Although it accounts for only about 2 percent of body weight, the human brain consumes roughly 20 percent of the body’s energy and contains around 86 billion neurons, a combination of high metabolic demand and immense cellular complexity that underpins cognition, sensation and behaviour.
Metabolic demand
The brain’s disproportionate energy use reflects constant activity required to maintain resting membrane potentials, support synaptic transmission and fuel astrocyte‑neuron metabolic coupling; even during quiet wakefulness the organ burns a substantial fraction of the body’s glucose and oxygen supply.
Neurons and connections
Roughly 86 billion neurons form dense networks with trillions of synapses, and it is the patterns of these connections and their dynamic signalling that enable perception, memory, language and abstract thought rather than mere cell counts alone.
Efficiency and plasticity
The brain balances remarkable energy efficiency with flexibility: synaptic plasticity, neurogenesis in specific regions and large‑scale network reorganisation let it adapt to new experiences, learn throughout life and recover to varying degrees after injury.
Clinical and lifespan notes
Because the brain depends on continuous blood flow and metabolic support, disruptions such as hypoxia, stroke or chronic metabolic disease have outsized effects on function; protecting cerebral health through cardiovascular fitness, sleep, nutrition and management of vascular risk factors helps preserve cognitive capacity across the lifespan.
Quick related facts
- Relative mass: ~2% of total body weight.
- Energy use: ~20% of resting metabolic energy.
- Neuron count: ~86 billion neurons.
- Key features: high metabolic demand; dense connectivity; lifelong plasticity.