The blog “A Plastic Journey: Introspection of Brains Learning About Brains” delves into the qualia, feelings and thoughts brought forth in the authors’ brains upon learning about the human brain and its functions. The blog will follow loosely the structure of the course “NBE-E4210 – Structure and operation of the human brain.” The blog is written in the form of a fact-filled, loopy and introspective story. [Logo: Oxford University Press (2018).]
Chapter 15 was extremely interesting. When the focus is on hypothalamus, autonomic nervous system and diffuse modulatory systems, countless important functions of human life from appetite to motivation and from sex drive to blood pressure start to emerge. This is the area where so many things we would like to be able to control are found, and effort hasn’t been spared either. We often eat too much and crave unhealthy food, and sleepiness gets in the way of night time military operations and studying neuroscience. We also have an ever growing list of substances that are cultivated, prescribed, bought and sold to control the chemicals that control us.
All three systems discussed in chapter 15 have one common basic role: maintaining the brain homeostasis. Homeostasis is the process where brain controls the body’s internal environment like blood pressure, body temperature and glucose concentrations to be compatible with the ever changing external circumstances. Hypothalamus is located below thalamus and along the walls of the third ventricle. Often described as being about the size of an almond, hypothalamus makes up less than 1 percent of the brain mass but its influence on our body physiology is e enormous. Even a small damage to this tiny part of the brain can cause fatal disruptions to our most important bodily functions.
Some especially interesting parts of the chapter included the two details about food and the brain: Enteric division of the ANS and the connection between our diet (like carbohydrates and protein) and the serotonin levels in brain.
Frequently discussed in popularised science articles and podcasts, enteric division is at the same time both fascinating and strange. It consists of two networks with a total of 500 million neurons, which is as much as in the spinal cord. It quite independently (from both symphatetic and parasympathetic nervous systems) controls and monitors things like the transport and digestion of food, chemical status of stomach and hormonal levels in blood, so it’s no surprise it’s sometimes referred to as our “second brain”. Even the neurotransmitters in CNS and enteric system are mostly similar. One of them, serotonin, is linked with our diet in interesting ways.
Like we learned last week when talking about neurotransmitter systems, serotonin, one of the amine neurotransmitters important for many functions from intestinal movements to our mood, is derived from the amino acid tryptophan via a two-step synthesis process. This means the serotonin levels in the brain are limited by the availability of tryptophan in blood, which in turn depends on our diet. The paradoxal process involving other competing amino acids, insulin and blood-brain barrier results in interesting findings, like that reduced daylight during winter makes us crave for carbohydrates and that same serotonin-elevating drugs can help a person with both weight loss and depression.
This underlines the idea that it’s not rational to view a human being as a dualistic combination of “body” and “spirit”. We think and how we eat, and we eat what we are made of. Sleeping too little, feeling happy or cold, being in love, choosing low carb over low fat, it’s all connected.