenance of proper ionic gradients. To do this, the brain cell membranes contain one of the largest concentrations of sodium-potassium pumps in the body. These pumps are ATP dependent, they involve the operation of the plasma membrane enzyme Na-K-ATPase, which is also present in the brain in large concentrations. The sodium pump uses most of the ATP produced in the brain.
In neurons, the synapses on dendrites and cell bodies use the greatest amount of energy. Therefore, the synapse-rich areas (e.g., the gray matter (cortex, basal ganglia, and subcortical nuclei) have generally high metabolic rates, and synaspe-poor areas (e.g., the fatty white matter (mylenlinated nerve fibers) have low rates. Among the gray matter areas, relative rates vary. The forebrain basal ganglia and the mid brain inferior colliculi show very high rates; the cortex of the cerebrum and cerebellum have moderately high rates; the thalamus and the nuclei of the cerebellum and medulla show medium rate; the lowest rates are associated with spinal cord white matter.
Exercise and proper nutrition is crucial for healthy brain activity. In part two I will be discussing Brain Blood Flow.
Daryl Conant, M.Ed.