Glial cells: more than neurons little helpers
By: Malte Borggrewe
Tags: Brain, Biology, Science, Science Communication, Neuroscience

The functional elements of the brain are nerve cells, called neurons. They represent a network of interconnected cells which communicate via electrical impulses. Neurons are the reason we can move, taste, see, memorise, and learn. These specialised cells, however, require a lot of support to fulfil their function. This support is given by surrounding cells: the glia cells.

Glia cells got their name from observations in the 19th century, where they were described as “nerve glue” without a particular function. Nowadays we know better: glia cells are absolutely crucial for proper brain function. Glia cell dysfunction can lead and contribute to severe conditions such as neurodegenerative diseases (Alzheimer’s, Parkinsons, and more), stroke, multiple sclerosis, and many more.

But what is the role of glia cells in this intricate network of neurons? Why exactly are they so important? Let’s find out by looking at the function of these glia cells. There are multiple types of glia cells and we will focus on the 3 main types: oligodendrocytes, astrocytes, and microglia.

Oligodendrocytes: the insulators

A neuron is a bit like a battery: it can give an electric impulse which is transmitted to other neurons or eventually muscles, for example, so they can contract. If we connect batteries with a lightbulb, we do that using insulated cables. The equivalent of a cable would be an axon, which are a bit like the long arms of neurons. These axons are insulated as well, in order to allow fast travel of electrical impulses, and so these impulses do not jump to neighbouring axons. Neurons cannot insulate their axons. This task is done by oligodendrocytes. Oligodendrocytes generate lipid sheaths (called myelin), which are wrapped around axons and serve as an insulation. During a disease called multiple sclerosis, oligodendrocytes die and these sheaths are destroyed. This can lead to loss of vision, paralysis, and death.

Astrocytes: jack-of-all-trades

Astrocytes are the most abundant cell type of the brain and get their name from their star-like appearance. One astrocyte can have contact with up to 2,000,000 neurons. That’s just astonishing if you ask me. Astrocytes have a variety of functions. For one, they provide neurons and oligodendrocytes with food. Some important compounds cannot be produced by neurons themselves, so they rely on astrocytes to feed these resources. Astrocytes can take up and release neurotransmitters as well, which helps neurons with their electrical transmission. Furthermore, astrocytes help to regulate the blood flow in the brain, and they are involved in selecting which compounds can enter the brain and which ones should not. As you can see, these are very versatile cells.

Microglia: the immune cells

Microglia, as their name suggests, are small glia cells. They are the main immune cell of the brain and have a different origin to any other brain cell. Microglia are constantly scanning their environment for intruders and danger signals. In case a bacterium or virus enters the brain, microglia are the first line of defence. They can take up and digest bacteria. Not only do they protect the brain from intruders, they also protect the brain from excessive waste. Everywhere in our body, cells die. The brain is no exception from this rule. Dead cells have to be cleared and microglia are really good at eating debris. If there was no one in the brain to clean up like microglia do, neurons and other cells would drown in waste.

I hope this small excursion in the world of brain cells demonstrates what a complicated and refined system is required to allow proper brain functioning. And next time you praise your neurons, maybe it’s time to give your glia cells some recognition, too. Because without their help, we would fall to pieces.