Above: Image © istockphoto.com/DrAfter123
Your head is constantly doing amazing things. For example, as you read the words on this page, your eyes translate the visual information (the letters) into electrical signals, which are then processed by your brain into words and ideas. However, that doesn’t mean your entire brain is dedicated to reading. In fact, your brain is made up of different kind of cells that allow it to accomplish a wide range of tasks. You may even be able to rub your stomach and pat your head (or breathe, beat your heart, and read) at the same time!
Fast Fact: The longest neuron in your body is actually in your leg. The sciatic nerve starts at the lowest part of your spinal cord and stretches all the way to your foot.Of course, your nervous system extends far beyond your head. Everything your body does—walking, talking, grabbing a pencil, typing on a computer—is controlled by your brain. As a result, your brain needs to be connected to all parts of your body. The brain and spinal cord together make up the central nervous system, while the rest of the “brain" cells in your body make up the peripheral nervous system. For example, you have nerves in your legs and arms to help sense motion, react to pain, and control your muscles.
Most of the cells that make up your brain and nervous system are divided up into two main types: neurons and neuroglia.
Neurons, the "thinking" part of your brain and nervous system, conduct electrical impulses containing your thoughts and information gathered by your senses to different parts of your brain. Like all other cells in your body, they contain a nucleus that holds your entire DNA sequence. This part of the neuron is called the cell body.
To help them transmit information to each other, neurons have a long, slender, tail like-projection called the axon. Within an individual neuron, information (in the form of electrical signals) only travels in one direction: from the cell body down the axon.
The rest of the cells in your brain and nervous system are neuroglial cells, which are often simply called glia. Glia cells play different roles and are subdivided into many types. However, regardless of the type, glia cells mainly serve to provide support to the neurons.
Fast Fact: The mirror neuron is a special type of neuron that fire both when you perform an action and when you observe someone else performing the same action. They are what cause you to cringe when you witness an accident.One type of glia is astroglia, which supply nutrients to neurons, provide a structure for neurons to anchor themselves onto, and connect neurons to the blood and chemicals they require. These cells are star-shaped, which is how they got the name astroglia.
Microglia are another type of glia. These cells are much smaller and act as the immune system for the brain and central nervous system, fighting off infections and eating up dead and dying cells. Microglia also release chemicals that can help your brain recover after an injury. Cells called macrophages serve a similar function in your blood.
Oligodendrocytes are yet another type of glia cell. They create the myelin sheath, which is made up of white layers of fat and surrounds the axon. In this way, the oligodendrocytes help speed up the transfer of information between neurons. You can think of it as insulation, like the plastic coating around wire, that prevents the electrical signal from “leaking”.
Your brain and nervous system also contain many other types of cells, including the ones that make blood vessels and cerebrospinal fluid (the liquid shock absorber that your brain floats in), as well as others that help neurons grow and develop.
Although they have learned a lot about the different types of cells that make up your nervous system, and about all the amazing things you can do with your brain, there are still many fundamental things neuroscientists still don’t understand. For example, if reading helps people communicate and stay entertained, no one knows exactly why you sleep. Part of the answer lies in helping the brain clean itself. But the full answer will require an even deeper understanding of how the billions of cells in your brain work together.
Know Your Neurons: What Is the Ratio of Glia to Neurons in the Brain? (Ferris Jabr, Scientific American) Lymphocytes, Monocytes-Macrophages, And Microglia (Dimitri P. Agamanolis, Neuropathology: An illustrated interactive course) Neuroscience Online (Department of Neurobiology and Anatomy, University of Texas Medical School at Houston) Structure and Functions of Nervous Tissue (IvyRose Holistic) What is a Macrophage? (Ananya Mandal, News Medical) What’s so Special about Mirror Neurons (Ben Thomas, Scientific American)
Scholarly publications and textbooks
Kandel ER, Schwartz JH, Jessell TM. 2000. Principles of Neural Science. 4th ed. Prina M, et al. 2014. Microglia: unique and common features with other tissue macrophages. Acta Neuropathologica. Purves D, et al., editors. 2001. Neuroscience. 2nd ed. Sinauer Associates, Sunderland, MA.