How the Brain Works

Child Development: Brain Building: Video 1

Narrator: The brain is part of the body’s nervous system. The nervous system is a bit like the body’s control center and communications team. It controls both your voluntary functions, like thoughts and actions, as well as your body’s involuntary functions, like your breathing and heart beating. The nervous system has two main parts: the central nervous system, which is the brain and the spinal cord, and the peripheral nervous system, which includes all of the nerves that carry messages to and from the brain to the rest of the body.

The nervous system is made up of neurons. Neurons are cells that have special features that allow them to quickly send messages throughout the body. There are neurons in the brain – a lot of them. The adult brain has about 86 billion neurons. The neurons in our brains process information coming in from the body through the peripheral nervous system. From this information, neurons form our thoughts and direct our actions.

We also have neurons throughout the rest of our bodies. Some of these neurons sense the surrounding world — the sounds, smells, tastes, textures, touches, and temperatures — and translate these into neural messages that travel to the brain. Other neurons in the peripheral nervous system direct our muscles to contract, allowing our bodies to move and our heart to beat.

Here is a look at some of the special features that enable neurons to send messages throughout the brain and body. Neurons receive signals from other neurons through a network of intake fibers called dendrites. These signals travel down the dendrites in the form of weak electrical currents until they reach the cell body. Once they reach the cell body, these signals, if they are strong enough, trigger the neuron to send, or fire, an electrical impulse. The electrical impulse travels down the length of the neuron’s axon, or output fiber.

At this point, it is important to note that neurons never work alone; each neuron is part of a network of other neurons. Neurons transfer signals to other neurons through structures called synapses. A signal neuron may make thousands of synapses with other neurons. Once the signal reaches the end of the axon, it triggers the release of chemical messengers at the synapse. These chemical messengers are called neurotransmitters. Neurotransmitters travel through the tiny space between neurons and dock in special receptors on the receiving neuron’s synapse. This initiates a weak electrical signal in the dendrites of the receiving neuron and the process begins again. When someone is talking about making connections in the brain, they are talking about synapses. When we learn new information, the number or structure of synapses changes in our brains as a result of repeated experiences.

Many neurons have another feature that helps them to communicate information quickly. The name of this feature is myelin. Myelin is a fatty, insulating layer that wraps around axons. It helps electrical impulses to travel faster down the axon. The brain has many myelinated axons. This allows neurons to rapidly and efficiently communicate.

Zooming back out, this image shows the brain as a whole. The outer part of the brain is called the cortex. The cortex is densely packed with the cell bodies of neurons. The cortex is actually slightly pink in color, but this part of the brain is often called gray matter. It is called gray matter because this dense tissue appears gray in magnetic resonance imaging, or MRI, brain scans.

Beneath the gray matter are bundles of myelinated axons. This is called white matter. The fatty myelin coating on these bundles of axons appears white in MRI scans.

Many axons bundle together to form what are called fiber tracts. These fiber tracts are like superhighways for information, connecting different regions of the brain together. These fiber tracts allow neural messages to travel quickly from region to region.