If we look at the human body from an engineering point of view, we notice that it has many types of inputs and outputs. The traditional five senses process stimuli from outside the body, or exogenous signals. However, because the body is a very complex structure, there are also endogenous or internal signals that can be perceived by the senses. Many of these stimuli cannot be detected immediately, but only after they have had an effect on the body. Sometimes the effect of these stimuli is on the brain, and if this causes decreased mental function it may prevent us from becoming aware that we are affected.
The very act of breathing, which we have to do several times per minute, brings air into our lungs and whatever else is in the air. Our nose hairs filter out insects and some dust, but gases like carbon monoxide, vapors, smoke, pollens, bacteria, viruses, and small dust particles are carried into the lungs. The body has many self-cleansing mechanisms to keep the lungs clean, but constant exposure to air pollutants eventually take their toll on the lungs or other organs of the body. The tar and chemicals carried in the smoke of cigarettes has been linked to many types of respiratory disorders and nicotine has an addictive effect on the brain. Carbon monoxide produced by gasoline motors or charcoal fires in enclosed places interferes with the oxygen-carrying function of the blood and is responsible for many deaths each year. Paint solvents and gasoline fumes can damage the liver. Gases like nitrous oxide and vapors like ether affect the nervous system and are used as anesthetics.
We have to eat and drink to sustain our life, but what we ingest can carry not only nutrients, but also substances that can adversely affect our health and mental processes. There are regions in the United States where there is a great prevalence of kidney stones that are associated with the hardness of the water. The "goiter belt" is another region where the soil has a deficiency of iodine that would result in thyroid gland problems were it not for iodized salt. Grain tainted with ergot fungus, which has an LSD component, has been theorized to have caused hallucinations responsible for the witch hunts in Salem, Massachusetts.
We cook foods to make them more digestible and to kill harmful microorganisms and parasites. However, cooking may decrease the nutritional value of the food and charring during grilling may create nitrosamines that have been associated with some cancers. Our mass markets require the preservation of food by the use of food additives. Many of these preservatives were discovered by analyzing foods, such as cheese, which don't readily spoil. Other food additives are only used to improve appearance, e.g., artificial colors. Not all additives are harmful, but some people prefer to buy "natural" or "organic" products because they do not want to eat residual pesticides used in agriculture. Some "natural" and "organic" products may be quite harmful. Opium, coca leaves, marijuana, and tobacco are all natural products with addictive or mind-altering properties. This does not mean that they may not have legitimate medical uses. Opium has been the source of morphine, which is a powerful pain killer.
Caffeine, which occurs naturally in coffee, tea, and chocolate, is a nervous system stimulant and also a diuretic. Large amounts of caffeine can cause tremors or shaking. Caffeine can be addictive for some people even in small amounts. It is not by coincidence that soft drink manufacturers use caffeine as an additive. If you drink more than one cup of coffee, tea, chocolate, or cola drink per day you may be addicted to caffeine. This can be easily verified by abstaining from caffeine-containing foods or drinks for a couple of days. Restlessness, sinus pressure, or headaches are common withdrawal symptoms.
Medicines and drugs may be administered orally, by injection, inhalation, etc. The purpose of medicines is to help the organism return to a healthy state. However, sometimes medicines are prescribed to maintain a "normal" state. Antibiotics fall into the first category. Once an infection has been eliminated, the medication can be stopped. Diabetes is in the second category. It is necessary to take insulin all your life in order to live normally. With the large number of drugs available, it is not surprising to find that some of them interact or interfere with each other. Some women on birth control pills have become pregnant while taking some types of antibiotics. Also, grapefruit has been found to elevate levels of some medicines to toxic levels.
"Recreational" or illegal drugs such as heroin, cocaine, and LSD are mind-altering drugs that affect the brain adversely, sometimes permanently. Certain non-prescription medicines, such as cough suppressant syrups with dextromethorphan, act on the brain and can dull thinking and creative abilities. "Ritualistic drugs", such as peyote, have hallucinogenic properties and are used in certain religious ceremonies. Alcohol is the most frequently abused mind-dulling drug. It acts as a brain intoxicant that reduces reaction times and impairs the motor functions of the body. Drugs used in psychiatry also modify the way in which the brain works. When used to treat depression or other debilitating mental conditions these drugs actually help to restore the normal functions of the brain, but generally not without side effects.
The skin acts as a protective barrier for the body, but it is not impervious. Many substances pass through the skin and can affect various organs of the body. When the skin is exposed to harsh chemicals, such as chlorine bleach or detergents, there may be just a local irritation or chemical burn. Organic solvents such as gasoline, mineral spirits, and dry cleaning fluids can be absorbed through the skin and reach toxic levels in the body. The liver is the organ most frequently damaged as it tries to detoxify these substances.
Electromagnetic radiation can be good and it can be bad for the body. It depends on the type of the radiation and the duration of the exposure. Infrared radiation, which is low-frequency radiation, is felt as heat. Sitting by a fireplace or a pot-bellied stove on a cold winter night can feel comforting without any harmful effects. Excessive doses of infrared radiation can result in burns. Normal skin produces Vitamin D when exposed to sunlight for brief periods of time. When exposed for long periods of time, the skin reddens and becomes painful to the touch. Repeated exposure to sunlight stimulates the skin to produce a protective dark pigment called melanin. Chronic exposure to sunlight eventually breaks down the cellular structure of the skin and can result in wrinkling, cancerous melanomas, or other skin disorders.
The amount of light to which the body and eyes are exposed may affect the central nervous system. Seasonal Affective Disorder (SAD) is a form of depression that includes feelings of sadness, tiredness and cravings for carbohydrates. It is believed to be related to the decreased sunlight in winter and the release of melatonin. Melatonin is usually produced by the pineal gland at night and induces sleep. Besides sunlight, the body may also be exposed to moonlight, which is sunlight reflected off the moon. The light of the moon is weak, but it enabled early humans to have some nighttime activities before the invention of fire and artificial lighting. The word "lunatic" is derived from the Latin for "moon". At one time it was believed that the influence of the moon triggered mental disorders.
The use of artificial lighting has introduced some problems that did not exist before its invention. Some people are sensitive and can get headaches from the flickering of fluorescent lights. The flickering is particularly noticeable in the peripheral vision. Flashing images from television or strobe lights can also cause harmful effects to the nervous system and can trigger seizures. A Japanese television cartoon program that used flashing pictures to simulate an explosion sent several hundred children to the hospital with various neurological symptoms.
High-energy radiation such as ultraviolet light, X-rays, or Gamma rays can destroy cells. X-rays and Gamma rays have greater penetration than ultraviolet light and are used medically for diagnostic imaging and to burn tumors. Ultraviolet lights, also called "black" lights, are used in hospitals and grocery stores to kill bacteria, but sometimes they are misused for entertainment in bars or other dark places because ultraviolet light makes some substances fluoresce.
Cosmic rays, which are high-energy particles, normally do not penetrate the earth's atmosphere. However, astronauts have reported seeing flashes of light that have been attributed to the effects of cosmic rays either on the eyes or the visual cortex of the brain.
Our bodies respond to sounds in fairly mechanical ways. Sudden noises can cause a person to jump away from the noise, or turn the head in the direction of the noise. Soothing, rhythmic noises such as the sound of the sea, a gurgling brook, or the beating heart in a mother's breast are well known for their calming effects. Buzzing sounds close to the ears cause us to wave the hands by our ears as if to repel insects. Certain high-pitched noises such as scratching fingernails on a blackboard or the noise of a pencil on paper can "make your skin crawl", which is an erection of the hairs on the skin. Loud repeated noises can reduce the sensitivity of the ears and eventually cause hardness of hearing or even deafness. Boilermakers that used noisy riveting equipment were particularly prone to deafness as an occupational hazard. In the era of high-fidelity sound equipment with powerful amplifiers, many young people are losing their hearing by listening to music at very loud levels.
Bacteria and viruses come into the body principally through the eyes, the mouth, the skin, and the nose. Some bacteria actually have a beneficial effect. The "normal flora" that are found in the mouth release substances that prevent more harmful bacteria from getting established. Other bacteria aid in digestion or produce vitamins and nutrients that the body can use. Bread, yogurt, beer, wine, vinegar, and many types of cheeses are produced by using specific types of non-harmful yeasts, bacteria, or fungi.
Disease-causing bacteria release toxins that interfere with normal body processes. Viruses, which are much smaller than bacteria, work against the body by re-directing the synthesis of normal cell components into replication of the virus. The body tries to fend off bacteria and viruses by generating chemical antibodies and by increasing body temperature. Fever creates a more hostile environment for bacteria but can result in delirium and other forms of mental changes. Some diseases like rabies or polio attack directly the nervous system. Learn more about Bacteria and Viruses.
Insect bites and stings are unpleasant inputs to the human body. Insect stings inject toxins into the body that may elicit allergic reactions accompanied by nausea, pain, and swelling. The bite of the black widow spider is sometimes fatal. Some blood-sucking insects inject saliva at the point of the bite. Insect saliva may cause swelling and itching, but it may also carry bacteria or parasites. Bubonic plague, the so-called "black plague" of the middle ages, which is a bacterial disease, is transmitted by flea bites.
Parasites come into the body through many mechanisms. Inhale the dust of a soiled bed linen, and you may get pinworms. Take a dip in a lake or river and get schistosomiasis. Get bitten by a mosquito and get malaria or sleeping sickness. Hug your mother and get follicle mites. Eat uncooked pork and get trichinosis. Eat food contaminated with fecal matter and you may get roundworms. Roundworms generally inhabit the intestine, but because of their complex life cycle, sometimes they end up in other parts of the body, including the brain. Learn about Hygiene.
We live immersed in the magnetic field of the earth. The human body is generally not affected and cannot detect this magnetic field. Homing pigeons, however, have been shown to use the earth's magnetic field as one means for returning home. In principle, however, the electrical activity of the nervous system could be affected by strong magnetic fields, and recent experiments suggest that magnetic fields may help to reduce certain kinds of pain.
Our sense of equilibrium in the gravitational field of the earth is provided by the semicircular canals in the ear. These canals are lined with filaments that are stimulated by calcium carbonate crystals suspended in a fluid. The rotation of the moon around the earth every 27 1/3 days creates tidal forces that affect many living organisms, but is not known to have a significant effect on humans. Some fish are known to spawn in the beach at high tide when the moon is full. The human menstruation cycle of approximately 28 days may be a legacy of our ancestral origins in the sea. See The Geologic and Biological Timeline of the Earth.
We can sense changes in air pressure as pain or discomfort in our ears, sinuses or bones. The nerves surrounding the body cavities that contain enclosed pockets of air detect volume changes caused by external air pressure.
Endogenic inputs come from within the body to the brain. When we start exercising, carbon dioxide builds up in the body. This buildup acts as an endogenic signal for the heart and the lungs to work harder. When the level of glucose in the blood drops, we get hungry. Hunger, thirst, pain, fatigue, kinesthesia are all inputs to the brain from the body itself.
Some physiological cycles like menstruation may trigger feelings of fatigue, irritability, and depression as the hormone levels change. Exercise has been credited with stimulating the body to generate endorphins that create a feeling of well being. Emotions such as fear release adrenaline into the bloodstream, which triggers many systemic reactions. Several studies have found that what you think can affect your health. Constant worry can create stress that lowers the body's ability to fight diseases, whereas positive thoughts and laughter can actually improve your health.
Verbal communication might have been included under sounds. However, the effect of verbal input on the mind is so different from that of the wind blowing or other noises encountered in nature that it is considered separately. Imagine that your boss calls you to his office and says something neutral like: "In two weeks we are having a meeting to discuss the progress of our new project". Your reaction may be one of anticipation or apathy. Not much is required from you except your participation. However, if the boss says something negative like: "You made several mistakes in your last report and I am very dissatisfied with your work". You may become angry or scared, your heart may start racing and you may want to justify what you did. Words have the power to make you laugh or the power to make you cry because they are not only sounds. Words have meanings that get to the root of your emotions.
Since ancient times words have had mystical power because they could represent objects, feelings, curses, etc. The word "abracadabra" was supposed to have magical powers against disease or disaster, and sometimes it was carried in an amulet. Prayers were more than just words; they provided a way of communicating with the deities.
Much can be deduced about the state of mind of a speaker from their speech. The tone of the voice can convey authority, fear, doubt, and many other different emotions.
If analyzed carefully, this category could also be grouped under other senses. However, there are some inputs that connect to the fears or desires deep within our brain and establish a special kind of non-verbal communication. The snarl of a dog, a cat rubbing against our legs, a gentle massage, or the wink of an eye are all special kinds of communication. These are more than just simple sounds or visual or tactile inputs. They are meaningful messages for the brain.Next Outputs from the Body