BOUNDARY

23

SUBSYSTEMS THAT PROCESS BOTH MATTER-ENERGY AND INFORMATION

THE BOUNDARY

A living system’s boundary i s a region at its perimeter that separates the system from its environment. I t surrounds and protects vulnerable components, acts as a b a r r i e r to free movement of m a t t e r , energy, and information in and out of the system, and filters i n p u t s and o u t p u t s by allowing some but not others t o pass. Because t h e boundaries of living systems resist penetration, more work is commonly required t o cross t h e boundary than t o move on either side of it. At least some of the boundary components for processing m a t t e r and energy are different, in systems at all eight levels, from boundary components for processing information. Boundaries make it possible for the concentration of some sorts of matter, energy, and information t o be greater inside a system and others to be greater in the environment. This allows systems t o maintain their low-entropy state, accumulate useful forms of matter, energy, and information inside t h e boundary, return products and wastes to the environment, and keep out harmful or undesirable inputs. BOUNDARY PROCESSES AT THE LEVEL OF THE CELL

Chemical and biophysical research has revealed many details about the structure of cellular boundaries. The cell’s outer membrane, t h e plasma membrane, is the primary boundary component of all cells in addition t o being a component i n several other subsystems. Plant cells have firm cell walls outside the membrane and some bacteria, including the bacilli that cause

Behavioral Science,Volume 37,1992

tuberculosis, have tough capsules. These are additional boundary components. Both the plasma membrane and the cell wall are components of other subsystems as well a s of t h e boundary. The cells of organisms a r e s u r rounded by tissue fluids or, in bone and cartilage, by a matrix t h a t contains calcium. Neurons i n t h e brain a r e surrounded by neural supporting and protective cells, t h e glia, which a r e additional boundary components. Myelin sheathes composed of fatty materials, proteins, and water also surround and insulate axons of neurons of the peripheral nervous system and of white p a r t s of t h e central nervous system. Other neurons i n t h e gray m a t t e r and some of t h e white a r e essentially bare. The plasma membrane. The plasma membranes of cells a r e boundary components of both the matter-energy and information boundaries, since processes of both take place in much the same way. The molecular structure of the plasma membrane is similar in all cells although the specific molecules differ from one cell type to another. The basic framework is a double layer of phospholipid molecules separated by a space. Proteins of various sorts are the other major membrane component. Lipids are a class of compounds that includes a great variety of fats, oils, and waxes. Phospholipids are one sort of lipid molecules. The phospholipids differ in molecular composition but they all have a hydrophilic (soluble in water) head group made up of a phosphate linked t o a residue that can be either choline, ethanolamine, serine or inositol.

24

MILLER AND MILLER

T h e h e a d g r o u p is a t t a c h e d t o two hydrophobic (not soluble in water) tails, each of which is a fatty acid chain. I n w a t e r , phospholipids s p o n t a n eously arrange themselves into a bilayer with the longest axis of the molecules roughly perpendicular t o t h e plane of the bilayer. The hydrophilic ends face water on both sides of the bilayer. The oily hydrophobic tails are in the middle of the bilayer, excluding water from it. Phospholipid molecules in water form closed spherical vesicles which separate the fluid inside from the fluid outside ( B r e t s c h e r , 1985, pg. 101). S u c h a phospholipid bilayer is a liquid. Cell membranes are bilayers of this sort. They enclose the cell's contents in a m e c h a n i c a l l y s t r o n g b u t soft a n d flexible envelope. Because of i t s oily interior, t h i s envelope i s essentially impermeable t o molecules like amino acids, s u g a r s , p r o t e i n s , a n d nucleic acids, all of which are soluble in water a n d insoluble in oil. Ions also have difficulty in crossing the membrane. In addition t o the phospholipids, cholesterol and glycolipids are also present in the membrane. Because the membrane is liquid, most of its molecular constituents can diffuse freely from side t o side within their own monolayer. Phospholipid molecules can change places with each other about once every microsecond ( B r e t s c h e r , 1985, p. 102). T h e phospholipids a r e s t r u c t u r a l components. The specific functions of t h e m e m b r a n e a r e c a r r i e d o u t by proteins, the molecular composition of which i s d e s c r i b e d above i n t h e discussion of the reproducer subsystem. The proteins of t h e cell membrane can be roughly classified into two kinds according to t h e i r s h a p e (Bretscher, 1985, pp. 102-103). Helical proteins are rodlike, coiled into a tight spiral called a n a l p h a h e l i x . M a n y of t h e s e a r e receptors for large extracellular molecules. T h e y h a v e h y d r o p h i l i c peptides o n t h e surface of t h e mem-

Behavioral Science,Volume 37,1992

b r a n e , which a r e a t t a c h e d t o a hydrophobic alpha helix t h a t spans the membrane, and a hydrophilic tail t h a t a n c h o r s it i n t h e cytoplasm. O t h e r helical proteins serve as markings on the cell surface, like those t h a t allow cells of t h e i m m u n e s y s t e m t o distinguish between cells of a n organism's own body and invading bacteria or other potentially harmful proteins. The second kind of membrane proteins are globular. An important part of t h e i r s t r u c t u r e l i e s w i t h i n t h e bilayer. Many globular proteins form channels through which certain kinds of molecules can pass into the cell. Enzymes a r e p r o t e i n s t h a t a c t a s catalysts in cellular chemical reactions. They can recognize a specific sort of molecule; b i n d t o i t ; c h a n g e it by splitting it, adding other molecules t o it, or changing the pattern of bonds in it; and then release i t , leaving t h e enzyme unchanged. Other proteins are s t r u c t u r a l elements t h a t a t t a c h to protein molecules like themselves to form sheets, tubules, or fibers. T h e cilia a n d flagellae t h a t propel many free-living cells through t h e i r liquid environment and that are parts of some sorts of organism sensory cells are also com-posed of protein fibers. Matter-energy boundary. The s t r u c t u r e of t h e p l a s m a m e m b r a n e suits it for forming a protective barrier between the inside of the cell and its e n v i r o n m e n t since it i s d e n s e r a n d tougher t h a n its usual liquid s u r roun di ngs. As a living system, a cell must ingest t h e m a t t e r - e n e r g y i t n e e d s for i t s processes a n d e x t r u d e products a n d w a s t e s . Cell m e m b r a n e f i l t e r i n g p r o c e s s e s d e t e r m i n e w h a t s o r t s of molecules can cross t h e boundary into or out of the cell. Filtering processes a r e of two kinds: passive, which requires no expenditure of energy by the cell; a n d active, which does r e q u i r e e n e r g y e x p e n d i t u r e . Diffusion i s a passive process that occurs when there

BOUNDARY are differing osmotic pressures on the two sides of t h e plasma membrane. Water, for example, diffuses into and out of cells in the direction of the concentration gradient. That is, if there is a higher concentration of dissolved substances on one side of the membrane than the other, water flows toward the higher concentration, tending t o even the pressure. Dissolved oxygen and carbon dioxide also enter cells in this way. Small molecules t h a t do not ionize strongly in solution diffuse into cells in the liquid in which they are dissolved. Substances t h a t a r e soluble in lipids also c a n diffuse t h r o u g h p l a s m a membranes. Water-soluble substances cannot pass through plasma membranes by diffusion. Molecular size is also important. Very large molecules cannot diffuse through cell membranes. These include some m a t e r i a l s t h a t a r e essential in cell processes as well as some products a n d w a s t e s . Such molecules, if they are to enter or leave t h e cell, m u s t u s e energy t o open channels through which they can be ingested or extruded. The processes t h a t open c h a n n e l s a r e boundary subsystem processes. The series of chemical reactions t h a t take place to move t h e molecules into t h e cell a r e ingestor or input transducer processes. If a molecule of t h i s s o r t is t o be ingested by a cell, it must encounter an appropriate receptor on t h e plasma membrane. Each type of cell has on its membrane a different assortment of proteins, some of which are receptors for specific molecules t h a t c a n be ingested by that type of cell. Receptors are large protein molecules that span the membrane from its outer surface to t h e cytoplasm. They function by binding the molecule, which induces an allosteric change in the receptor t h a t opens a channel through which t h e molecule can be ingested. Information boundary. Bacteria and prokaryotes process little information

Behavioral Science, Volume 37,1992

25

but all eukaryotic cells, whether freeliving or aggregated, receive signals from sources in the environment. The markers t h a t carry these signals a r e molecular configurations and specific energy flows, such as light waves. Free-living eukaryotes, which can swim from place to place, a d a p t t o environmental change by avoiding or approaching certain stimuli. All freeliving cells are not sensitive to the same s o r t s of energies b u t some s o r t s t o which one or more cell types have been observed to respond are light, warming and cooling, gravity, extremes of acidity or alkalinity, and pressure. Some of the receptors for these energies have been identified. Euglena gracilis and Chlamydomonas, have eyespots that contain light-sensitive pigments. Many types of cells without eyespots also respond to light. Chlamydomonas, which orients itself against gravity, also has receptors for t h a t sort of energy (Bean, 1977). Paramecia, which respond to several energies, b u t not t o light, have been shown to have receptors for warmth and cold. Consequently, the cells c a n respond to t h e r a t e of t e m p e r a t u r e change by swimming toward or away from t h e i n p u t (Inoue & Nakoaka, 1990). Cold receptors are located at the a n t e r i o r of t h e cell. Receptors for warmth are distributed over the rest of the cell. Cells aggregated into the tissues of organisms receive signals from t h e organism’s environment, from other components of the organism, or both. Molecules of hormones a n d growth factors are markers for information for cells of all types. These circulate in the organism’s blood stream, which is the vascular component of the channel and net subsystem. Neurons, muscle cells, a n d gland cells-except t h e cells of endocrine glands-also receive signals on molecules of neurotransmitters that carry the nerve impulse across the gaps (synapses) between neurons and the neurons or other cells to which they

26

MILLERAND MILLER

transmit information. For sensory cells, m a r k e r s include such energies as pressure, light, sound, or gravity or the molecules that carry odors or tastes. Boundary information processes of cells d e p e n d upon t h e e l e c t r i c a l characteristics of the plasma membrane. When a cell is “resting”-that is, when it i s n o t stimulated-the outside of i t s membrane is electrically positive with relation to the inside. Ordinarily t h e potential difference, called the resting p o t e n t i a l , i s b e t w e e n 10 a n d 100 millivolts. Essentially all vertebrate cells maintain an internally negative membrane potential of -60 millivolts (Catterall, 1984, p. 653). This difference i n potential r e s u l t s from a difference in ion concentration between the inside a n d outside of the cell. The fluid within t h e cell contains a high concentration of potassium ions while t h e e x t r a c e l l u l a r fluid is h i g h e r i n sodium a n d calcium ions. Since t h e membrane i s passively permeable t o these ions, they leak in and out of the cell. The potential difference is maintained by a n active process t h a t uses the cell’s energy to “pump” ions across t h e membrane a g a i n s t t h e gradient. “ P u m p s ” a r e protein molecules t h a t open ion c h a n n e l s t h r o u g h t h e membrane. There are two types of ion channels in t h e p l a s m a m e m b r a n e s of n e u r o n s , voltage-gated and ligand-gated (Stevens, 1984, p. 1346). In voltage-gated channels, t h e probability of a g a t e being opened i s determined by the potential difference between the inside and the outside of the membrane. Pumps are of t h a t sort. Ligand-gated channels are opened when a transmitter substance binds to a receptor on the membrane, bringing about a conformational change in the receptor molecule-an allosteric protein-that opens the channel. This m a y b e in t h e r e c e p t o r itself o r in another molecule. Unlike the similar ingestor process, in which the molecule that binds to the receptor is taken into

Behavioral Science,Volume 37,1992

the cell, the transmitter does not enter the cell. If the transmitter is excitatory, it depolarizes the neuron. This results in the flow of sodium and calcium into the cell and the flow of potassium out, transmitting the signal to input transducer components of the neuron. T h e process of information t r a n s mission by hormones and growth factors also involves the binding of informationbearing molecules to receptors on cell m e m b r a n e s a n d t h e o p e n i n g of ion channels. The boundary process is similar when the information is carried on an energic marker. The receptors for warmth o n the plasma membranes of Paramecia increase m e m b r a n e conductance for calcium i o n s by o p e n i n g calcium channels; the receptors for cooling open channels for potassium ions (Inoue & Nakaoka, 1990, p. 107). The boundary processes of sensory cells of organisms a r e also similar in many ways. Electrical signals in t h e hair cells that respond to the pressure of sound waves originate from the flow of ionic c u r r e n t s across t h e m e m b r a n e (Hudspeth, 1985, p. 748). The molecules that form the ion channels in these cells have not been identified but they allow positively charged ions including pot a s s i u m , sodium, calcium a n d some others t o flow into the cell. More is known about t h e structure and processes of rods, the visual cells t h a t function in dim light. These are long, thin cells with an outer segment, the rod outer segment, t h a t is outside the plasma membrane. It is composed of s e v e r a l h u n d r e d t o a few t h o u s a n d f l a t t e n e d , s t a c k e d disc m e m b r a n e s , which a r e enclosed by an o u t e r membrane and which contain the visual pigment, rhodopsin (O’Brien, 1982, p. 962).

Rhodopsin i s a l a r g e protein t h a t s p a n s t h e d i s k m e m b r a n e from i t s surface t o the disk interior. It has two components, 1l-cis-retinal, which is derived from vitamin A; a n d opsin, a

BOUNDARY protein that acts as an enzyme. When a photon of light is absorbed by the 11-cis retinal, the rhodopsin is bleached. The 11-cis retinal is transformed into transretinal and the enzymatic action of opsin is triggered. This sets in motion a cascade of biochemical reactions that carries the signal from the membrane of the rod outer segment t o the plasma membrane of the lower segment of the cell. The effect of these reactions is to close sodium channels in the membrane, hyperpolarizing them and causing a receptor potential to be propagated along the membrane.

27

clusters of cells are components, the plasma membranes of those cells. These can function as one organ because they are coordinated by information flows over the channel and net subsystem of the organism. If however, a structure is a component of only one subsystem, as the urinary bladder is a component of only the extruder, the entire structure is within the boundary of that subsystem or organ, along with any other components of that subsystem. It is convenient t o refer t o discrete structures like the heart or bladder as “organ components”. The vertebrate pancreas, for example, includes comBOUNDARY PROCESSES AT THE LEVEL OF ponents of t w o functional organs. THE ORGAN Clusters of acinar cells produce digestive We define organs in terms of process enzymes that are components of the rather than structure. Each of the converter subsystem. Scattered patches essential subsystem processes of of cells, the islets of Langerhans, secrete organisms, together with the structures insulin, a hormone that controls the t h a t carry it out, is a n organ. The amount of sugar stored in the body. boundaries of organs are, therefore, not These are decider subsystem coponents. necessarily continuous in space o r The liver of vertebrates is composed of uniform in structure, and are rarely cell o r tissue components for several congruent with discrete structures of the matter-energy and information procesorganism such as the heart, lungs, and sing subsystems. kidneys t h a t are called “organs” by Ma t t e r - e ne rgy b o u n d a r ies of o rga n anatomists and in common usage. components. With few exceptions, organ Instead, most organs of higher organisms components are not able to filter matterare composed of cells and tissues within energy that reaches their boundaries, the boundaries of more than one such either from other structures t o which structure. The producer, for example, is they are connected by a valve or duct, or composed of cells and tissues in many from the circulating blood of the different parts of the organism. organism. The filtering process is largely Matter-energy boundary. The matter- downwardly dispersed t o the separate energy boundary of a structural organ is cells, which allow certain molecules t o a wall, capsule, or layer of tissue that cross their membranes and exclude surrounds it and separates it from other others. parts of the organism. It is a protective The walls of the stomach and instructure t h a t acts a s a barrier t o testinal tract of higher animals are harmful matter and energy from the composed of several layers of tissues, outside. Such boundaries are penetrated including epithelium, smooth muscle by openings like valves, ducts, and the tissue, and tough connective tissue. regions where the blood and lymph Matter-energy that is input at the mouth vessels of the organism connect with is moved by muscles of the wall through those of the organ. successive components, each of which The boundaries of organs are made up breaks it down further. Indigestible of the outer layer of cells of their materials are extruded. component tissues or, if single cells or The heart is surrounded and protected

Behavioral Science,Volume 37,1992

28

MILLER AND MILLER

by the pericardium, a double-walled sac particularly after meals o r exercise. If containing a small a m o u n t of serous t h e b r a i n w e r e exposed t o s u c h fluid, that provides a smooth surface for f l u c t u a t i o n s , t h e r e s u l t m i g h t b e t h e heart’s movements. If a n a c u t e uncontrolled nervous activity, because change in heart volume occurs, as when some hormones and amino acids serve a n u n u s u a l l y l a r g e a m o u n t of blood as neurotransmitters and potassium ion flows into the ventricle, the pericardium influences the threshold for the firing of limits diastolic expansion of the right nerve cells. To prevent this, the brain ventricle (Detweiler, 1973, pp.3-27). must be isolated from transient changes This protects t h e left ventricle from in t h e composition of t h e blood” overload and the pulmonary circulation (Goldstein & Betz, 1986, p. 74). The necessary constancy is provided from congestion. I t also p ro t e c t s against blood flowing backward through by the specialized structure of the brain the mitral or tricuspid valves when the capillaries and by a “metabolic barrier”. Capillaries are the small blood vessels ventricle fills under high pressure. H u m a n s k i n , a complex s t r u c t u r e t h a t ramify through all tissues of the t h a t includes components of several organism, forming a “capillary bed” organism subsystems in addition to the w h e r e f i l t r a t i o n a n d diffusion of b o u n d a r y , h a s a n o u t e r l a y e r , t h e molecules from t h e blood i n t o t h e s t r a t u m corneum-a horny l a y e r of intercellular fluid take place. Capillary epithelial tissue that covers the entire walls in all but a few parts of the body organism except a t a r e a s where t h e are freely permeable to substances in mouth, nostrils, sweat glands, excretory the blood. I n addition, t h e capillary organs a n d sense organs open t o t h e walls of s o m e o r g a n s h a v e g a p s or e n v i r o n m e n t . T h i s o u t e r l a y e r i s channels running through them. This is continually renewed as cells of lower not true of brain capillaries. Except in layers die, come to the surface, and are the pituitary gland, t h e pineal gland, s h e d . It p r o t e c t s t h e t i s s u e l a y e r s and parts of the hypothalamus, the cells beneath it, and prevents entry of many that compose capillary walls are joined forms of harmful matter or energy and by continuous “tight junctions”. That is, loss of tissue fluids. t h e o u t e r l a y e r of t h e p l a s m a The central nervous system of higher membranes of adjoining cells merge so animals h a s three protective layers of t h a t t h e cells a r e physically j o i n e d tissue (the meninges) and cerebrospinal (Goldstein & Betz, 1986, p. 74). As a fluids t h a t absorb shock a n d prevent result, molecules t h a t easily penetrate damage t o the delicate structures they capillary walls in other parts of the body surround. A further barrier, the blood- cannot e n t e r t h e brain. When horseb r a i n b a r r i e r , a c t s as a f i l t e r t h a t radish peroxidase was injected into the prevents the passage of many sorts of blood s t r e a m , i t could n o t p a s s t h e molecules through t h e walls of brain capillary walls. When it was injected dicapillaries (Goldstein & Betz, 1986). rectly into one of the cerebral ventricles, T h e n e u r o n s of t h e b r a i n a r e which a r e fluid-filled cavities in t h e especially sensitive to fluctuations in brain, it flowed into t h e extracellular t h e composition of t h e extracellular spaces of t h e brain. I t was, however, fluids, from which they take up matter- prevented by the tightly joined cells of energy, as Goldstein and Betz explain in t h e capillary walls from leaving t h e brain. the following passage: “Elsewhere in t h e body, t h e extraT h e blood-brain barrier is not comcellular concentrations of hormones, pletely impassible. Molecules soluble in amino acids and ions such a s potassium lipids readily get through the lipid cell undergo frequent small fluctuations, walls a s they do in cell walls in other

Behavioral Science, Volume 37,1992

BOUNDARY parts of the body. Nicotine, ethanol (the alcohol in alcoholic drinks), and heroin get into the brain that way. Watersoluble molecules are excluded. These include necessary inputs such as glucose, the brain’s source of energy, and some essential amino acids. These are transported across capillary walls, probably through protein channels that have so far not been identified (Goldstein & Betz, 1985, p. 78). The distribution of such channels on the capillary walls is not symmetrical, so that certain molecules can pass easily out of the brain but far less readily in the other direction. An enzyme called sodium-potassium ATPase forms the basis of a pump that transports sodium out of the cell wall of the capillary into the brain and potassium out of the brain into cells of the capillary wall, from which it is returned to the blood stream. Much more of this enzyme is present on the side toward the brain. The other important part of the bloodbrain barrier bars substances from entering the brain by converting themby metabolic processes-into a chemical form that is incapable of passing through the capillary wall. L-dopa, an amino acid precursor of the neurotransmitters dopamine and norepinephrine, readily passes into the cells of the capillary wall where it is modified by enzymes into a form that cannot reach the brain. Another barrier, this one between the choroid plexus and the cerebrospinal fluid, is also a filter for molecular input and output (Spector & Johanson, 1989). The choroid plexus consists of several small patches of tissue in the ventricles of the brain, which are cavities in the brain filled with cerebrospinal fluid. This fluid circulates through the spinal cord and brain. Nutrients in it pass into the intercellular fluids in the brain. The cells of the choroid plexus secrete the cerebrospinal fluid which provides a chemically stable environment for the brain, buoys up the brain so that it is protected from injuries that

Behavioral Science,Volume 37,1992

29

could result from moving the head, and contains molecules needed in the brain’s metabolism. The barrier between the choroid plexus and the cerebrospinal fluid functions in many ways like the blood-brain barrier. Under a microscope, the choroid plexus looks like a network of densely branched fronds. Each of these consists of capillaries whose walls consist of a single layer of epithelial cells joined by tight junctions that impede passage of even small water-soluble molecules between the blood and the cerebrospinal fluid. The choroid plexus transfers different nutrients into the brain than reach it from the blood. These are substances that are needed in small amounts over extended periods, such as some vitamins. It also transfers waste products of the brain’s metabolism from the cerebrospinal fluid to the blood. These processes involve active transport that pumps molecules across the epithelial membrane. Cells of the epithelium that lines the upper intestinal tract perform boundaryfiltering processes in much the same way. This epithelium is a single layer of cells, bound together by tight junctions (Bretscher, 1985, p. 104). Its function is t o allow useful materials-and no others-to pass from the intestine into the blood stream of the organism and remove materials that are not useful from the blood. The two sides of the membrane allow materials t o be transported in one direction only. Protein pumps on the side of the epithelium near the inside of the intestine, for example, bring sodium into the epithelial cells. Proteins on the “blood” side pump the sodium from the cell into the organism’s blood stream. Information boundary. Structurally, the information boundaries of organs are similar t o those of the matter-energy boundary. That is, they consist of the information boundaries of whatever whole organ components the subsystem includes as well as the information

30

MILLERAND MILLER

boundaries of the single cells and the cells of tissues that are components. I n f o r m a t i o n boundaries of organ components. These boundaries are at the places where blood from the vascular component of the organism channel-andnet subsystem, which carries hormonal information, flows into and out of the intrinsic blood circulation of the organ component. They are also a t places where components of the organism’s neural-channel-and-net subsystem synapse with neurons of the channel and net of the organ component. Organ components receive neural information over channels of the sympathetic and parasympathetic divisions of the organism’s autonomic nervous system. Information flows out of organ components over neurons of the organism’s peripheral nervous system, from sensory cells in the components’ walls. These are parts of the organism channel and net subsystem t h a t report the internal state of organs to the central nervous system. In autonomic pathways leading t o organ components from the central nervous system, there are two peripheral neurons, unlike the skeletal nervous system which has only one. Autonomic neurons in the spinal cord synapse with preganglionic neurons that synapse with postganglionic neurons. The cell bodies of these postganglionic cells are in ganglia, either at some distance from the organs that are innervated (sympathetic division) or within the walls of the innervated organ (parasympathetic). We regard the synapses between preganglionic and postganglionic neurons as the boundary of the organ component, even though those of the sympathetic division are not within the organ. The information boundaries of organ components do not act as barriers, protective structures, o r filters for information. Hormonal information is filtered at the boundaries of the cells that make up the component, a downwardly dispersed process.

Behavioral Science, Volume 37,1992

BOUNDARY PROCESSES AT THE LEVEL OF THE ORGANISM The boundaries of organisms have specialized components for matterenergy and information boundary processes. In all animal species, the skin or external membrane is the major boundary component. Except where sense organs and passages for matter-energy open t o the environment, the skin is continuous over the entire body. The boundary is also continuous over the sense organs, which have specialized tissue layers between them and the environment. Matter-energy boundary. The boundary of animal organisms consists of whatever surface structure delimits the organism from its environment.These are continuous over the whole body except at openings for the mouth and other orifices, and at places where the sense organs open t o the surface. In higher organisms it is the skin-with its reinforcements of fur, hair, spines, horns o r antlers. I t is interesting t o note, however, that the mucous membrane that lines the mouth and digestive tube is continuous with the skin. Organisms have the form of a torus (any solid that rings a hole as a doughnut does). Although in one sense ingested matterenergy is “in” the body when it is in the digestive tube, in another it is not in the body until it has been filtered by cells of the intestinal wall into the blood stream. Some forms of matter-energy never get inside in this sense. Ingested matterenergy is, however, universally regarded as inside the body when it is in the digestive tube. The skin of human beings and of other higher organisms is a remarkable organ component t h a t is far from a passive barrier between the organism and its environment. It carries out many adjustment processes that protect bodily components from being damaged by impinging matter and energy of various kinds. Blood flow in the skin increases or decreases with temperature change to

BOUNDARY dissipate heat or hold it in the body. Since the outer layer of skin cells is continuously replaced, it maintains its integrity against the inevitable wear and tear of daily life. It acts as the first line of defense against many kinds of invading bacteria by marshalling the white cells of the blood to attack and kill them. Through tanning, human skin protects t o some extent against ultraviolet radiation, although it cannot prevent long-term damage. It is also an important component of the information boundary. The shape o r colors of boundary components blends many animals into their environment or make defenseless, little creatures look bigger, fiercer, o r less delicious than they are. Changes in color t h a t match animals t o their backgrounds allow some animals t o hide effectively. Skunks, which are soft, slow-moving, and not well-equipped to fight, are not t h e only animals t h a t protect themselves with unpleasant odors, but they do it with notable effect. The spines of a porcupine-another small, slow animal-assure that predators will avoid it. Sense organs are also protected from damage by boundary components. The iris and lens of the eye filter ultraviolet rays from the sun and prevent damage to the sensitive retina at the back of the eye. Eyes are set into bony sockets and provided with lids that can close to shut out very bright light and protect against other harmful sorts of energy and matter. Protection is given to the sen-sitive cells of the ear by the bones of the skull, by the external ear, and by the ear drums that cover the canal and block the entrance of harmful forms of matter. No anatomical provision i s made for protecting against damage from loud noises. Covering the ears with hands or paws is possible for some species. Artifacts can be important aids to this subsystem. Nests, burrows, buildings, human clothing, eyeglasses, and weapons

Behavioral Science, Volume 37,1992

31

of various kinds all reinforce organism boundaries. Information boundary. Except for the eyes, which can close, the areas and structures of the boundaries of higher organisms that are especially adapted to receive information input have no structural defense against input of unpleasant o r excessive information. Organisms defend against unwanted information input by using adjustment processes like turning away, covering their ears, or using adjustment processes like those that human subjects used in studies of information input overload (Miller,1978).

BOUNDARY PROCESSES AT THE LEVEL OF THE GROUP Matter-energy boundary. A group’s matter-energy boundary is the outer extent of the region occupied by the group when it is assembled. When a meeting is over or family members go to their separate jobs o r schools, t h e individual members go outside this boundary. It re-forms when some or all members come together again. If, however, a part of the group is working or meeting separately outside t h e group’s territory, the matter-energy boundary is dispersed. Each subgroup has a matter-energy boundary at its outer limits, in much the same way as t h e boundaries of organs surround spatially separated organ components. At levels above the organism, we use the convention that people and other organisms are matter-energy, although we recognize t h a t they may also be markers carrying information. The matter-energy boundary of the living system at any particular time is not ordinarily i n exactly t h e same location a s t h e group’s territorial borders-the space inside a family’s apartment walls, within the outer limits of its yard, the limits of the workspace assigned to a work group in a building or factory. The territory is usually larger

32

MILLER AND MILLER

than the space occupied at any given time. While a group’s territory is often fairly regular in shape and slow to change, the boundaries of the living systems vary in shape as components change their positions in space. Family members move about their home. Members of social groups form a variety of patterns as they play games, listen to lectures, or meet for meals. The territory defended by a football team is the a r e a behind t h e scrimmage line, all the way to the goal post in the end zone behind them. The boundary of the living system consists of the bodies of t h e players. When two professional teams face one another waiting for the kick-off, their lines are formidable boundaries. During play, defensive players intercept forward passes and tackle opponents that carry the ball into their territory while they try to move forward and claim a larger part of the field. The dimensions of a team’s territory can change very rapidly. An important part of matter-energy boundary function i n some s o r t s of groups is keeping nonmembers of the group from entering the group’s t e r ritory. A committee sends a member to tell such invaders t h a t a confidential meeting is going on. Social groups and informal clubs usually admit new members from time to time. Before a new member is admitted, a boundary filtering process-determining whether they a r e suitable and acceptable-takes place. A bridge club needs four players for each table. Adding a replacement for a member who leaves the group may be taken very seriously. For this process, all the remaining members of the group are components of its boundary. Boundary processes are frequently laterally dispersed to all members of the group as they are when an infantry squad spreads out to protect the perimeter of the territory it is holding. The subgroups or individuals t h a t maintain boundary artifacts a r e also living boundary components. Animals, particularly dogs,

Behavioral Science, Volume 37,1992

are often components of this subsystem. Other living components of the boundary subsystem are the individuals or subgroups that protect group members and make sure that people, animals, and various forms of matter-energy are kept on the proper side of the boundary or border, either inside or outside. A babysitter makes sure the toddler stays in t h e yard. Members of a work group around an excavation and send sightseers on their way. Artifacts are of great importance as nonliving boundary components i n groups and at higher levels. Bullet-proof glass i n t h e windows of a limousine protects a group of gangsters or a chief of state and his entourage. An electrified fence keeps a family’s cows in a field and holds rustlers out. A t e n t protects a group of campers from rain and prowling bears. A group’s matter-energy boundary may also be upwardly dispersed t o a n organization. This is true when families depend upon a city police force o r a security company for protection or when a work group’s room a n d tools a r e guarded by other components of t h e organization to which the work group belongs. I t can also be upwardly dispersed to the society, which occurs when national guard troops help to fight a n approaching forest fire. I n f o r m a t i o n boundary. The information boundaries of groups and higherlevel systems have special characteristics that result from the fact that components of such systems lack physical continuity and can separate from other components. The boundary configuration shifts as members move from place t o place. People who are not group members may mingle with those who are. Like the matter-energy boundary, however, the information boundary is a physical reality. It is the outer limit of the region over which group information can flow at a given time, whether or not all channels are currently active. When all members of a family are

BOUNDARY together in their home, or when a social group i s assembled, t h e information boundary can coincide with the mattere n e r g y b o u n d a r y . W h e n a son o r d a u g h t e r i s a w a y a t college, a club member is in the hospital, or members of a work group are too far apart for faceto-face conversation, they can remain within t h e information boundary by u s i n g walkie-talkies, telephones, o r other communication media. Parties of m e n on t h e moon h a v e m a i n t a i n e d contact with o t h e r members of t h e i r group in mission control. Also, during absences from the group, a member can remain within the information boundary by storing coordinating data in memory. An example is an agreement t o carry out a planned activity and then rendezvous a t a given spot or a t a given date. A person can be within the territory of a group and interact with group members without necessarily being within its information boundary. One does not become a member of a family, a work group, or a social group by entering its home, office, or meeting place. Visitors, customers, or technicians who come t o repair one of the group’s artifacts are, in our terminology, inclusions in the group but not members. Information the group does n o t w a n t t o become known i s filtered before i t can reach such outs i d e r s . Children a r e told not t o tell s t r a n g e r s w h a t goes on within t h e family, and are often instructed t o pay no attention to what such people say. Some social groups, like fraternities and sororities, have secret symbols known only t o t h e initiated. Being “in” t h e living system involves being within its information boundary and participating in t h e group information exchange, a process of t h e c h a n n e l a n d n e t s u b system. Many of the communication channels used by groups are upwardly dispersed to components of the channels and nets of organizations, communities, or higherlevel systems. LST regards money as a special form

Behavioral Science, Volume 37,1992

33

of information which is protected by a system’s i n f o r m a t i o n b o u n d a r y . A banknote i s valuable because of t h e buying power it represents, and not for the intrinsic value of the paper marker. H u m a n components a r e expected t o m a k e s u r e t h a t only authorized a n d reliable people receive the group’s money and that it is not stolen or lost.

BOUNDARY PROCESSES AT THE LEVEL OF THE ORGANIZATION Matter-energy b o u n d a r y . T h e d i s tinction between t h e boundary of t h e living system and the perimeter of the system’s territory that was made above in t h e discussion of t h e group i s also valid for the organization and at higher levels. Large organizations often have several geographically separate offices, p l a n t s , c a m p u s e s , o r b a s e s , e a c h of which h a s a matter-energy boundary surrounding living components of t h e organization and artifacts such as fences or walls a t the perimeter of its territory. I n f o r m a t i o n flows c o o r d i n a t e t h e s e separate components as they do a t lower levels. An i m p o r t a n t b o u n d a r y f i l t e r i n g process in organizations is screening proposed new members or employees. Membership committees, recruiters, and employment offices c a r r y o u t t h i s process. Admitting offices in hospitals screen patients who, if admitted, will be inclusions in the system, not members. R e g i s t r a t i o n d e s k s perform s i m i l a r functions for hotel guests. Other components filter people a n d o t h e r m a t t e r - e n e r g y a t e n t r a n c e s or exits by asking for passwords, examining passes o r badges, or refusing t o allow certain artifacts o r materials t o be brought in. Museums, for example, often require that umbrellas and cameras be checked a t entrances. The boundary process of protection in organizations i s carried o u t by such living components a s night watchmen, armed guards, and personnel who check

34

MILLERAND MILLER

baggage for weapons or bombs. Guard dogs warn of intruders on the organization’s territory. Artifacts such as electric fences, security alarms, the electronic devices that detect weapons before they can be carried onto planes or the metallic tags on g a r m e n t s t h a t s e t off a l a r m s a s shoplifters leave stores are important nonliving components of t h e matterenergy boundary of organizations. Upwardly dispersed components of the matter-energy boundary include community police who come when a security a l a r m sounds, or who protect t h e organization’s territory during a strike. Information boundary. Members or employees of an organization are within an information boundary which, like the information boundary of a group, exists as long as communication is possible among them. They remain within this boundary even when they do not have access to a communication channel, if coordinating information is stored in memory. The crew of a destroyer that has lost radio communication with the other ships in its battle group is outside t h e information boundary t h a t h a d included them. Standard procedures for such situations stored in memory may help a destroyer t o maneuver in such circumstances. When a factory is closed for the night, certain employees remain inside t h e boundary because they are “on call” with beepers to alert them if they are needed. Others go outside t h e information boundary when they leave the organization’s territory. When a person joins an organization he crosses its information boundary by being made aware of policies, practices, o r technical information t h a t is not shared with outsiders. He or she may have to swear not to divulge industrial or fraternal secrets. “Kiss and tell” books by former White House employees violate this boundary. Guards who examine briefcases of exiting personnel to be sure industrial

Behavioral Science,Volume 37,1992

secrets are not being carried home at night are components of this boundary. So a r e the technicians who maintain boundary artifacts like radios. Money and other forms of monetary information a r e filtered by special boundary components such as internal accountants a n d bookkeepers who observe discrepancies in the books and report possible theft. Executives who authorize payments to creditors are also components. Outside accountants, bank examin-ers and armored car services are examples of dispersed components of this boundary.

BOUNDARY PROCESSES AT THE LEVEL OF THECOMMUNITY

Matter-energy boundary. Communities are villages, towns, cities, counties, states, provinces, and similar political units in which people live together and satisfy their daily needs. The subsystems of communities are made up of organizations. T h e i r s u p r a s y s t e m s a r e societies. Their deciders are political organizations, or, in smaller communities, groups. Among the relatively few components of the boundary subsystem at this level are state or provincial agricultural departments charged with preventing imports o r exports of f r u i t s a n d vegetables t h a t might be carrying disease or insects. Communities threatened by wildfires are defended by fire d e p a r t m e n t s with t h e assistance of volunteers from the community. When a n epidemic occurs i n a society t h e health departments of communities may provide vaccinations t o prevent disease from ravaging their citizens. Under some circumstances police patrol roads leading into communities t o apprehend people who can harm the community in some way. The living system of a community consists of the organizations that make up its subsystems, and the groups and individuals who reside in it. As at other multiorganism levels, the boundaries of

35

BOUNDARY the living system may not be the same as its territorial borders. Rather, the boundary of t h e living system is the outer limit of the spatial distribution of its components at any time. Ancient cities were surrounded by walls with sturdy gates t h a t could be closed a t night to protect a g a i n s t invaders and undesirable visitors. The remnants of old walls can be seen in present-day Rome, Paris, a n d other cities with long histories. Modern communities are not protected in this way. The governments of some cities or villages, however, try to exclude people that fit into certain categories, such as “likely t o need welfare”, or “vagrant”. Recently a n American city tried, unsuccessfully, t o exclude homeless people by passing a law against sleeping outdoors. The territorial borders of communities a r e established by law in most modern societies and formal procedures, such as approval by t h e larger community or the society of which they are components or a vote by citizens, must be undertaken to change them. Territorial borders may be marked by signs saying “City Limits”, or “Welcome, you are now entering Ohio. The speed limit is...” It is not unusual for cities to annex many square miles of land surrounding them to control growth and development and extend their tax base. Their “city limits” signs are then placed far outside the center of population. Territorial borders commonly mark the limits for many kinds of matter-andenergy flows. Roads a r e maintained only t o t h e s e limits by community employees using t h e community’s equipment; public services like water mains, sewers, garbage a n d t r a s h collection and electric lines extend only this far. I n some places movement of certain kinds of agricultural products into or out of a community is forbidden or limited, a boundary filtering process. If, for example, fruit flies are found in a s t a t e , it may not be allowed t o ship

Behavioral Science,Volume 37,1992

produce susceptible t o damage from t h e m over its borders. T h e s t a t e o r provincial organizations responsible for agricultural inspections are boundary components t h a t perform a filtering process. People are usually free to cross these borders as they wish, although in some societies certain communities restrict movement of residents out of the system and are closed to visitors from outside. Information boundary. Components of communities are within a network of formal and informal communication and monetary exchanges, the outer limits of which are the information boundary of the system. At this level most kinds of information are usually allowed to flow freely across boundaries. The information boundaries of communities may, however, be more selective in filtering certain types of information than those of the society as a whole. Cities try to prevent certain types of films and books from being shown or sold within their boundaries. “Banned in Boston” was at one time applicable to plays that were considered acceptable in other parts of the society. The borders of a community’s territory a r e limits to some k i n d s of information flows. People on one side pay t h e i r local o r s t a t e t a x e s to a different governmental unit than those on t h e other. Traffic laws a n d local ordinances often change at state or city borders. Money belonging to the community is filtered by boundary components similar to those at the organization level. BOUNDARY PROCESSES AT THE LEVEL OF

THE SOCIETY

M a t t e r - e n e r g y b o u n d a r y . “Uncle Sam”, “Mother Russia”, t h e “Fatherland”, “La Belle France”, and other such designations a r e personifications of systems for which many of their citizens are willing to die. In this age of nationalism, a much greater proportion of the

36

MILLER AND MILLER

wealth and human energy of societies is devoted to boundary subsystem processes of societies than to those of communities or supranational systems. At no time in history, however, whatever form of government was current, have t e r r i t o r i a l boundaries been immutable, although some societies have been more stable than others. By treaty, purchase, o r conquest, some societies expand, others lose parts of their land. The map of the world is out of date every few years. A society’s territory need not be spatially continuous. Alaska is separated from “the lower 48” States of the United States by Canada. Hawaii lies more than 2,000 miles from t h e m a i n l a n d , separated by international waters. The flag of Great Britain flies over distant lands, including the Falkland Islands-a third of t h e way around t h e world from t h e British Isles. Several other nations are also divided in this way. Nations with geographically separate parts ordinarily have a different set of boundary components assigned to each. As a t other multiorganism levels, the matter-energy boundary of t h e living system r a r e l y coincides with system territorial borders. I t s characteristics a r e like those of other multiorganism systems. The boundary of a society is the outer limit of the spatial distribution of the society’s living components. If these change t h e i r distribution within t h e territorial borders, the boundary changes its shape. C o m p o n e n t s of t h e m a t t e r - e n e r g y boundaries of societies include fortified cities on t h e b o r d e r , o r g a n i z a t i o n components like a r m i e s , c u s t o m s services, inspectors for drugs and other illegal or dangerous imports from outside the society, and immigration services. Some of these are aided by drug-sniffing dogs. Much more e m p h a s i s i s placed by most modern societies on filtering people and materials entering the system than on those leaving it, although there are

Behavioral Science, Volume 37,1992

exceptions. Among t h e many artifacts used a t this level are customs gates and structures, guns a n d a r m a m e n t s , a n d Coast Guard ships. Information boundary. The informa t i o n b o u n d a r y of societies f i l t e r s information t h a t enters and leaves the system. This boundary is n o t co-extensive with the matter-energy boundary since it surrounds components t h a t are out of the system’s territory so long as communication channels exist o r they r e m a i n coordinated by s t o r e d information. Organizations a n d individual citizens t h a t have remained in foreign places for a long t i m e , however, can become so integrated into another society that they “lose touch” and are no longer within the information boundary of their society. Diplomatic personnel stationed abroad a r e moved frequently t o avoid this. Many societies exercise strict control over information flows t o other parts of the world. Intelligence organizations try t o k e e p foreign s p i e s from l e a r n i n g military a n d industrial secrets and, in their turn, spy on other societies. Both incoming and outgoing news is censored in parts of the world. Other information, like certain books and films, may also be stopped by c u s t o m s officials a t t h e b o r d e r . A n o t h e r form of b o u n d a r y filtering is more subtle. Citizens may be t r a i n e d t o d i s r e g a r d , disbelieve, or disapprove of certain ideas, so that even if the markers that carry them cross the society border, t h e ideas a r e not propagated through the channel and net of t h e nation t h e y e n t e r a n d have little effect on the behavior of components.

BOUNDARY PROCESSES AT THE LEVEL OF THE SUPRANATIONAL SYSTEM Matter-energy boundary. S u p r a national systems are associations of two or more societies (nations in the present world) which, i n t h e p e r s o n s of r e p r e s e n t a t i v e s o r d e l e g a t e s , m e e t in assemblies, organizations, councils, or

BOUNDARY other bodies to find solutions to common problems or to attempt to meet emergencies. We make a distinction between supranational systems and international systems on the basis of their decider subsystem structure. The decider subsystems of member societies of supranational systems relinquish some of t h e i r power to t h e decider of t h e supranational system, which forms an echelon above that of member deciders. This is not true of international systems. The borders of some supranational systems, like the European Community, a r e continuous around contiguous member societies. Members of others, like NATO, are separated by nonmember nations or i n t e r n a t i o n a l waters. Separate components of their boundaries surround each of these. The United Nations, with member nations in all p a r t s of t h e world, comes close t o including the entire world within i t s boundaries. The territorial borders of supranational systems change when the borders of member nations change, as for example, when a disputed province is taken over by one claimant by force or agreement. Some s u p r a n a t i o n a l systems a r e permanent organizations with offices or other buildings in member countries on land that is considered to be under the control a n d protection of t h e s u p r a national system. These offices have an extraterritorial status somewhat like that of embassies. Supranational systems of the modern world a r e far from totipotential a n d much less powerful than the sovereign nations that compose them. Boundary processes at supranational borders are usually downwardly dispersed t o the society whose territory is being entered or left rather than being carried out by the supranational organization to which the society belongs. Customs officers, immigration officers, police, and military personnel a r e employees of the local member nation r a t h e r t h a n t h e supranational system as a whole. They

Behavioral Science,Volume 37,1992

37

filter matter-energy, such as tourists or agricultural products, according to the laws and regulations of the society. Membership in such supranational systems tends to weaken societal boundaries. Citizens of each of the member countries of the European Community a r e allowed to e n t e r all t h e o t h e r s without formalities. Imported a n d exported goods passing from one country to another are not subject to tariffs. This, however, is by no means t r u e of t h e United Nations or various other supranational systems. If mutual defense pacts or treaties establish a supranational decider such as a commander-in-chief above t h e top military officers of member nations, boundary protective processes are under s u p r a n a t ion a1 con t r 01. NAT 0 h a s international military forces that protect its member countries. The North American Air Defense Command, made up of units of United States and Canadian armed forces under joint command, is on continual a l e r t t o defend t h e two participant societies. In addition, the United Nations can, under orders of the Security Council, assemble a military force made up of u n i t s of t h e armed services of cooperating countries t o defend o r police troubled areas of the world. United Nations forces under joint command at various times have fought in Korea and policed the border between Israel and Syria. A commander-in-chief also directed multinational military operations in the Gulf War. Information boundary. Most information boundary processes at this level are downwardly dispersed t o member societies. The greater strength of national, as compared to supranational, information boundaries prevents even members of close alliances from trusting one another completely. This is abundantly documented i n t h e memoirs of Peter Wright, a former official of the British counterintelligence service (Wright, 1987) who made i t clear t h a t secret intelligence information was shared by

MILLER AND MILLER

38

the British with the similar American and French agencies only partially and grudgingly* The organizations that do the work of supranational systems, like the many autonomous organizations of the United Nations, protect t h e i r confidential information in the same way that other organizations do. Boundaries to monetary information are downwardly dispersed to member societies, which enforce currency control regulations a t their own borders. At present there is discussion among the countries in the European Community as to whether the currencies of member nations should replaced by a common unit, t h e ecu, controlled only at t h e overall supranational boundary. REFERENCES

Bean, B . Geotactic behavior of C h l a m y d o m o n a s . Journal of Protozoology, 1977, 24, 394-401. Bretscher, M. S. The molecules of the cell m e m b r a n e . S c i e n t i f i c American, 1985, 253 (4). Catterall, W. A. The molecular basis of neuronal excitability. Science, 1984, 223, 653-660. Detweiler, D. K. C i r c u l a t i o n . I n : Brobeck, J. R. (Ed.) B e s t &

Behavioral Science, Volume 37,1992

Taylor’s Physiological Basis of Medical Practice, 1973, 3-27. Goldstein, G. W. & Betz, A. L. The blood-brain barrier. Scientific American, 1986, 255(3), 74-83. Hudspeth, A. J. The cellular basis of hearing: the biophysics of hair cells. Science, 1985, 230, 745752. Inoue, T. & Nakoaka, Y. Cold-sensitive responses i n t h e paramecium membrane. Cell Structure and Function. 1990, 15, 107-112. Miller, J. G. L i v i n g s y s t e m s . New York: McGraw-Hill, 1978. O’Brien, D. F. The chemistry of vision. Science, 1982, 218, 961-965. Spector, R. & Johanson, C. E. The m a m m a l i a n choroid plexus. Scientific American, 1989, 261, 68-74. Stevens, C. F. Biophysical studies of ion channels. Science, 1984, 225, 1346-1356. Wright, P. Spycatcher. New York: Viking Press, 1984, 146. (Manuscript received November 1991)