Our brain and central nervous system
by Luke Kristopher Davis
As you follow the evolutionary history of life on earth you will see that organisms grow in their complexity and efficiency. This complexity is a consequence of minute alterations to DNA which result in complex organs, this alteration is a result of natural selection. Natural selection is a process which sieves out genes that are no longer useful, are faulty or another gene for a similar function is a much more adapted gene for that environment. Fast forward this process for a couple of billions of years then as a consequence of natural selection, a vast array of complex organisms will have formed.
Homo-sapiens, as with sperm whales ( Physeter macrocephalus) and the scorpion (Hadogenes troglodytes), are products of evolution. We have developed (as with our ancestor the chimpanzee) a complex nervous system and brain. Our complex nervous system has helped us in sensing our environment and equally in processing and acting upon it. Homo-sapiens in particular have a complex brain, we are able to communicate with other humans in enormous detail and we are capable of complex abstract thought. As you can see around you, the human brain is capable of understanding nature and its governing dynamics, enabling technology and a very complicated social structure.
In this article we will explore the mechanisms that underpin our interactions with the world (central nervous system) and our brilliant cognitive machine.
The Central Nervous System
The central nervous system (CNS) is the body’s control center. It is analogous to the pilot’s cabin and the electronic system of radar and radio to a plane. CNS co-ordinates all the humans actions, both mechanical and chemical (working with hormones) and is made up of the brain and spinal cord. The millions of nerves that perpetuate throughout the body carry electronic impulses from certain tissues, through the spinal cord up to the brain and this happens in the opposite direction too.
“The brain is a wonderful organ; it starts working the moment you get up in the morning and does not stop until you get into the office.”
– Robert Frost
The brain is the organ that controls most of the body’s activities. It is responsible for advance cognition, conscious movement and unconscious activities e.g. controlling the food movement through the intestines. The brain is the only organ able to act ‘intelligently’ which is action based on past experience stored as information, present events and future plans. It is made of millions of neurons arranged into sensory, association and motor areas. The sensory areas receive information from all body parts and the association areas analyse the impulses and make decisions. The motor areas send messages (orders) to muscles or glands. The impulses are carried by the fibers of 43 pairs of nerves – 12 pairs of cranial nerves serving the head and 31 pairs of spinal nerves.
The parts of the brain:
The Cerebrum: The largest, most highly developed area, with many deep folds (which is a sign of complex neuron and lobe structure… advanced cognition). It is located above the cerebellum and the thalamus. The cerebrum is made out of two cerebral hemispheres, joined by a band of nerve fibers (corpus callosum) and its outer layer is called the cerebral cortex. This contains all the most important sensory, association and motor areas. It controls most physical activities (yes… even sex) and is the center for mental activities such as decision-making, speech, learning, memory hippocampus lobe and imagination.
The Cerebellum: The area of the brain which co-ordinates muscle movement and balance, these two are under the overall control of the cerebrum.
The midbrain: An area joining the Diencephalon, which is a collective term used for the thalamus and hypothalamus, to the pons. It carries impulses towards the thalamus, and out from the cerebrum towards the spinal cord.
Pons or Pons Varolii: A junction of nerve fibers which forms a link between the parts of the brain and the spinal cord (via the medulla).
Medulla or medulla oblongta: The area which controls the “fine tuning” of many unconscious actions (under the overall control of the hypothalamus). Different parts of the medulla control different actions.
Thalamus: This is the basic traffic center of the brain, it directs the oncoming nerve impulse traffic to different parts of the cerebrum. It also directs some outgoing impulses.
Hypothalamus: The master controller of most inner body functions. It controls the autonomic nervous system (nerve cells causing unconscious action) and the action of the pituitary gland. This gland is made out of two anterior and posterior lobes which produce hormones for the body, these hormones are mainly of the tropic variety, these hormones stimulate the action of other glands in the body. This part of the brain is vital for keeping our internal systems in order.
The lobes and parts of the cerebrum
The different hemispheres of the cerebrum focus on different cognition. The left is more analytically orientated, focusing on language and computation. The right is more creative and more focused on visual imagination.
The spinal cord
The spinal cord is a long string of nervous tissue running down from the brain stem inside the vertebral column. Nervous messages from all parts of the body travel through it, some are carried away from the brain and some enter towards it. Others might be dealt with in the cord.
As you can see in the diagram spinal nerves branch from the cord through gaps in vertebrae. There are over 31 pairs of these spinal nerves. Nervous fibers branch from these nerves and so on around different organs and limbs. Each spinal nerve is made out of a sensory root and a motor root, the former sends signals into the brain, the latter sends signals to muscles or glands.
In the spinal cord exists neuroglia which are stiffened cells which support and protect the nerve cells of the central nervous system. Some produce a white, fatty substance called myelin. This coats the long fibers found in connective areas of the brain and the outer layer of the spinal cord, and leads to these areas being called white matter. Grey matter on the other hand consists of cell bodies and short fibers which do not produce myelin.
On a molecular level, the governing dynamics of both the brain and spinal cord are greatly caused by the structure and mechanisms of a nerve cell or neuron.
The neuron is made up of a cell body, nerve fibers, dendrites and sometimes axons. The cell body is the part of the neuron containing its nucleus and most of its cytoplasm. The cell bodies of all association, some sensory and some motor neurons lie in the brain and spinal cord. Those of the other sensory neurons are found in masses called ganglia.
Nerve fibers are extensions of the sytoplasm of the cellbody and carry vital nervous impulses to other neurons, muscles or parts of the brain. Most of the lond nerve fibers which run out round the body are accompanied by neuroglial cells which produces myelin around each fiber. Dendrites are the fibers carrying impulses in towards the cell body, axons are the long fibers which carry signals away from the neuron in query.
There are three different types of neurons: sensory, motor and association. Sensory neurons carry information to other neurons, they are detectors and are vital for the bio-mechanical system, they fire signals when stimulated. Association neurons are special linking neurons present in vast quantities in the brain and spinal cord. They pick up information and interpret the sensory information and pass this to the right motor neuron. Motor neurons are responsible for action, they receive information and when stimulated cause muscle contraction or the chemical production of hormones in glands.
Between nerve endings is a synapse which is a small gap between the dendrite and axon of two neurons. A neuro transmitting chemical is produced from the axon to stimulate the continuation of the electrical signal.
The human body as you can see is beautifully complex yet astonishingly efficient. This is why human consciousness seems so ethereal and quite incomprehensible,with time however neuro-scientists, physicists and biologists may come to model the complex process of consciousness. We have also gained an insight into nature, how nature builds intelligence. We may as humans learn from this and when building artificial intelligence use the phenomena witnessed in the human brain as an example.
A question is raised however, is this the only way nature can produce biological intelligence and complexity? Is there another way which an alien life form may take?
Time will tell.
Thanks goes to ADAM for images