Adult neurons rely heavily on which of the following?
(a) Glucose
(b) Protein
(c) Potassium
(d) Sodium 

Choose the correct answer from the options given below:

Correct option is A

The correct answer is A only – Glucose.

1. Adult neurons depend almost exclusively on glucose as their primary source of energy under normal physiological conditions.
2. Unlike other cells, neurons are highly metabolically active and require a constant supply of glucose to maintain membrane potentials, produce neurotransmitters, and support synaptic activity.
3. Glucose is metabolized through glycolysis and the citric acid cycle, leading to the generation of ATP, which is essential for various neuronal functions.
4. In the absence of glucose, neuronal function deteriorates rapidly, and prolonged deprivation can result in irreversible damage or cell death, highlighting the critical role of glucose in brain metabolism.
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Information Booster

1. Glucose as Brain Fuel:
1.1 The brain consumes about 20–25% of the body’s glucose despite representing only about 2% of total body weight.
1.2 Neurons do not store glucose and depend on a continuous blood supply to deliver glucose from the bloodstream.
1.3 Hypoglycemia (low blood sugar) can lead to confusion, seizures, and unconsciousness due to impaired neuronal activity.

2. Glucose Transport:
2.1 Glucose enters neurons via specialized transport proteins called GLUTs (Glucose Transporters)—mainly GLUT3 in neurons and GLUT1 in the blood-brain barrier.
2.2 These transporters help maintain the high metabolic demand of brain cells even during fluctuating glucose levels.

3. Role in ATP Production:
3.1 Glucose undergoes aerobic metabolism in mitochondria to produce ATP, which powers essential functions like ion pumping, neurotransmitter release, and signal transduction.

4. Alternative Fuels (Only in Special Conditions):
4.1 In starvation or prolonged fasting, neurons can adapt to use ketone bodies as an alternative fuel, but this is not their preferred or primary energy source under normal conditions.
4.2 This adaptation is temporary and cannot fully replace the functions supported by glucose metabolism.

Additional Information

Protein (Option B):
1.1 While proteins are essential for structural and enzymatic functions in neurons, they are not used as a primary energy source.
1.2 Protein catabolism for energy is inefficient and occurs only under extreme conditions like malnutrition or prolonged fasting.

Potassium (Option C):
2.1 Potassium ions play a critical role in maintaining the resting membrane potential and in generating action potentials, but they do not serve as an energy source.
2.2 Potassium’s role is in electrophysiological signaling, not energy metabolism.

Sodium (Option D):
3.1 Sodium ions are vital for action potentials and neurotransmission, but like potassium, they are not an energy source.
3.2 The sodium-potassium pump (Na⁺/K⁺-ATPase) uses ATP (produced from glucose) to maintain ion gradients.