Final answer:
The brain consumes about half of the body's glucose, which is essential for its energy demands. Glucose consumption increases during cognitive tasks, but the brain can also utilize ketone bodies when glucose is limited.
Step-by-step explanation:
The brain consumes about half of the glucose circulating in the body. Glucose is the primary fuel for the brain, a carbohydrate that is essential for its function. The average adult brain might only represent 2% of our body's weight, but it uses a significant portion of the body's glucose - roughly 25%. Moreover, this consumption can increase in certain areas of the brain when tasks demand more cognitive effort, such as during difficult tests where intense concentration is necessary.
While most cells can use fatty acids as an alternative energy source, the brain relies heavily on glucose and, to a lesser extent, ketone bodies when glucose is scarce. Without sufficient glucose, brain function can deteriorate, potentially leading to unconsciousness. Despite sodium and potassium playing critical roles in cellular functions and the nervous system, they are not the primary fuels for the brain's energy demands.