Neurons

The brain is comprised of neurons and glial cells. Most people have heard of neurons, and most neuroscience research focuses entirely on neurons, neural communication, and networks of neurons. Why? Neurons are exciting...and glial cells (every bit as exciting) were once thought to have little function and only provide structure for neurons.  For now, we'll focus the anatomy of neurons and how it relates to their function and later we'll dissect the components and types of glial cells.

Let's start with neuronal structure. There are several ways to classify neurons, but I find that it is easiest and also most intuitive if we focus on whether the neuron is unipolar, bipolar, or multipolar. Don't be alarmed! Simple count the number of connections the cell body has. If it has one, it is a unipolar neuron. If it has two, it must be bipolar. Three or more and it is a multipolar neuron.

Most neurons have the same physiological makeup. Let's start with a signal arriving at the neuron and progress until the neuron passes the message to the next neuron.

• Dendrites: These branchy parts are responsible for receiving the communication from other neurons.
• Cell body (soma): The part of the neuron that houses the nucleus and other important cellular organelles.
• Axon: All the information from the dendrites and cell body is passed along to the next neuron via this slender extension. Sections of the axon are wrapped in 'insulation' or myelin that act to speed up the electrical communication as it travels down the axon.
• Terminal buttons: At the end, the axon branches out to neighboring neurons and forms synapses (tiny space between neurons). The terminal button contains vesicles (tiny packages of chemicals), protein receptors, and transporters. This area is critical for neural communication.

The dendrites receive the signal, the cell body integrates the signal, the axon is the avenue that carries the signal, and the terminal buttons pass the signal to the next neuron with neurotransmitters. Those little packages in the terminal buttons are filled with neurotransmitters. If the neurotransmitter excites, then the probability of an electrical signal being passed to the next neuron increases. If the neurotransmitter inhibits the probability of an electrical signal reaching the next neuron is reduced. All of this is done extremely fast through electrochemical communication...Neurotransmitters are chemicals that change the probability of electrical communication. 

Again, these are the beginnings of understanding how neurons communicate, form circuits, and change behavior.