In our previous posts, we had started to analyze the brain both from an anatomical perspective and a cellular perspective. As a brief reminder, the brain is composed of cells, mainly neurons and glia. Depending on the method, estimates show that we have approximately from 86 to 100 billion neurons in our brain [1,2].
Neurons are cells that frequently “fire” signals to one another and communicate through synapses* [3]. There are two main types of synapses: electrical and chemical.
In electrical synapses, there are channels between neurons (called gap junctions), which allow fast communication between cells. In fact, ions and molecules can pass directly from one neuron to an adjacent one, allowing the flow of current. Ultimately, this may help to synchronize brain electrical activity [4].
In chemical synapses, a pre-synaptic neuron releases a chemical molecule called a neurotransmitter. This neurotransmitter will travel to the post-synaptic neuron and bind to its membrane-bound receptor, which will then trigger a change in that cell. Depending on the neurotransmitter and the receptor, this can either inhibit or activate the post-synaptic neuron.
Figure 1. Chemical synapse between two neurons [5]
Synapses are the basis of memory processes. In fact, this network of neurons keeps changing and re-wiring due to its plasticity, following the famous Hebbian principle. This principle describes that, when a neuron regularly activates another, causing it to “fire” signals, their connection will be strengthened [6,7].
In summary, neurons are the building blocks of our brain and they “talk” to each other through synapses, which can be chemical or electrical.
*Synapse: refers to a structural gap or junction between neurons that allows the transmission of signals [3].
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Written by: Nicole
Edited by: Natasha
Figure created by: Macrovector (Freepik)
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References:
Are There Really as Many Neurons in the Human Brain as Stars in the Milky Way? | Voytek, B. Brain Metrics - Learn Science at Scitable (2023). Available at: https://www.nature.com/scitable/blog/brain-metrics/are_there_really_as_many/ (Accessed: 4 September 2023).
Azevedo, F.A. et al. (2009). “Equal numbers of neuronal and nonneuronal cells make the human brain an isometrically scaled-up primate brain”, The Journal of Comparative Neurology, 513(5): 532-541. Available at: https://onlinelibrary.wiley.com/doi/10.1002/cne.21974
Südhof T. C. (2021). “The cell biology of synapse formation”, The Journal of Cell Biology, 220(7). Available at: https://rupress.org/jcb/article/220/7/e202103052/212258/The-cell-biology-of-synapse-formationMechanisms-of
Chemical and electrical synapses. Lumen Learning (2023). Available at: https://courses.lumenlearning.com/wm-biology2/chapter/chemical-and-electrical-synapses/ (Accessed: 4 September 2023).
Chemical synapse between neurons. Image by Macrovector on Freepik. Available at: https://www.freepik.com/free-vector/neuroscience-brain-synapse-flat-infographics-with-diagram-scheme-neural-cells-with-text-captions-pointers-vector-illustration_26762581.htm#query=neuron&position=1&from_view=keyword&track=sph
Keysers, C., & Gazzola, V. (2014). “Hebbian learning and predictive mirror neurons for actions, sensations and emotions”, Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 369(1644). Available at: https://doi.org/10.1098/rstb.2013.0175
Morris, R. (1999) "D.O. Hebb: The Organization of Behavior, Wiley: New York; 1949", Brain Research Bulletin, 50(5-6), 437. Available at: https://pubmed.ncbi.nlm.nih.gov/10643472/
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