The Science Vista

(Illustration: Francesco Izzo) "Like stars in the Milky way..." This phrase is often used because it is so difficult to give people a sense of scale when it comes to large numbers. That's why you would have seen articles reporting distances as the number of tennis courts, mass as the number of vehicles, etc. Even though the number of stars and neurons have not been proven to be precisely the same, equating the two gives a sense of enormity. It is human nature to find patterns, equate things and refer to relatable examples, which is why neurons are often compared to stars. These cells are responsible for everything we do. In fact, the human brain is literally one of the most complex structures known in the universe. The latest estimate is that the brain contains roughly 86 billion neurons. These cells process input from the senses and send signals to your body through the nervous system. Each neuron connects to about 10,000 other neurons through synapses. As a result, over 100 trillion connections between neurons form the neural network that creates who we are. A helpful analogy is to think of a neuron as a tree. It has three main parts: dendrites, an axon, and a cell body or soma, which can be represented as the branches, roots and the trunk of a tree respectively. A dendrite is where a neuron receives inputs from other cells. Dendrites branch as they move towards their tips, like tree branches. Just like trees, they even have leaf-like structures called spines. The axon is the output structure of the neuron; for communicating with another neuron, it sends an electrical message called an action potential throughout the entire axon. Finally, the soma is where the nucleus is present, and proteins are made for the normal functioning of the neurons. When the action potential reaches the axon terminal, some of the neurotransmitters in the terminal are released into a tiny gap between the terminal and the dendrite of another neuron. This gap is called a synapse. The neurotransmitter crosses the synapse and binds to a receptor on the other side. Each neurotransmitter binds to its specific receptor, just as a key fits only in a particular lock. Then, depending on the neurotransmitter, it either stimulates the other neuron or inhibits, making it either more likely or less likely to fire an action potential of its own. All these happen with very high precision and are repeated again and again. It is almost as if the neurotransmitters pass secrets directly from one neuron to another. The exact location can be reached via multiple routes and vehicles. The same is the case with neurons. In addition to neurotransmitters, neuropeptides are also released from many parts of a neuron, including the dendrites. Rather than being released into the tiny synapse between an axon terminal and another neuron, they are released into the fluid that fills the spaces between neurons. They diffuse through the brain to reach receptors on distant targets. Think of it like a hiker making way through a dense forest. To go from one point to another in the absence of trees would have been easier. However, due to the density, this type of signaling is much slower than signaling at synapses, but eventually, the neuropeptides will reach most parts of the brain. However, only brain areas with the right receptors can respond to the neuropeptides. If you have stuck around till the very end, here's an interesting tidbit: The brain generates about 20 watts of electricity. This is enough to power a low-wattage light bulb! Well, it is time to bid adieu, but I hope you continue learning more exciting facts about neurons, stars, and much more! Until next time. Author: Shreya Ahuja Editor: Himanshi Yadav