Brain Basics: Neurons
Neurons are the elementary units of the brain and overall nervous system. Neurons, also called nerve cells, are similar to other cells in the human body in that they have a nucleus, which holds the genetic information, and they contain organelles, such as the Golgi apparatus, mitochondria, and cytoplasm, which support the life of the cell. However, neurons also have unique structures, such as axons and dendrites, that are designed to transmit and receive information. Although there are different kinds of neurons, all neurons have three basic parts:
- The Dendrites
Dendrites are short, highly branched extensions at the beginning of a neuron that extend outward from the cell body. These dendrites are responsible for receiving chemical signals from other neurons, which are then transformed into electrical impulses and transmitted to the cell body. There is a lot of variability in the number and size of dendrites that a neuron has. Most neurons have many dendrites, which enhances neural communication, but it is also possible for a neuron to have only one dendrite.
- The Cell Body
The cell body, also called the soma, is where the nucleus and other organelles are located. These organelles are responsible for keeping the cell alive. The cell body is also where proteins are synthesized and sent to other parts of the neuron, where energy is produced, and where chemicals are packaged and prepared for “dispatch”. The electrical impulse generated by the dendrites is sent through the cell body before reaching the axon.
- The Axon
The axon is a single, elongated fiber extending from the cell body to the terminal ending. The axon is responsible for transmitting a neural signal (i.e. information) in the form of an electrical impulse, called an action potential. The speed of neural communication depends, in part, on how fast a signal can travel down the axon. In general, the larger the diameter of the axon, the faster the signal can travel. In some cases, the axon is covered with a fatty substance called myelin, which acts like an insulator and speeds up communication. Every neuron has only one axon, which branches at the end, forming axon terminals. Axons can be as short as 0.1 millimeters or as long as 3 feet*.
*FUN FACT: The longest axon in the human body extends from the bottom of the spine to the big toe and averages approximately 3 feet long.
Brain Basics: The Synapse and Synaptic Transmission
A synapse is where neurons are able to communicate with each other, or with other cells in the body. Neurons are not actually connected to each other, but are separated by a tiny space, called the synaptic cleft, which is less than 20-40 nanometers wide. For comparison, an inch is about 25.4 million nanometers long. Neurons communicate with each other via chemicals, called neurotransmitters, that are packaged in vesicles and sent across the synaptic cleft. Vesicles are released from the axon terminals of the first neuron (the presynaptic neuron) and interact with receptors on the dendrite of the second neuron (the postsynaptic neuron) by binding to the membrane. The postsynaptic neuron can then transform this chemical signal into an electrical impulse that gets transmitted to the cell body and eventually travels down the axon to the next neuron and so on and so forth.
NOTE: This is an incredibly simplified explanation of neurons, synapses and synaptic transmission. Neural communication is a very complex concept involving action and membrane potentials, many different chemical messengers, factors that inhibit or facilitate communication, thresholds, and so much more. This information has been distilled to the most basic concepts for clarity.
What is Neuroplasticity?
How is neuroplasticity related to health, wellbeing and learning?
Get a head start on leveraging your brain’s plasticity for the better by watching Dr. Lara Boyd’s TEDx Talk, “After watching this, your brain will not be the same”.
Where can I learn more?
What will students learn?
By the end of this lesson, students will be able to…
- Recognize and appreciate the complexity of the human brain
- Describe the three main parts of a neuron as well as the basics of synaptic transmission
- Understand that the brain changes in response to repetitive behaviours, thoughts and emotions
- Apply their knowledge to leverage neuroplasticity to change themselves and their life for the better
Demarin, V., Morović, S., & Béne, R. (2014). Neuroplasticity. Periodiocum biologorum, 116(2). 209-211.
McGill University. (2014, May 28). Scientists control rapid re-wiring of brain circuits using patterned visual stimulation. ScienceDaily.
Queensland Brain Institute. (2018, April 17). What is Synaptic Plasticity? The University of Queensland Australia.
Boyd, L. (2015). After watching this, your brain won’t be the same [video]. TED.