Neurons and Synapses
A model of half of human brain with a model of neuron to the bottom left of the model brain.
Neurons and synapses. Oh my! Yes, I did go there. Hopefully, you smiled for a quick second. Over the past few weeks, we have spent some time talking about neuroscience, brain structures, etc., but we haven’t gotten to the cellular level to talk about how the brain sends information. Today we are going to rectify this and talk about the cells of the brain and cover a brief introduction about how they communicate.
Chemical Synapse
Let’s begin with the chemical synapse.The synapse is composed of:
Presynaptic ending
Contains neurotransmitters, mitochondria and other cell organelles
Postsynaptic ending
Contains receptor sites for neurotransmitters
Synaptic cleft
The space between the presynaptic and postsynaptic endings.
Neurons are the cells in the brain that are responsible for communication and use both electrical and chemical signals. The neuron's cell body, or the soma, is like other cells, but they are unique in their dendrites and axons. Through the dendrites, cells receive chemical input from other neurons and through their axons communicate to other neurons. The surface of the cell contains an abundance of ion channels that allow small charged atoms to pass through the membrane. One subtype of the channels are the “voltage-gated” channels that allow the neuron to produce the action potential which is the fastest form of intracellular electrical signal conduction in biology (Lovinger, 2008).
As neurons are separated by their outer membranes, there needs to be some way for cells to communicate with each other. This is accomplished through the synapse where chemical interneuronal communication occurs through the release of a substance produced by the soma, the neurotransmitter in a vesicle. The releasing neuron is the presynaptic neuron. The axon terminal of the presynaptic neuron contains vesicles filled with the neurotransmitters clustered in the vicinity of the so-called ‘active zone’ (Nature Structural & Molecular Biology, 2019). When an action potential reaches the axon terminal and a rise in the concentration of calcium stimulates the opening of the voltage-sensitive calcium channels. The increase in intracellular calcium concentration triggers the vesicle fusion and exocytosis and release of the neurotransmitter into the extracellular fluid of synaptic gap between cells. The postsynaptic neuron then senses the released neurotransmitter through different types of receptors like the ionotropic neurotransmitter receptor and the metabotropic neurotransmitter receptors (Nature Structural & Molecular Biology, 2019). There is tight regulation ensuring that the mechanisms are timely, precise, and appropriate.
Electrical Synapse
Forward and onward to the electrical synapse. An electrical synapse is just as important to understand as the chemical synapse. While the chemical synapse transmits via neurotransmitters, electrical synapses share information through ions or charged molecules. This type of synapse is called a gap junction as it is where adjoining cell membranes come together to transmit the ions through opening producing an electrical signal with the ions following from the more positive cell to the more negative cell. This process can only happen when the gap junction is open. The role that this type of synapse plays is more along the lines of excitation of large groups of neurons when they are required to fire at the same time. This type of synapse also plays a role in the developing brain as scientists theorize that gap junctions as they become electrically active at the same time establish chemical connections between themselves. The implication being that gap junctions in the neurons of newborns direct the development of chemical synapses between neurons (Wilson, 2013)
Hopefully, that wasn’t too painful! It is sometimes hard to believe that information in the body is sent via these types of synapses using electrical impulse and neurotransmitters. All these messages that need to be conveyed are sent via molecular processes. It can be mindboggling to think about the amazing things the human body and brain can do!
take action today moment:
Not only can we take a minute to appreciate the amazing things our brains and bodies can do, we can also consider how important it is to take care of our brains and bodies. We ask so much of our brains and bodies on a daily basis, so how can we in turn acknowledge what is accomplished and return the favor. There are many ways to do this including, but not limited to eating a balanced diet that fuels our brains and bodies, acknowledging the importance of mental health, exercising, and the list continues. Make it a point to do at least one thing each day that lets your brain and body know that you appreciate them.
Learn More About neurons and synapses:
Neurons & Synapses (YouTube Video) This one is neat. You get to see actual neurons!
2-Minute Neuroscience: Synaptic Transmission (YouTube Video)
10-Minute Neuroscience: Synapses
References
Alzheimer’s Society. (n.d.). Dementia symptoms and areas of the brain. Alzheimer’s Society.
Armstrong, B. (2018, December 26). How exercise affects your brain. Scientific American. https://www.scientificamerican.com/article/how-exercise-affects-your-brain/
DerSarkissian, C. (2021, August 02). How exercise affects your brain. WebMD. https://www.webmd.com/brain/ss/slideshow-exercise-brain-effects
Intlekofer, K. A., & Cotman, C. W. (2012). Exercise counteracts declining hippocampal function in aging and Alzheimer's disease. Neurobiology of Disease, 57, 47–55. https://doi.org/10.1016/J.NBD.2012.06.011
Lepeta, K., Lourenco, M. V., Schweitzer, B. C., Martino Adami, P. V., Banerjee, P., Catuara-Solarz, S., de La Fuente Revenga, M., Guillem, A. M., Haidar, M., Ijomone, O. M., Nadorp, B., Qi, L., Perera, N. D., Refsgaard, L. K., Reid, K. M., Sabbar, M., Sahoo, A., Schaefer, N., Sheean, R. K., Suska, A., … Seidenbecher, C. (2016). Synaptopathies: Synaptic dysfunction in neurological disorders - A review from students to students. Journal of Neurochemistry, 138(6), 785–805. https://doi.org/10.1111/jnc.13713
Lovinger, D. M. (2008). Communication networks in the brain: Neurons, receptors, neurotransmitters, and alcohol. Alcohol Research & Health: The Journal of the National Institute on Alcohol Abuse and Alcoholism, 31(3), 196–214.
Nature Structural & Molecular Biology. (2019). Neuronal communication. Nature Structure & Molecular Biology 26, 527. https://doi.org/10.1038/s41594-019-0265-3
Wilson, J. F. (2013). Biological basis of behavior. Bridgepoint Education.