90% of the brain are not neurons. What does it mean for the long-term brain health?

90% of the brain is not made up of neurons. This holds a profound significance of non-neural cells for the long-term health of our brain.

There’s a bustling community of cells beyond just the famous neurons in the human adult brain. While the brain houses approximately 86 billion neurons (1), these aren’t the sole inhabitants. Although neurons are the cells that should not be overlooked as they are responsible for communication, “computation,” and memory storage, the pillars of the brain are the glial cells.

Glial cells, in contrast to neurons, come in various sizes and serve a multitude of functions. While neurons are known for their size and their role in transmitting electrical signals, glial cells, being smaller, play diverse support roles that are crucial for maintaining the brain’s health. The most important ones among these nonneuronal cells are astrocytes, oligodendrocytes, and microglia. These hard-to-pronounce names hide a world of complexity and intrigue, each with its unique contribution to brain health.

Astrocytes are the most abundant cells in the brain and occupy roughly 50% of the brain volume (6,7). The cell looks like a star, and when it comes to brain health, it truly is a star. An astrocyte is like a “renaissance man.” It’s a multitasker that regulates chemical composition, participates in signaling processes, serves as an additional energy storage, and provides nutrients to neurons. Astrocytes manage the growth of new neurons and synaptic connections (7). They regulate blood flow in the brain and keep the brain safe by maintaining the brain’s barrier (BBB). And if damage in the brain occurs, who will repair it? Astrocytes, of course. Focus on keeping astrocytes in shape, and you’ve almost won the battle for long-term brain health.

Oligodendrocytes comprise roughly 5–10% of brain cells (8). These cells provide insulation to neurons by forming myelin sheaths around their axons, enabling efficient transmission of electrical impulses, crucial for speedy communication between brain regions (9). Furthermore, they assure axonal integrity and metabolic support to neurons (10).

Last but not least, microglia, the brain’s immune cells, account for about 10–15% of brain cells (11). They act as vigilant sentinels, patrolling the brain to clear out debris and defend against pathogens, ensuring a clean and safe environment (12).

Contrary to the popular belief that our brains are fixed structures, there’s a continuous process of neurogenesis and cell turnover. While neurons are mainly formed before birth, glial cells, particularly astrocytes, continue to mature into adulthood, influencing brain function throughout life (13). New neurons and glial cells are constantly being born, while old ones are dying. This dynamic process, which continues throughout our lives, contributes to brain plasticity, allowing us to learn and adapt to the world around us. The brain's ever-changing nature is truly fascinating.

Each brain cell type possesses varying iron levels and other metals, impacting their susceptibility to ferroptosis, a cell death mechanism triggered by iron accumulation (14). This phenomenon exemplifies the diverse vulnerability and resilience among brain cells. Understanding these distinctions sheds light on the mechanisms underlying various age-related brain diseases and the importance of tailored treatments targeting specific cell types (15).

Despite their differences, neurons and glial cells collaborate synergistically, forming intricate networks crucial for optimal brain function. Each cell type relies on the others, showcasing the brain’s remarkable interconnectedness. The brain is a bustling ecosystem where neurons and glial cells coexist harmoniously, each playing a vital role in maintaining brain health and function. Without any of these cell types, the balance in our brain would be disrupted, highlighting that every neuron and glial cell in our brain is necessary to maintain a healthy and functioning brain.

References

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