Brain cells and neurons are not the same thing. Neurons are one type of brain cell, but they share the brain with a roughly equal number of non-neuronal cells called glial cells. The human brain contains about 86 billion neurons and 85 billion glial cells. So when people say “brain cells,” they’re referring to a broader category that includes neurons and several other cell types, each with distinct jobs.
What Neurons Actually Do
Neurons are the brain cells responsible for generating and transmitting electrical and chemical signals. They’re the cells people usually picture when they think of brain activity: processing information, forming memories, controlling movement, interpreting what you see and hear. A neuron carries information within itself as an electrical impulse. When that impulse reaches the end of the neuron, it gets converted into a chemical message. Small molecules called neurotransmitters cross a tiny gap between neurons, land on the receiving neuron, and either encourage or discourage it from firing its own electrical signal.
Structurally, neurons have a distinctive shape. Branch-like extensions called dendrites receive incoming signals from other neurons. A long, tube-like projection called an axon carries the signal away from the cell body toward the next neuron. This basic architecture, dendrites in and axon out, is what allows chains of neurons to relay information across the brain in milliseconds.
The Other Half: Glial Cells
For decades, textbooks claimed glial cells outnumbered neurons 10 to 1. That figure turned out to be wrong. More careful counting methods, validated in 2009, show the ratio across the whole human brain is closer to 1 to 1. The old “10 to 1” number persisted for half a century before anyone directly counted, which says something about how overlooked these cells were.
Glia were long treated as passive scaffolding, but they actively shape how the brain functions. There are several types, each with a specialized role.
Astrocytes
Astrocytes are irregularly shaped cells with long, sprawling extensions. They maintain the chemical environment neurons need to work properly, regulating water and ion levels around synapses. They also help maintain the blood-brain barrier, the selective filter that controls what gets from your bloodstream into brain tissue. When the brain is injured or diseased, astrocytes help contain the damage by blocking inflammation and protecting surrounding healthy tissue.
Oligodendrocytes
Oligodendrocytes wrap layers of a fatty substance called myelin around neuron axons, creating an insulating sheath. This insulation allows electrical signals to jump rapidly along the axon rather than traveling inch by inch. The result: myelinated nerve fibers transmit signals up to 50 times faster than unmyelinated ones. A single oligodendrocyte can insulate portions of up to 50 different axons simultaneously. When these cells die or malfunction, the myelin breaks down, slowing or disrupting signal transmission. This is exactly what happens in conditions like multiple sclerosis.
Microglia
Microglia are the brain’s immune cells. In their normal “resting” state, they monitor the local environment, help prune unnecessary connections between neurons during development, and fine-tune how synapses work. When something goes wrong (infection, injury, or neurodegenerative disease), microglia shift into an activated state. They multiply, migrate toward the problem, and engulf damaged cells and debris. Dying cells release chemical “find me” signals that recruit microglia, followed by “eat me” signals that trigger the cleanup process. Microglia also play a more surprising role: they can actively induce certain neurons to die, which is a normal and necessary part of brain development that helps sculpt healthy neural circuits.
Why the Confusion Exists
In everyday language, “brain cells” and “neurons” get used interchangeably because neurons are the most famous brain cell. They’re the ones doing the signaling that underlies thought, sensation, and movement. When someone jokes about “killing brain cells,” they almost always mean neurons. Pop science coverage reinforces this by focusing on neurons and rarely mentioning glia.
The conflation also has roots in scientific history. For most of the 20th century, researchers treated glial cells as little more than structural glue (the word “glia” comes from the Greek for glue). It’s only in recent decades that science has recognized glia as active participants in brain function, involved in everything from immune defense to the speed of your thoughts.
How Neurons and Glia Work Together
Neurons can’t function without glial support. Astrocytes regulate the chemical soup that neurons sit in, ensuring conditions stay stable enough for reliable signaling. Oligodendrocytes dramatically accelerate the speed at which neurons communicate. Microglia clear out dead or damaged neurons and help shape which synaptic connections survive during brain development. Glia also modulate neuron signaling directly, influencing how strong or weak a connection between two neurons becomes.
Think of it this way: neurons are the players on the field, but glial cells are the coaching staff, medical team, and grounds crew combined. The game doesn’t happen without either group. When glial cells malfunction, the consequences are severe. Oligodendrocyte loss leads to demyelination and conditions like MS. Overactive microglia are implicated in neurodegenerative diseases. Astrocyte dysfunction disrupts the blood-brain barrier and leaves neurons vulnerable to toxins.
The Numbers at a Glance
- Total neurons: approximately 86 billion, with the vast majority (around 101 billion by some estimates) packed into the cerebellum, the region handling coordination and balance
- Total glial cells: approximately 85 billion
- Glia-to-neuron ratio: roughly 1 to 1 across the whole brain, though specific regions vary
The cerebral cortex, the wrinkled outer layer associated with higher thinking, holds an estimated 21 to 26 billion neurons. The cerebellum, despite being much smaller in size, contains far more neurons, though they’re tiny and densely packed. Different brain regions also have different glia-to-neuron ratios, so the 1 to 1 figure is a whole-brain average rather than a universal rule.