The human brain is the most effective known processing unit. It constantly receives and processes numerous signals from both the outside world and our interior. Every day countless processes going on in it, even while we are asleep, engaging 200 billion neurons in complex signal transmission. All these neurons are joined with an incredible number of connections. What makes our excellent processing “machine” so reliable? Let’s take a closer look at the principle of its operation.
Brain – artistic impression. Image credit: geralt via Pixabay, free licence
The brain is the most complex and fascinating human organ. Its structure is about 60 percent fat, and the rest is a combination of water, protein, carbohydrates, and salt. In addition to receiving signals from the outside world, our brain performs countless tasks, including controlling the vital human signs such as body temperature, blood pressure, heart rate, and breathing.
Thanks to it, we think, dream, and feel emotions. We can say that it works like an extensive and highly efficient computer. If we look deep into this fantastic machine, it is made up of tiny computing units called neurons. Each of them is connected to the other branches making complex connections so that the brain can do extraordinary things. Well, maybe not every brain, but the vast majority of them.
What about the processes in our brain, and what biological and chemical processes are behind the fact that we think and we can do so many things? Let us consider together why we are so unusual from the point of view of biology, chemistry, and neuroscience.
Information flow in the brain
Information is the most valuable thing in the world. Every day our brain is distracted by countless amounts of information in the form of sounds, images, and texts. How is it that we can perceive and understand them? We owe everything to an intricate network of neurons, which process nerve impulses.
Neurons communicate with each other through electrochemical signals. When a neuron receives such a signal, it releases stored information carriers in the form of molecules called neurotransmitters. We distinguish five main groups of neurotransmitters: amino acids, biogenic amines, neuropeptides, adenosine, and gas relays. First, we can split into two subgroups: the aromatic (tryptophan, tyrosine, phenylalanine) and the acidic amino (glutamate and aspartate) acids.
The aromatic amino acids are our source of energy and are responsible for the homeostatic function (maintaining the stability of various internal variables, including temperature and environmental changes) of brain cells. Tryptophan is converted into serotonin, which is responsible for our mood, regulates appetite, pain sensation, sleep and wakefulness, the processes of learning and remembering, and affects the functioning of the human digestive system.
Tyrosine is essential in the production of epinephrine (in emergencies, it plays a significant role in the immediate response of the body), norepinephrine (mobilizes the brain and body to act), and dopamine (responsible for energy, well-being, and motivation to action). It is involved in the production of melanin, the pigment responsible for hair and skin color. It is involved in the production of every protein in our body.
Phenylalanine is used to produce proteins and signaling molecules. Acidic amino acids actively take part in the synthesis of proteins. Glutamate is a component of 90 percent nerve cells. The functioning of the brain depends on its level. Too low glutamate’s level leads to the death of neurons.
As a consequence of many neurological diseases, the role of aspartate remains a mystery. The second group of neurotransmitters includes catecholamines, dopamine, and norepinephrine. They are responsible for many brain functions such as motor control, cognition, emotions, memory processing, and hormone modulation.
Norepinephrine helps us wake up, focus on various activities, and it is responsible for memory storage. It is released in stressful situations and when receiving various stimuli and helps organize the work of neurons in response to the information provided. Catecholamines take part in our cognitions and memory processes, motor and emotional control.
Our neurons use neuropeptides to communicate with each other. They also help regulate metabolism, learning, and reproduction. Adenosine helps to calm down the body and to fall asleep. It can act as a depressant. Lastly, gas relay neurotransmitters play an important role in brain control. As you can see, the information transmitted in our brain requires complex biochemical processes engaging multiple molecules in it.
Communication between brain and body
In addition to the nervous system (neurons), the endocrine system plays a vital role in the communication of our brain and body. Its role is the production and secretion of certain chemical compounds – hormones. Hormones are produced by organs such as the pancreas, kidneys, heart, adrenal glands, gonads, thyroid, parathyroid glands, thymus, and even fat.
Hormones help the brain grow and develop, and this process begins in the womb. During the first year, brain size grows three times. They regulate appetite, digestion, sleep rhythm and affect many other aspects, such as our mental health. Their action can be compared to traffic lights at a considerable junction – they are therefore essential, and in case of their disorders, the whole organism malfunctions. Hormones' principle of operation consists mainly in acting on neurons, which regulate the pituitary gland (part of the brain, which different substance into the blood).
Neuroplasticity
The brain constantly develops new neural connections. Moreover, it produces more neurons based on our choices and experiences, e.g., while doing some mental exercises or training yoga. There are many more examples of brain training that stimulates it to produce more specific neurons.
Without stimuli, fewer neurons are formed, and the neural network is less branched; while constant brain stimulation by a particular activity, more neural connections are formed leading to the thriving neural network looking like a tree with new branches. It is called neuroplasticity that in other words, is the adaptation of neurons to a new situation.
Interesting non-obvious facts about the human brain
- When we consider brain structure, blood vessels present in the brain are almost 160,000 kilometers long. The speed of the nerve pulse is about 400 km/h.
- When you are not sleeping, your brain generates about 25 watts of energy, which is enough to light up the light bulb.
- It is only about 25 years of age that the human brain reaches full maturity.
- After reaching middle age, our brain size decreases.
- The brain is not multitasking at all. Even when we work multitasking, we switch quickly between tasks but still perform one task.
- When we are very tired, we are more creative. It sounds ridiculous, but it's true. When we are tired, our brain is tired. Its efficiency drops, which translates into worse filtering out disturbances, difficulty focusing on a specific task, and weakening of remembering connections between ideas. Moreover, this makes our brain more receptive to creative thinking.
- Everyone knows that stress harms health. However, not all of us are aware that a large amount of stress can reduce the size of our brains.
- Short naps improve brain performance.
- We have several sense organs, including hearing, sight, taste, smell, touch, and balance, while the sense of sight has the most significant influence on the brain.
- The size of the brain has nothing to do with the level of intelligence. For example, sperm whales have a brain five times the size of a human, and humans have a much higher level of intelligence. In measuring intelligence, the ratio of brain weight to total body weight is essential. This measure is also not perfect because, in the general classification of humans, it is ahead of the shrew. Furthermore, that is not entirely true about its level of intelligence.
- The brain cannot sense pain; it only interprets pain signals that reach it.
Summary
We dare to say that the brain is our central control unit. It is divided into two not entirely equal hemispheres. The right side regulates the left side of the body, and the left side regulates the right side. One hemisphere is slightly dominant, which affects, among other things, right-handedness or left-handedness. The brain's left hemisphere is associated with linguistic abilities and logical thinking, while the right has creativity and artistic abilities. The proper functioning of both hemispheres is not possible without the appropriate level of various neurotransmitters and hormones.
This article is a joint work of Aleksandra Chrząstowska (Faculty of Chemistry, University of Warsaw), Oliwia Raniszewska (Faculty of Chemistry, University of Warsaw), Agnieszka Pregowska (Institute of Fundamental Technological Research, Polish Academy of Sciences; Faculty of Chemistry, University of Warsaw), and Magdalena Osial (Faculty of Chemistry, University of Warsaw; Institute of the Fundamental Technological Research, Polish Academy of Sciences; and Extremo Technologies) as a part of the Science Embassy project. Image Credit: Magdalena Osial.
REFERENCES
Fernstrom JD. Dietary amino acids and brain function. J Am Diet Assoc. 1994 Jan;94(1):71-7. doi: 10.1016/0002-8223(94)92045-1.
Fernstrom JD, Fernstrom MH. Tyrosine, phenylalanine, and catecholamine synthesis and function in the brain. J Nutr. 2007 Jun;137(6 Suppl 1):1539S-1547S; discussion 1548S. doi: 10.1093/jn/137.6.1539S.
van Spronsen FJ, Hoeksma M, Reijngoud DJ. Brain dysfunction in phenylketonuria: is phenylalanine toxicity the only possible cause? J Inherit Metab Dis. 2009 Feb;32(1):46-51. doi: 10.1007/s10545-008-0946-2.
Zhou Y, Danbolt NC. Glutamate as a neurotransmitter in the healthy brain. J Neural Transm (Vienna). 2014;121(8):799-817. doi:10.1007/s00702-014-1180-8
Herring BE, Silm K, Edwards RH, Nicoll RA. Is Aspartate an Excitatory Neurotransmitter?. J Neurosci. 2015;35(28):10168-10171. doi:10.1523/JNEUROSCI.0524-15.2015
Kobayashi K. Role of catecholamine signaling in brain and nervous system functions: new insights from mouse molecular genetic study. J Investig Dermatol Symp Proc. 2001 Nov;6(1):115-21. doi: 10.1046/j.0022-202x.2001.00011.x.
Haskó G, Pacher P, Vizi ES, Illes P. Adenosine receptor signaling in the brain immune system. Trends Pharmacol Sci. 2005;26(10):511-516. doi:10.1016/j.tips.2005.08.004
Ufnal M, Sikora M. The role of brain gaseous transmitters in the regulation of the circulatory system. Curr Pharm Biotechnol. 2011 Sep;12(9):1322-33. doi: 10.2174/138920111798281126
Ali SA, Begum T, Reza F. Hormonal Influences on Cognitive Function. Malays J Med Sci. 2018;25(4):31-41. doi:10.21315/mjms2018.25.4.3