Human Spiritual Structure: The Physical Body
Notes in progress © 1998-2002 Alan McAllister  

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The Nervous System

The human nervous system has two main components, the central and autonomic nervous systems. The central nervous system is comprised of the brain, twelve pairs of cranial nerves, the spinal cord, and thirty-one pairs of spinal nerves. These have both afferent (sensory) and efferent (motor) fibers, for messages going into and out from the spinal cord and brain. [SB]

The autonomic nervous system includes the sympathetic and parasympathetic nervous systems. The former branches out from a trunk line of sympathetic ganglia along the spine. The later branches off from the Vagus nerve(10th cranial) which lies in front of the spine. The functions controlled by the autonomic nervous system are not normally under conscious control, but this may be changed by practices such as pranayama, or bio-feedback training. The former works in through the ability of either main nervous system to control the href="body.htm#breath"> breath. [SB]

The main nerve plexi are associated with the chakras. These are the Sacral, at the base of the spine, the Hypogastric, behind the genitals, the Solar, between the naval and the sternum, the Cardiac, around the heart, and the Pharyngeal, at the base of the throat. The upper three have both sympathetic and parasympathetic nerve feeds, while the lower two have mainly sympathetic nerves and only filaments from the vagus. A Nasociliary plexus associated with the Ajna chakra is also mentioned. [SB]

The sympathetic nervous system is activated in the fight or flight reactions. It prepares the body for action, and is stimulated by emergencies and various excitements. It tends to be involved in the expression of strong emotions, even positive ones. This system is centralized in the brain.[HB]

The parasympathetic nervous system is activated in the conservation withdrawal reactions. This system reverses the actions of the sympathetic system, slowing the body down and returning to a more normal level of operation. This system is distributed, having nerve clusters near the various organs.[HB]

These two systems are mutually exclusive, when one is up the other is down. They involve different nerve circuits and different neurotransmitters (norepinephrine and acetylcholine respectively).[HB]

Among other functions, the autonomic nervous system communicates directly with the immune system[EI].

There is a separate system for pain. Both special sensors and a priority set of nerves to convey the signals to the brain. [HB]

The Indryas or Organs of the Body

In yogic terms there are ten indryas, or organs. The five sense organs, or jnanendriyas (organs of knowledge) are the eyes, ears, nose, tongue, and skin. The jnanendriyasare comprised of the sense organs together with the nerves, nerve fluid, and the appropriate seat in the brain. There are also five organs of action (karmendrya), which are the mouth, the arms, the legs, the anus and the genitals.

The Immune System

The immune system is a complex system of cells and molecules distributed throughout the body, which has the function of identifying "foreign" substances and molecules and then rallying the bodies defenses against them. It has a similar range of actions to the nervous system, being able to send and receive signals, which can be excitatory or inhibitory, and to remember and learn. Like the nervous system it has sensors for monitoring external and internal conditions and can respond to these by regulating body functions. It includes the the thymus gland, the spleen, the bone marrow, and the lymph nodes. [HB]

There are two types of immunity, natural and acquired. Natural, or innate" immunity is a function of all cells by which they react to tissue damage via inflammatory processes which allow other cells or molecules to come to their aid, in particular in order to fight and contain viruses. Acquired immunity is embodied by the lymphocytes which are produced in the bone marrow. They are modified either in the thymus (T-cells) or in the bone marrow (B-cells) (fetal processes are somewhat different). These cells patrol the blood stream looking for trouble in the form of hostile cells, viruses, or other substances (collectively antigens), which they then attack and destroy. There are a wide variety of T-cells with different roles in these processes. There are also macrophages (which consume antigens) and natural killer cells which attack tumor and virus infected cells. [HB]

There are millions of types of lymphocytes in the infant some of which match antigens which are a natural part of the body, and are therefore turned off, the rest evolve to handle external antigens. These have receptors that match to the various viruses, bacteria, toxins, or other products of disease. Once matched that type clones itself very rapidly, produces antibodies which combine with and deactivate the antigen, and other types of cells (e.g. macrophages) are marshaled. In a healthy system there are all sorts of potentially troublesome antigens, viruses, mutated cancerous cells, toxins, etc. but the immune system handles them before they become dangerous. It is the weakening, or imbalance of the immune system that leads to disease. As well as diseases where the immune system breaks down, or fails to contain a threat, there are also "autoimmune" diseases where it becomes over active, reacting to harmless antigens (allergies) or even attacking parts of the body itself. Lupus is an extreme example of these autoimmune diseases, in which the immune system reacts to the bodies own DNA as an antigen. It appears to be affected by psychological stress. [HB]

While stress of various sorts, both physical and mental is a clear factor in disease of various types (see below) it appears that it is the response to the stress as much as the stress itself that is important.

Immune and Nervous System Interaction

The immune system is affected by psychological stress. It is usually generally depressed by the loss of a loved one, a sudden loss of job, natural disasters, or other events that cause a sudden, and major change in the external environment, especially those that affect the social network, or ones sense of personal well being. It is through the connections between the nervous and immune systems that the mind can directly affect the health of the body. All of the components of the immune system are well supplied with nerves. Removal of these nerves severely impedes the immune response[EI}. The lymphocytes have receptors to a wide range of hormones, neurotransmitters, and other nerve chemicals that may serve to control various aspects of lymphocyte function.

Hormones that are released in response to stress dampen the activity of the immune cells.

The most common chemical messengers in both the brain and the immune system are densest in the areas the regulate emotion.[EI]

There is evidence that left-handed persons are more likely to suffer from immune system problems (mostly of the thymus and bowels), as well as from migraine headaches. There is other evidence that the proper functioning of the left hemisphere of the brain is related to full immune system function. This may be due to the impact of "hostile" emotions associated with the right hemisphere. It is known that "hostile" rather than angry people are most likely to suffer the heart attacks and strokes of the type A personality. [HB]

The immune system also appears to depend on the hypothalamus, with evidence for two way communication. Immune responses are correlated with increased activity in the hypothalamus, while a damaged hypothalamus eliminates a known immune response. Activation also significant changes in the levels of the pituitary neurotransmitter norepinephrine, possibly due to control from the hypothalamus. That the hypothalamus is involved in the emotions suggests a pathway for the linkage of emotional states and the strength of the immune system. [HB]

The various neurohormones that are released in response to physical or psychological stress that activate the sympathetic nervous system, are known to depress the immune system (e.g. corticosteroids). While natural killer cells are apparently suppressed by the endorphins released in reaction to pain, as well as mild stresses and loneliness. Those who cope "poorly" with stress are generally found to have depressed immune systems. Experiments with cancer in rats find that stress induced changes in the immune system correlate with susceptibility to tumor growth. When the stress was escapable the immune system was toughest, while inescapable stress significantly depressed it. In people high expectations (externally motivated) coupled with low performance increases susceptibility to manifesting mononucleosis when infected with Epstein-Barr virus. In people infected with herpes, their depression about having the disease increased the likelihood of an outbreak (a form of resistance).

Stresses related to a "need for power" also appear to depress the immune system, probably due to increased activity of the sympathetic nervous system. There is good evidence that the way people deal with anger affects their susceptibility to cancer and their ability to survive it. Suppression of emotions, especially anger (fear) is highly correlated with cancer and mortality. Those who fight are more likely to survive, possibly because they were more in touch with the stress and willing to express it.[HB]

There is somewhat less evidence that psychological factors can boost the immune system, in part due to the possible differences between fighting existing disease, and resisting its appearance to begin with. Studies have shown that hypnotized subjects could boost their immune systems, and that relaxation programs for elderly also had a positive affect. Humor is also associated with increased immune functions.

The Circulatory System

The phenomenon of blushing illustrates the connection between emotions and the heart. Blushing is a signal of increased blood pressure. It can occur "internally" as well, i.e. without the outward signs of reddening. Studies show that talking to someone raises the blood pressure slightly, but talking to someone who is of "higher" status raises the blood pressure much more. [The significant factor is probably not the absolute status, but the perceived feeling of inferiority, which makes one nervous and takes them off center.] [HB]

People with hypertension (high blood pressure) can learn to control it through monitors that show them how it goes up and down as they speak. Speaking about emotionally charged topics can also lead to increases in blood pressure. In the classic Type A people it is now felt that ongoing anger, or hostility, which cuts one off from other people, is the key factor. The hurriedness, or multitasking are not necessarily correlated with heart troubles. The most endangered are those who are often and easily angry, but hold it in. These folks tend to be very judgmental, particularly in thinking oneself superior to others. Self-involvement is a recognized factor in heart disease and hypertension. Self-centered and hostile people have higher blood pressure and tend to react more strongly to stress or challenge. The high levels of adrenaline and high blood pressure, both damage the arteries. It appears that it is selfishness behind business, rather than business itself that is dangerous. Business in the service of others is not a problem, as long as the motive is really to do service. [HB]

There are also heart attacks which are due to a sudden upset, excitement, or shock. These may happen even to otherwise healthy people and show an affect similar to that of the immune system. It is generally due to a rapid, ineffectual, beating of the heart. This is thought to be the result of emergency arousal, but uncertainty about the best course of action, fight or flight. Thus both the sympathetic and the parasympathetic nervous systems may become activated, and the heart is torn between conflicting messages, the heart speeds up, but its muscle tone is relaxed. Studies with beta-blockers, and other drugs, indicate that the controlling messages come from the brain, in particular the frontal lobes (stress interpretation and decision making) and the hypothalamus (which sends out fear messages). These are cases where "the brain cannot make up its mind", due to external or internal ambiguity of a charged situation.[HB]

The heart is also a gland in that it produces the hormone atrial natriuretic factor (ANF) when the blood pressure rises. This hormone affects kidney function, salt levels, and also the pituitary . [GLE]

Social Connectedness and Illness

There is a great deal of evidence that people who are connected to the world around them, through family, friends, pets, or plants, are healthier and less likely to die or to commit suicide. Strong social networks provide a stability that can help to contract the effects of sudden environmental changes, e.g. the death of loved ones, loss of a job, etc. If the level of uncertainty, and the stress that goes with it becomes too high, or too sustained, then a person is more likely to become ill or to die. This need for social connection is due in part to evolutionary factors. Man's upright gate forced changes in the body including a heavier pelvis with a smaller opening. Therefore a human baby's brain is only 25% grown when it is born (compared to a baboon's 70%). This means most of the brain forms after birth, resulting in a long period of helplessness in which the infant needs to attach to its mother. Bonding ensues. Because the mother cannot provide enough food, while also taking care of one or more infants, changes in sexuality lead to the more or less permanent presence of a male who can provide food for a family. I.e. the human family and social nature is in part an evolutionary necessity. [HB]

The advantages of social bonding show up in the statistical differences between men and women, in and out of marriage. This is due to the more active role that women take in forming and maintaining close relationships. In marriage men benefit from this activity by their spouses. Social support and interaction are found to benefit laboring mothers, and aged nursing home residents. The later show increases in anabolic hormones, which boost the body's overall health.[HB]

There is also the famous study of students watching Mother Teresa serving the poor (tapah). Even those who consciously stated they disliked her had their immune systems boosted for at least an hour. The lack of connectedness shows up in depression of the immune system , leading to illness and cancer, as well as the coronary system, leading to heart disease and heart attacks. [HB]

Breathing and Body Functions

The breath ( prana) is a level of energy that is very important as a link between the mind and the body. Breathing is an interface between the central and autonomic nervous systems, as either one can be used to work the lungs. Through the practices of pranayama it is possible to learn to control the autonomic functions. As we control our breathing (i.e. the lungs) we also can control the heart. [SB]

In yoga the bodily functions are associated with breathing through either the right or the left nostril. This shifts both the tempo of the metabolism and the mind. When the right side dominates the metabolism increases, while the mind is more focused externally. In particular this is the mode for digestion, elimination and physcial exercise. When the left side dominates the metabolism is calmer and the mind can more easily focus and turn inwards. This is also the recommended state for performing asanas. Many actions are traditionally recommended for one state or the other. In order to open the desired side pressing under the armpit of the opposite side for several minutes will effect the change.

When napping after a meal, or first going to bed it is best to lay on the left side. For general sleep the right side is better. Laying on one side will naturally open up the nostril on the other (upper) side. [SB]

There are three phases of breathing, diaphragmatic, thoracic, and clavicular. Chest breathing is most common, but diaphragmatic is most efficient, especially when the body is upright. This is because there is more blood flowing through the bottom third of the lungs, due to gravity, and so using the diaphram (pushing out the stomach muscles), and using the lower lungs, leads to the most efficient transfer of gases to and from the blood. This means that the heart can slow down.[SB]

The natural alternation of the breath from one nostril to the other, on the order of two to three hours per side, is also necessary. In the yogic literature it is reported that if one side should dominate for as long has 24 hours illness is likely to occur. The balance is necessary to overall health. [SB]

The shape of the nasal passages is apparently quite important. Significant changes can affect a persons personality and moods. This illustrates the key role played by the breath in the mental and emotional bodies as well as the physical. The rhythm and regularity of breathing is also very powerful and is related to emotion. The yogis have found that certain emotions tend to generate certain breathing patterns. Conversely, those breathing patterns will bring up the same emotions. This is part of the power of rebrithing. [SB]

Body Cleansing

The body normally releases toxins and waste in the urine and the feces, in the exhaled air (mostly carbon dioxide), and in the perspiration. At times they may also be expelled in saliva and mucus, and in extreme cases through sores in the mouth or on the skin. There are various practices, including fasting, internal washes, and breathing exercises which facilitate these clearing processes. This is part of the general process of seeing health as the result of a good internal ecology rather than just a good external ecology. Both are important.

The mucus membranes in the lungs and nasal passages have a secondary function of expelling waste from the body. When other channels are overwhelmed or plugged up, then these membranes will increase their secretions, giving rise to a cold or other illness. It is therefore important to bath these and help keep them clean. [SB]

Muscle Types

There are broadly two types of muscle fibers, Type I and Type II. The first burns sugars and is meant for fast, short-term, action. This is called anaerobic exercise and creates lactate. The second burns fats and is meant for long-term , smoother action. It is called aerobic exercise and burns lactate creating water and carbondioxide. There is a third energy pathway that kick starts the fight or flight activity of the Type I fibers. This is based on burning phosphagens and lasts typically for 30 seconds or so. [GLE]

Working and Learning with the Body.

See also these articles notes.

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Page Created, February, 1998.
Last updated February, 2000.
© Alan McAllister

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