Neuronal firings come to mind when we consider the brain and how it functions. However, how precisely does our brain produce these messages, and how do they interact? "Synaptic transmission" is a term you may hear a lot when learning about brain communication. Our brain and body work, remain healthy, and are in good condition thanks to the transfer of information from one neuron to another, which is implied by the term itself. Our nervous system's electrical signals are essentially its language. The neurochemistry that underlies this communication is synaptic transmission which is concerned with the interaction of the chemical substances involved. Here is an in-depth overview of all you need to know about neural communication from one neuron to another.
The signal that ultimately causes a neuron to fire originates in the axon hillock, where it is first produced. When a stimulus shifts the membrane potential to threshold potential, an action potential is swiftly created. An electrical impulse or action potential can be produced by a stimulus with a threshold electrical value. This action potential develops and travels along the axon at a high speed. An insulating layer is developed surrounding the axon to help it carry electrical impulses more effectively. Other neurotransmitters are released as the impulse enters the axon terminal, converting it into a chemical signal for the following cell. Now, the information stored in the signal is getting ready to be transmitted, but there are some crucial steps just before it can get there!
Ion channel receptors allow calcium ions to enter the axon terminal as the axon terminal depolarizes. The synaptotagmin protein attracts the calcium ions as they enter. This protein uses calcium ions to produce vesicular exocytosis. A synaptic vesicle must fuse with the pre synaptic membrane during the process of exocytosis in order to release the substances that it is holding. Two more specialized proteins work with synaptotagmin to fuse the presynaptic membrane and synaptic vesicles. A protein known as v-SNARE is bound to the synaptic vesicle itself. Another protein that binds to the presynaptic membrane is the t-SNARE. The v & t - SNAREs start to entangle as the synaptotagmin draws calcium. They do this by lowering the synaptic vesicle toward the membrane and joining them. The full fusing procedure is depicted in the diagram below:
The diagram displays the pathway of the electrical impulse to a chemical signal and its fusing of the membrane to the vesicle, from https://ib.bioninja.com.au/standard-level/topic-6-human-physiology/65-neurons-and-synapses/synaptic-transfer.html
Neurotransmitters are released once the vesicle and membrane have joined. They pass across the synaptic cleft, which is the opening between one neuron's axon terminal and its dendrites.Scientists have discovered that neurons truly have this minuscule space—known as the synaptic cleft—between them rather than being physically connected. As soon as these neurotransmitters reach the synaptic cleft, they bind to receptors on the dendrites of other neurons. As the neurotransmitters attach to receptors on the postsynaptic membrane, the dendrites will take in the information, generate more action potential, and process it. However, sodium ions will start the action at the relevant neurons producing action potentials.
The brain understands how much of each neurotransmitter it needs and doesn't require, so if there are too many neurotransmitters in the area, enzymes will break them down. The brain uses an endocytosis process to determine if the neurons can still be regenerated. Synaptic vesicles are recycled during endocytosis so that the neuron can repurpose them, fill them with neurotransmitters, and then repeat the process. This is the brain's method of maximizing its resources.
The synaptic transmission process is a very fascinating and intricate one. There are an endless number of receptors, neurotransmitters, and chemical names. Such procedures demonstrate the complexity of the connections that our brain is capable of forming. But why is it so crucial to understand this? Numerous neurological conditions may be related in some way to the brain's synaptic transmission system. This process supports a variety of important daily skills like memory, learning, and cognitive function. Therefore, it is extremely important to understand this process since it directly impacts our lives in ways we cannot imagine.
Resources:
Action potentials and synapses. Queensland Brain Institute - University of Queensland. (2023, April 26). https://qbi.uq.edu.au/brain-basics/brain/brain-physiology/action-potentials-and-syn apses
Khan Academy. (n.d.). The synapse (article) | human biology. Khan Academy. https://www.khanacademy.org/science/biology/human-biology/neuron-nervous-sys tem/a/the-synapse
Synaptic transmission - basic neurochemistry - NCBI bookshelf. (n.d.). https://www.ncbi.nlm.nih.gov/books/NBK27911/
Synaptic transmission. Synaptic Transmission - an overview | ScienceDirect Topics. (n.d.). https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/synaptic transmission
W;, V. (n.d.). The synaptic vesicle and its targets. Neuroscience. https://pubmed.ncbi.nlm.nih.gov/7700521/
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