Neurons might get all the credit, but behind the scenes, glial cells are doing just as much to keep your nervous system working. They don’t get much attention, but without them, neurons wouldn’t stand a chance.

Myelination

Let’s start with myelination. That’s the process of wrapping axons in a fatty layer, kind of like insulating a wire. It speeds up electrical signals so they don’t leak out or slow down. In the peripheral nervous system, this job belongs to Schwann cells. Each one wraps around a single segment of a single axon to create a neat little coil. But in the central nervous system (the brain and spinal cord) it’s a different cell type entirely. Oligodendrocytes do the myelinating there, and unlike Schwann cells, they multitask. A single oligodendrocyte can stretch out to wrap multiple axons at once.

Other Glial Cells

But glia do more than just wrap wires. Astrocytes, for example, are star-shaped cells that help maintain the blood-brain barrier. This barrier decides what can and can’t enter the brain from the blood, so it lets in things like glucose and oxygen, while keeping out harmful substances.

Then there are ependymal cells, which line the fluid-filled spaces of the brain and spinal cord. They help make and circulate cerebrospinal fluid, which cushions the brain and keeps it clean.

Microglia act as the immune system of the brain. They’re constantly looking for anything that doesn’t belong, such as dead cells, debris, or pathogens, and they clean it up before it causes trouble.

Neuroplasticity

As the nervous system matures, it stays flexible, thanks to something called neuroplasticity. That’s the brain’s ability to rewire itself, which becomes especially important in learning, memory, and recovery from injury. The wiring itself (synapses between neurons) can change over time. Some get stronger, a process known as long-term potentiation, and others get weaker, known as long-term depression. You’ll see both happening when someone’s learning a new language, learning to ride a bike, recovering from a stroke, or just forming memories of everyday life.

How the Nervous System Forms

Now let’s back up. Where does the nervous system even come from? During early development, a structure called the notochord sends chemical signals to a sheet of cells known as the ectoderm. These signals cause the ectoderm to fold in on itself to form the neural tube, which eventually becomes the brain and spinal cord.

Along the edges of this folding process, a special group of cells called neural crest cells peel off and migrate to other parts of the body. These cells are incredibly flexible in what they become. Depending on where they travel and what signals they pick up, they might turn into pigment cells in the skin, bone and cartilage in the face, parts of the peripheral nervous system, or even the adrenal medulla, which pumps out stress hormones. One especially fascinating outcome is the enteric nervous system, the “second brain” in your gut, which also arises from these wandering cells. It’s a dense network of neurons that helps control digestion to move food along and regulate enzymes without needing input from the brain. In fact, it uses many of the same neurotransmitters found in the brain and is involved in things like appetite, mood, and even stress responses.