Issue 78 / November - December 2010
It's Me Peter! Your Nervous System - 2
When you hear the words ‚Äúnervous system,‚ÄĚ what comes to mind is a cluster of cells called neurons. But this is a great mass of cells, and we should always remember that we are referring to the most complex matter in all of creation.
(continued from the previous issue)
Using the distinct groves and folds on the hemispheres as a guideline, a map drawn on the cortex identifies focal points, where the various senses are concentrated, and activities in particular regions. Each of these different colored schematic centers has a specific name and performs specific functions. For example, the region above the neck at the back of the head (occipital lobe) is the field of sight; the sections that coincide with the temporal region is the field of hearing; immediately in front of this, on the left, is (generally) the field of speech; in the forehead region (frontal lobe), on the anterior wall of the middle canal is the initial center of planning of movement; on the top section of the front region is the field of complex movement; immediately behind here, in the middle-side region, is the field of simple movement; the area behind this, next to the hearing field and extending upwards, is defined as the touch receptive field. However, these areas are not confined, but rather spread out, and have a very complex connection network. The duty of the adjoining areas of these regions is to display and decipher the meaning of the signals received from the nerves. As the received signals regenerate past experiences and memories, the object or event sending the signal is recognized. To perform voluntary complex movements, the plan of movement must initially be defined in the mind and then the combination of this plan is conveyed through my nerve fibers to the movement regions. As complicated activities in humans, such as talking, and activities that involve the sensory integration mechanisms are miracles in themselves, it is quite astonishing that certain people claim that humans evolved from apes, later learning how to speak. The spinal cord (medulla spinalis) that extends from the skull in the form of a long cord, is the central nervous system sending signals to the body regions under the neck. The grey matter of the brain is located on the surface, while the white matter lies beneath the cortex; however with the spine, the butterfly shaped grey matter is inside, and the white matter on the surface covers the grey matter. In this central nervous system, all of the sensual messages that are received from the entire peripheral system, in particular from your skin and muscle, are immediately connected with the synapses or connections of the movement cells, and thus a spinal reflex is produced. As a section of the connecting cells (synapses) responds with a reflex, the other section transmits the signal to me to determine the appropriate voluntary response. For instance, if you tread on a nail, as the nail goes into the foot, a signal is transmitted by the sensor fibers to the spine, and to avoid a loss of time, the spine immediately signals the movement nerves before me, and a command is transmitted to your muscle you to raise your foot. And after your foot is saved by instant reflex, you begin to perform the other conscious activities, for example; you avoid putting weight on the foot, and bandage the wound if it is bleeding.
31 pairs of nerves (right and left) emerge from the spinal cord; 12 pairs from the brain area lay beneath the skull. These are all nerves that emerge from the central nervous system, and are distributed to various organs of the peripheral nervous system. All of the head nerves that emerge from the skull, with the exception of the tenth nerve, called the vagus nerve, control activities related to movement and senses in the head and neck region. Each of the 31 nerves exit from a space in the side of the vertebrae, and each of these nerves has two roots, an afferent nerve (sensual nerve), and an efferent nerve (movement nerve). These roots join immediately outside the spinal cord, and form the cords that carry the sensual and movement nerve fibers. These nerve cords are distributed in a plan and system that is specific for each organ. For example, the receptor sensor cells that sense a needle pricking your finger transmits this signal to the spinal cord through the receptor cell of the arm. The responsive reflex of pulling the hand away, a reflex from the spinal cord, is sent to the arm and hand muscles, and you pull your hand away. This is an example of a simple reflex. The movement nerve cells of the peripheral nervous system are divided into two, the somatic nervous system, which is distributed to the skeletal muscles, and the autonomic nervous system, which is distributed to the inner organs. Whilst the majority of the activities of the somatic systems occur voluntarily at the conscious level, the activity of autonomic systems is mainly involuntarily, or below the level of consciousness. The autonomic nervous system controls the smooth muscles of the heart, glands, blood vessels, respiration, digestion, urination and reproduction systems without our even realizing it. Dear Peter! Could you manage to do all this if you were in control? Your self control can only intervene until you place food in your mouth. Then the digestive secretions, the stomach and bowel activity, and the excretion of waste are all conducted automatically, totally beyond your control. Your breathing continues while you sleep, your kidneys never cease to function, your heart never rests, and your liver never relaxes while you sleep; your pancreas continues to produce insulin. All of your internal organs and blood vessels continue to function with the smooth muscles whenever necessary. And all this activity is conducted without you even being aware of it. If you tried to do all this, you would become exhausted within five minutes, lose interest and become unable to cope.
The nerve cords of the autonomic nervous system are divided into two, the sympathetic and the parasympathetic. These two systems have been created in such a way that they respond in opposition to one another, and every organ is provided with a stem from both. Therefore, no organ of the body is left uncontrolled. Whilst one signals and encourages the organ to function quicker and generate more outcomes, the other acts to the contrary, sending signals that encourage the organ to slow down. In which case, with these two contrasting signals, the organ protects its optimal functioning tempo according to the situation and conditions. The sympathetic system generally responds in cases of stress and shock, preparing the body for the effects of such situations. For example, an increase in your blood pressure, blood-sugar level, and perspiration, the dilation of your pupils, and an increase in the flow of blood in your muscles all occur from the effect of the sympathetic fibers. The parasympathetic system sends adverse signals, such as reducing blood pressure and so on, so that the organs return to their neutral state and continue their normal functions.
From the very beginning I have described many of my sections and signals, but I have not yet told you about my key to life, my nerve cells, and how my nerve cells function. 30 billion cells, known as neurons, are the actual units that function in every part of my system. A neuron has a cell body and emerging filaments like tree branches. The single thicker filament like the tree trunk is called the axon, and the thinner filaments that emerge in larger quantities like tree branches are called dentrites. The nerve signals advance from the axon to the dentrite in the form of an electrical pulse. In the space between the connection point (synapses) of a nerve cell axon and the other cells, the dentrite, a chemical substance, called the neurotransmitter, is released. When these substances, in the form of neuropeptides, amino acids, acetylcholines, and monomines, reach the wall of the opposite cells, it an electrical pulse is immediately ignited in the dendrite. Just like a row dominos, falling down one after the other, or football fans performing the Mexican wave, a wave-like effect is generated and these electrical messages are fired with great speed from one end of the cell to the other, advancing in the form of tiny electrical pulses to be transmitted to neighboring cells. While a cell at rest has a potential of 70m V, the action potential of up to +30 - +40m V can transmit all types of information. Every cell can transmit up to 1,000 signals per second.
While you still do not recognize the true value of what you call the memory, which records hundreds of experiences every day, various theories are presented regarding how this bank which stores information in your brain actually functions. But we all know that the answer to this question lies within the millions of neurons that constitute me. Just as all of the senses, thoughts and actions occur from electrical and chemical signals that are transmitted from one cell to another they are presumably recorded in the same way, that is, with electrical and chemical signals.
It is difficult to define a precise center for the boundaries of the memories in me; memory could be interconnected with all of my regions. The storing of certain memories, some voices, visions, smells, or dreams, or the sense of resentment, anger or joy, is all carried out in different forms. You could not even begin to imagine the greatness of the memory storage! I have two types of memory, one short and one-long term. In my short term memory, I can store up to between seven and nine different things at any one time. Nothing remains in my short-term memory for more than a few minutes. Everything that you remember after this is stored in my long-term memory. In my long-term memory things can remain for days, months or even years. Everything you know and learn is stored in your long-term memory. By the time you are eight years old, the information in your memory is enough to fill one million pages. However, this is a mere drop in the ocean; the long-term memory is so vast that it can never become full. Even when you reach a hundred, I will have the capacity to store new information, so never assume that you are overloading a child‚Äôs mind and never deprive them of education‚Ä¶Some presumptuous people say; ‚ÄúNever force a child to memorize at a young age, it will affect the brain.‚ÄĚ Do not believe them! The learning of foreign languages, the Qur‚Äôan and religious education is recorded in my memory by electric pulses and this is so much easier and healthier in the early stages of life. In fact, such activities at a young age can even strengthen the memory. The event called ‚Äėrecollection‚Äô is the repeat of the electric pulse codes that are recorded at the actual time of an event. Occasionally you try to remember a person‚Äôs name, and although the name is on the tip of your tongue, you just cannot remember. You struggle and eventually give up. Then suddenly, two days later the name comes to your mind. You are quite puzzled and of course pleased that you have remembered, but have you ever wondered how this happens? As you try to remember, you control each of my nerve cells individually, because you are not sure where you placed the files that bear this information. But you are unable to find which section of the millions of cells bears the information. As you have not used this information often, or because you did not consider it to be important, you did not register it in a particular place. But you would never forget your father‚Äôs name, as it is important to you and use it often, so the file is in front of you constantly. Well, you get frustrated at not being able to remember and stop searching; however, what you call the subconscious is in fact a much more mysterious mechanism. It begins to search without you being aware of it. Then to your surprise it produces the file two days later. The subconscious is a very mysterious place, it affects everything about you. Only the most sincere feelings are recorded in the subconscious; no veil, no hypocrisy, only actual thoughts are recorded. And also events that deeply affect you, the sad or bad memories you experience, and of course sins‚Ä¶The subconscious is what causes the sense of guilt or an inferiority complex; this is reflected in much of your behavior. But problems like guilt or an inferiority complex are something we can change; it all depends on you. If you are a person who has self-control, you perform good, favorable deeds, and are continuously patient; thus you can eventually renew the contaminated sections of your subconscious so that it will not upset you anymore. Indeed, this is the reason why, of all the creatures on earth, only humans were blessed with the sense of remorse and faith. If you suppress feelings of guilt and sin in the subconscious, the autonomic system affects the organs without you even realizing it; the thalamus, hypothalamus, or the pituitary gland (hypophsis), which are small in size, but bear a great responsibility; eventually this disturbs the balance of the whole body and you become ill. Although this may not be an organic complaint at first, due to psychosomatic symptoms which are caused by suppressing your subconscious, over time this will affect the functions of one of your organs and you become ill. Of course the exact opposite is also possible, with inspiration, pleasant thoughts and good actions the positive signals transmitted to the affected organ may possibly be the means to recovery.
Dear Peter! I have so many more facts and mysterious functions to describe to you, but unfortunately the pages here are not enough. Well, I suppose I must stop somewhere. I really wanted to talk to you about a number of different things, like dreams, mental illnesses such as Parkinson‚Äôs, Alzheimer‚Äôs, strokes, sleep, hypnosis, and the damage caused by drugs. However, each of these subjects is so vast, and many of them have already been explained in previous issues, so for now I will leave it to others to describe these subjects to you, and say my last words‚Ä¶
Dear Peter!... While your hand is writing and reading these words, or explaining what you have read to your friends, or learning all this information and passing it through the filter of thought, you are constantly using my nerves and my systems. There is not a single moment where I am not informed of events that occur in your body. Who knows just how much of the mysteries in me you will use in order to rise to the peak of accomplishment with the blessings that have been bestowed upon you by the Creator. Even the greatest computers made by human beings are mere toys compared to me. Nevertheless, the knowledge of engineers and craftsmen which design, plan, and place every piece into these computers with total accuracy is only possible because of me. Presumably you are not denying those who designed, constructed, and made the computer operate, are you? In which case you should thank God, the One who created me, an organ whose capacity exceeds that of thousands of computers, with His eternal power and wisdom; always remember to use me in good, blessed, and honest actions!‚Ä¶May God protect you!...
Irfan Yilmaz is a professor of biology at Dokuz Eylul University, Izmir.