Disclaimer to this essay – all opinions and expressions in this article are by the gray matter of the Cerebral cortex up in my head and I am not personally responsible for any omissions and commissions herein!
Whenever we refer to the awesome portrayal of the human brain, let me emphasize we are talking of the Cerebral cortex in particular. The prowess of human brain has greatly mystified our curious minds scientifically, spiritually, philosophically and literally. Behind all these paeans of the human brain is it’s the exceptionally and relatively large (in terms of brain-body ratio) mass of gray and white matter up in our heads called as neo-cortex. The nervous system is not unique only to human species nor is the structure of the central nervous system in particular. It is this Cerebral cortex that makes us humans stand apart in the animal kingdom. We do have highly developed language (both spoken and written), we do politics, we celebrate Diwali and Dusshera, we fight wars with guns and nuclear bombs over imaginary lines called international boundaries (and occasionally with finger nails and teeth), we bore ourselves in the classrooms and we even tame other animals for our own needs. This essay is a reflection and analysis of the remarkable abilities of this part of animal body and the way it has shaped our own history and that of the planet as well. This is a ‘semi-scientific’ account of cell politics on earth and the way the brain has come to dominate all tissues eventually though not finally.
Cells in our world are divided in to two basic types, prokaryotic and eukaryotic. Between them a few million different types have been counted. Each one has evolved in its own unique ways; some have evolved as unicellular while others as multicellular. The multicellular organisms then differentiated as plants and animals sometime in the time-line of evolution. The respective cells also evolved accordingly in the multicellular system and so we have an array of plants and animals ranging from the Ferns to Banyan and Hydra to Humans. This diversity that we see today was not an overnight event, it took millions of years to get to this and in these millions of years a fascinating story unfolded. This article is about that story albeit from the perspective of the animal kingdom. In higher life forms, cells are organised as tissues and then organs. In the animal kingdom, tissues are grouped into four basic types: connective, muscle, nervous, and epithelial. The human body alone has between 50 and 75 trillion cells divided into these basic tissue types. So we have muscles – cardiac, smooth and skeletal, blood cells – mast cells, lymphocytes, basophil, neutrophil, eosinophil, monocyte and erythrocytes, adipose cells, neurons, mucous cell, serous cell, sweat gland cells – dark and clear, lacrimal gland cell, Prostate gland cell, gastric gland zymogenic cell, Clara cell and pneumocyte in lungs, cells of thyroid - thyroid epithelial cell and parafollicular cell, Leydig cell cell of testes, corpus luteum, Granulosa lutein cell and theca lutein cell of the oaries, endothelial fenestrated cell, endothelial continuous cell and endothelial splenic cell lining the blood and lymph vessels, Medullary hair shaft cell, Cortical hair shaft cell, Cuticular hair shaft cell, Cuticular hair root sheath cell, so and so forth. Discussing all these cells is beyond the scope of this article. Never-the-less all these cells are vital to the survival of an organism and hence they all evolved in ways to be what they are today.
While the story of evolution unfolded some of these cell types have made a niche for themselves in ways so unique, it is the subject I am interested in. Just as in our society, people go about their various jobs contributing in their own ways to run the system – the plumber to policeman, the rock star to teacher, the bus driver to poet and electrician to politician. While all of them are important in order for a society to function smoothly, some amongst these do make a greater difference and they are the ones whose contributions become crucial to changes in the society. That’s what differentiates them from the ordinary. So while most people go about their daily business, these men do something significantly different.
“Peter Not everyone is meant to make a difference. But for me, the choice to lead an ordinary life is no longer an option."
- Spiderman
The multicellular system can also be seen as society wherein many cells just go about the usual house keeping functions but some have exceptionally stood out in to change the course of life of an animal. Savour this, in 2003 US invades Iraq on the issue of weapon of mass destruction (WMD) issue and thousands of lives perish. The occurrence of that one event entirely depended on one human being – George Walker Bush, the then President of United States of America. That one event took the lives of thousands, wiped out a political regime that had ruled a nation for 35 years, destabilized several neighbourhoods, brought to fore communal and ethnic conflicts in an other wise liberal-minded populace, so and so forth. That one event changed the lives of a million people. That one event started not from the hepatocyte, erythrocyte, megakaryocyte, monocyte, Langerhans cell Paneth cell, Oxyphil cell or Chromaffin cell of Mr. George Walker Bush. That one event didn’t start from the liver, pancreas, kidneys or bones of Mr. George Walker Bush. It started from his head, his brain and in particular the Cerebral cortex somewhere in its gray matter. These are the otherwise inconsequential elongated strand like cells we peep down the tubes of our microscope – the neurons. So you see a great and significant event of our history was the handiwork an otherwise inconspicuous and unassuming cell called neurons. This particular cell has been singly responsible for almost everything in the history of mankind – from nations going to war to peace treaties, from invention of atom bomb to discovery of penicillin, from Romeo and Juliet to Rasputin and Nicholas II, from colonialism to liberalism, from Mein Kampf to the Communist manifesto and from Judaism to Hinduism.
In order to understand this astonishing cell type, let us do a little flashback on its humble beginnings. Sponges are a tube-shaped primitive group of animals belonging to phylum Porifera. The sponge has no nervous system and considered simplest of all animal species. The simplest nervous system can be seen in a Hydra, a microscopic fresh-water organism belonging to the phylum Cnidaria and the class Hydrozoa. This animal can sense light, has tactile sensation and can retract its tentacles as well as body when threatened and locomote in a somersaulting fashion. However the organism reacts in the same way no matter which direction the stimuli comes and what type of stimuli. Compare this to human beings; we react to the same stimuli say a verbal communication in 100 or more different ways! This is to illustrate how the evolution of nerves and nervous system has come a long way. Another animal which has a simple nervous system is the Jelly fish, members of the phylum Cnidaria. The Jelly fish also doesn’t have a proper nervous system but rather a loose network of nerve cells interconnected to each other to form a “nerve net”. The nerve net is responsible for automated and coordinated movement of its skirt that is powers its locomotion. The Jelly fish can sense light and tactile stimuli. The strength of its response is proportional to the stimulus strength i.e., stronger the stimulus, stronger the response. There is no analysis of the incoming stimuli. Contrast this to Human behaviour wherein sometimes we punch back if we are punched (your little brother) and sometimes you just keep quite (your class bully). Therefore, analysis and processing of incoming stimuli and the response is a feature of higher animals. The simplest true nervous system can be seen in the planarians, the slimy flatworms which make many people quiver and are found beneath rocks, logs, or dead leaves. The nervous system in these organisms exhibit encephalization in that they have a simple brain composed of a cluster of neurons or ganglia. From then onwards we see more and more complex nervous system as we move from Annelids, arthropods, and molluscs to mammals.
From all this its evident that nerve cells originally evolved in order to enable a multicellular organism to detect stimuli and then cause the organism to respond accurately. Along the evolutionary timeline, this basic purpose became more and more fine tuned and that explains the difference in the compulsively same responsive behaviour of a Hydra to all stimuli and the varied responses if Human beings to the same stimuli. So between Hydra and Human beings what significant property of the nerves and nervous system changed? The answer is faster conduction and the ability to analyse and process both incoming stimuli and outgoing signals for response. This particular ability of the higher animals, especially human beings is what we psychologically and philosophically call ‘the mind’. That makes the cortical tissue, primarily the neurons the most formidable cell amongst all animal tissue cells. Thus, when Alexander the great, moved his mighty army from Macedonia to overrun kingdoms from Mediterranean Sea to India, the tiny gray coloured cells up in his cortex was working over-time. When Hitler enthralled the Nazi party with bombastic speeches and hypnotised his party workers to fanatically hate the Jews, his intestines had nothing much to do with it. When Enrico Fermi, widely known as “the father of atom bomb” devised the first controlled nuclear fission paving way to the development of atom bomb, the alpha cells of his pancreas didn’t take any part. Celebrated scientist, known of his revolutionary special and general theory of relativity is famous for his brain, not for his bones. When Mikhail Timofeyevich Kalashnikov designed his deadly AK-47 (favourite of warlords world over), it’s the neurons up in his head that conjured up the idea while the synovial cells in his joints were secreting lubricants to avoid locking of his joints.
However it doesn’t end here, there is more in store from this unassuming cell. The Cerebral intentions are most evident in human beings as it has achieved the highest phylogenetic development in this species. So what began as simple mechanism for environmental assessment and to respond accordingly, now has sinister plans. One other rival cell to the neurons in being that “Spiderman” (see quotes above) in the animal world is the skeletal muscle cell. This rivalry of kind will be explained later in this essay. So first in the line of fire of the neurons was the skeletal muscle. This is evident from the invention of tools. By inventing tools the neurons are attempting more and more to circumvent the need of the muscle cells to provide any mechanical function. Mechanical work through muscles means more nerves need to fire up and this is what we sense an effort while lifting a heavy suitcase or pushing a boulder. As you increase your effort while lifting a heavy load, more and more motor units (that consists of a group of skeletal muscles connected to a motor neuron) are activated, a process physiologically known as ‘Recruitment’. An effort also involves increased frequency of firing by the motor neurons which we sense as a feeling of disdain to do physical labour and hence the famous proverb “no pain, no gain”. So in order to relieve itself of this ‘pain’, the Cerebral cortex first invented simple tools such as a crow-bar to lift and push heavy loads. Then there is the effort we put to move from one place to another, so the Cerebral cortex invented automobiles such that our dependence on leg muscles has reduced considerably (bye-bye Gluteus maximus, Quadriceps and Hamstrings). Even walking came to be perceived an effortful activity and so the Cerebral cortex in some person’s head came up with the idea of Segway Personal Transporter. Muscles are also critical to one’s own protection as it gives us physical power to fend off an adversary (and also enables us to bully others) but then the Cerebral cortex invented weapons to obviate the need for muscles for self-defence or attack. The David-Goliath story is an obvious illustration of brain over brawn. Thus, the Cerebral cortex has circumvented the need for muscle cells on several fronts. On the front of gross motor activity, this circumvention is totally complete. Even on the fine motor skills, the Cerebral cortex has been able to circumvent its functions with the invention of robots and other electronic gadgets. The only major front in which the Cerebral cortex has not been able to circumvent the need for muscles is surgery. The technological advancement in this field is still in budding stage. Ironically, it still doesn’t want to take chances with its own creations when it comes to its primeval fear of dying!
It’s not just the skeletal muscle that is being targeted by the Cerebral cortex (neurons in particular). Gradually more and more tissues are coming in the ‘hit list’ of the neurons and there is growing tendency to do away with them. So today we have an assortment of artificial food supplements from Horlicks, Complan to vitamin capsules. That means the Cerebral cortex is intending to do away with many of the cells lining the gastrointestinal tract that are responsible for digestion process. Though the idea to circumvent the need for digestion process may seem an impossible scheme at present, it’s not something impossible. The tablets and capsules of vitamin and minerals certainly are able to meet our nutritional needs to some extent while the intravenous infusion of Ringer Lactate solution directly augments the blood volume without the route of the gastro-intestinal tract. Though present technology is far too incapable and inefficient to replace any of the bodily functions entirely, it’s not hard to contemplate that entirety will be achieved in years to come. Thus, heart-lung machine which is used for bypass surgeries can do what the cardio-pulmonary system does. Though, the limitations of present technology require that the machine is a bulky one, someday we can have a pocket sized heart-lung machine! Who would have ever imagined in 1941 that someday computers would come in the size of today’s laptop? The Cerebral cortex (neo cortex to be more specific) is the latest addition (phylogenetically) to multicellular organism and but is the most demanding part of the body. Just contemplate this,
Percent of total body weight that the brain represents = 2% (avg.)
Percent of body’s oxygen consumed by the brain = 25%
Percent of body’s glucose burned up by the brain = 70% Average
Percent of body’s nutrients consumed by the brain = 25%
Percentage of the brain’s total volume constituted by the cerebral cortex = 25%
Percentage of the brain’s neurons housed by the cerebral cortex = 80-85%
Percentage of cerebral oxygen consumption by white matter = 6%
Percentage of cerebral oxygen consumption by gray matter = 94%
If we suppose that all the organs were independent entities feeding on the body’s nutritional stock, the brain especially the cerebral cortex will come highest in the pecking order. So much so for the late comer! Going by this pace, it’s not so difficult to surmise Cerebral intention of being self-centred and to write-off other ‘members’ of the living body!
The dominance of neurons in the animal world did not last from time immemorial. There has been a time when another cell was the domineering one. This would be evident on a careful examination of the timeline of the evolution of life. In the Jurassic period of (200 to 145 million years ago) Mesozoic Era, the size of animals reached its peak. Nature always follows a rationale (and hence we have science to explain it!) and therefore it needs to be questioned as to why animals attained such colossal sizes? Going by Darwin’s theory of evolution, these colossal animals did not just appear on earth one fine day rather, they evolved to that form to adapt to the environmental and ecological conditions then. The obvious answer is survivability. Just as neurons have ensured us survivability today (survivability of the fittest), mere massive size then ensured survivability of the animals. It was a time of raw power and thick hide, and muscles just ensured that. Therefore, that was the era of dominance by muscle tissue and many colossal sized animals called dinosaurs appeared on the face of earth. These colossal sized animals reigned over 160 million years on earth. Just as the mighty third Reich didn’t last forever, so did the dominance of muscle tissue end sometime in the end of the Cretaceous (about 65 million years ago) when the Dinosaurs became extinct. It’s said that meteorite impact on earth had widespread environmental consequences on the planet leading to mass extinction. It’s plausible that the impact was so devastating that it must have led to conditions similar to a nuclear winter. So when plants, the foundation of almost every food chain began dying out and food became scarce the colossal animals requiring more food intake were the first to fall. It can thus be put this way that the muscle tissue became a victim of its own success. This should remind us that the time of neuronal dominance will also end someday. The pace at which mankind is polluting the nature and playing God will one day sound a death knell for itself. Probably we needn’t even wait for another meteorite impact. The Dinosaurs and hence the dominance of muscle tissue lasted on earth for over 160 million years, we Humans have just registered a mere 50, 000 years in comparision!
We all have identified ourselves so much with our own Cerebral cortex and the component neurons that we fail to realize that the cerebral cortex is just 25 % of the brain volume which in turn is only 2 % of the Human body weight. It’s amazing that this small piece of tissue has been the causative factor for many if not all aspects of human life and also of this world (not planet of course). It is this tiny piece of tissue is what makes us creatures as Homo sapiens, the ‘wise man’. What we call as science, technology, literature, philosophy, politics, economics, society, state, nation, etc. did not trickle down from the pancreas or gall bladder but are all outcomes of that tiny bunch of neurons inside our skull. It has been a long time since the first cell appeared on earth and thence, life has diversified in so many ways that it’s difficult to imagine where it all began. Somewhere in the evolutional history of life, came the neurons too and they have etched a spectacular impact in the ecology and biosphere. No single cell has changed the face of earth as much as did this one did - the disappearance of many animal and plant species, the reduction in green cover of the planet, the spread of urban jungle, the radiation poisoning of environment, the mass murder of fellow beings on the lines of religion or ethnicity, pollution of thousands of rivers. As I stand staring at the Golgi stained neuron under the microscope, I wish we are just made of liver and lungs!