The brain is a complex communications network of billions of neurons, neurotransmitters, and receptors. Networks of neurons pass messages back and forth thousands of times a minute within the brain, spinal column, and nerves. These nerve networks control everything we feel, think, and do. For example, when you want to go up the stairs, this message system will tell you to lift your foot onto the first step and so on. Understanding these networks helps scientists learn how drugs affect the brain. The networks are made up of:
Your brain contains about 100 billion neurons—nerve cells that work nonstop to send and receive messages. Within a neuron, messages travel from the cell body down a nerve fiber called an axon in the form of electrical impulses. From there, the message is sent to other neurons.
- Neurotransmitters—The Brain's Chemical Messengers
To help those messages travel from one neuron to another, the brain creates chemical messengers called neurotransmitters. Branches of the axon, called axon terminals, release neurotransmitters into the space between two nerve cells, called a synapse. The axon terminal is like the bus or train terminal - a transportation hub of activity.
- Receptors—The Brain's Chemical Receivers
As the neurotransmitter approaches the nearby neuron, it attaches to a special site on that neuron called a receptor. A neurotransmitter and its receptor operate like a key and lock--- a very specific mechanism makes sure that each receptor will forward the right message only after interacting with the right kind of neurotransmitter.
- Transporters—The Brain’s Chemical Recyclers
Once neurotransmitters do their job, they are pulled back into their original neuron by transporters. This recycling process shuts off the signal between the neurons.