THE NATURAL BASIS
THE BRAIN--PART 1
The brain of man is the most wonderful mechanism created by the Lord in ultimate nature
270. When we look at the brain from the scientific point of view, the huge number of its nerve cells and the complexity of the links between them are sufficient to arouse wonder. Estimates suggest a total of 2,600,000,000 to 14,000,000,000 nerve cells in the cerebral cortex, each of which is connected to about 600 other nerve cells.
271. The nerve cells are known as neurons. For further
information about cells in general and neurons in particular see Martin
M. Echols, "The Cortical Gland and its Relationship to the Modern Neuron"
(Echols, 1980 B, p. 104). The neuron is the essential living cell out of
which nerves are made. An orderly massing together of millions of neurons
and their supporting cells, called glial cells, makes the brain. Glial
cells are also known as neuroglia. They are very important for maintaining
the proper conditions for the functioning of the neurons. Each neuron can
receive electrical impulses from other neurons and pass impulses to still
others (few or many in each case). The impulses are not like an electric
current but only localized changes in electrical status. They pass from
neuron to neuron along very fine threads. Some neurons are shaped like
whole trees; the trunk being the cell body, the branches being sending
threads (called axons), and the roots being receiving threads (called dendrites).
272. We have mentioned above only a few of the interesting
things that have been discovered in this century about the brain, but the
smallness of the units and their complex linkings are almost beyond apprehension.
What is the result of fourteen thousand million units connected each one
to six hundred others? Very much more than 600 x 14,000,000,000 for there
is a complexity which requires its own type of mathematics or language
or symbolism. In addition there is the cerebellum in which the neurons
are even more numerous. The cerebral medulla also contains groups of neuron
bodies besides the fibres of which it is usually said to consist. These
marvelous results of prodigious scientific labor leave us still absolutely
ignorant of the soul. All we have are fantastic weavings of minute electrical
changes. Obviously life itself eludes the instruments of science.
273. Of course, it almost goes without saying that the brain is unimaginably
complex, since all the complexities of human behavior originate in, or
are mediated and directed by, that organ. These however are familiar wonders.
Less familiar, and therefore more apt to arouse astonishment, is the knowledge
that the brain communicates with heaven. For this reason, it is the pinnacle
of creation (Berridge, 1979 A, p. 61). The fact, however, ought not to
be unfamiliar. It is well known that love is heavenly, and that it is experienced
in the brain as love and expressed in the natural world of earthly things
by means of the brain acting through the body (See, for example, Nos. 5-10
above). The experience is familiar; nay, it is more; it is a continuous
necessity of life. "Love is the life of man" (DLW 1). It is, however, the
Word of the Lord that unites heaven and earth.
274. In AC 4041 we are told that "the heavenly form
is amazing and quite surpasses all human intelligence." Thus, not unexpectedly,
puzzling things follow: gyrations, circumvolutions "seen in the human brains,"
and a flow (i.e., gyrations) which assured Swedenborg that the brain is
formed "in accordance with the form of the flow of heaven." This is enigmatical,
but the angels informed him "that man is a little heaven in the least form."
We feel this is more understandable (until we begin to analyze it) and
it seems possible that the abstruse quality of the description of flows
and gyrations was due at least in part to the limitations of natural knowledge
and language at that time. As has been pointed out (Alden, 1979, p. 356),
we think now of brain function in terms that fit our observations better,
namely, electrical potentials, computers, holograms, and so on. But still,
this is really nothing to do with the question. This is merely the mechanics.
The question really concerns the heavenly form; and possibly the natural
terms describing shapes and flows act as cherubim of the literal sense
of the Word (AC 308). This
275. It is a characteristic of human development that a beginning has to be made with sense experiences of concrete things (No. 42). From these we can move gradually to spiritual things. There is always a higher level to which we can hope to climb. There is always a lower level to which we can look for representations and correspondences and thereby confirmations. So it is that, although the interior things of the brain, which are in accordance with the interior forms of heaven (AC 4041), are quite incomprehensible, there are lower corresponding things through which useful ideas may be obtained (AC 4043). This we have already seen in a small way just above (No. 274).
&276. The representation of spiritual things by the bodily acts they cause was mentioned earlier, and it is obvious that the brain, although part of the body, is the link between the spirit and the body. The action of nerves on muscle was used as an example to show how two things so different as to appear to have nothing in common can yet correspond so well that one controls the other (No. 7). As the brain is nothing but nerves and their supporting tissues, the correspondence between the brain and the body is like that between nerves and muscles. The correspondence is perfect; the difference is enormous. That thing in the brain (i.e., love?) that makes the mother smile bears no resemblance to a smile. Its physical form is merely a storm of tiny electrical impulses (Sir Charles Sherrington, quoted by Allen, 1982, p. 138). In this example we have climbed, as it were, from one physical form (the smile) to a more interior one which corresponds (the nerve impulses), but they are still both physical. Hence we have taken but a very small step on the ladder of Jacob, but the Writings teach us to take further steps. It is said that the subsistence of one thing is from another, this one from still another, till all subsist finally from the First, "and this by a connection of correspondences." Thereby we may know "that there is a correspondence between man and heaven; and further between heaven and the Lord who is the First" (AC 4044).
&277. These preliminary considerations are specially important in a study of the brain because the brain is the home of man's spirit, the form of heaven, a house of heaven on earth where the man may dwell, and the place where even the Lord may come to be with him. As it is in the form of heaven, we cannot appreciate its form and beauty without bearing in mind something of what has been revealed about heaven.
&278. The most important and interesting parts of the brain are the neurons or nerve cells, those highly specialized units which all affect each other, and which seem to be responsible for remembering, thinking, and controlling the body (No. 271). These are delicate cells which need special protection and care besides the merely mechanical protection of the skull. There are, therefore, in the skull, a number of accessory structures that may be considered part of the brain, inasmuch as they are essential for its welfare and maintenance. Figure 15 provides an illustration of these accessory structures, or meninges, discussed in the numbers following this. The first and most external of these is the Dura Mater. It is a thick, dense membrane which encloses the whole of the brain and spinal chord.
&279. It seems strange that in an account of the brain we are told of external kinds of spirits who relate to a part of the dura mater and who "wend their way more and more outward, even to the outer skin of the head, which they represent" (AC 4046, emphasis added). It is strange, because the dura mater lines the inside of the skull and is not the outer skin. Nevertheless, "wend their way outward" can be explained very simply. It is apparent to the reader of AC 4046 that the dura mater consists of two layers, and we are here concerned with the outer one. This is applied closely to the inside of the skull, for it serves to supply nourishment to the growing bone. The dura mater extends even over the edges of the plates of bone that form the skull, and before they knit together the dura is continuous with the membrane that covers the outside of the skull. So we have a neat representation of the way those external spirits can move away from the internal things corresponding to the brain. As a man ages, the bones of the skull knit together, and the outer layers of membrane become more isolated. So such spirits may move further away until they represent merely the outer skin.
&280. Those who relate to the inner layer of the dura mater are slightly less dense, but still they had been unable to penetrate further than natural things. As they had been good citizens, had worshipped the Divine and "said their prayers," they belonged to the Grand Man (as do even those who relate to the outer skin).
&281. The quality of this whole group is easily seen as represented in the dura mater, for even the inner layer is relatively external, sending no fibres into the brain, and being separated from it by the pia-arachnoid (see No. 284) and cerebrospinal fluid. The dura mater supports and protects. It is dense and thick. Its use is as important as the tissues it protects, and the people who correspond to it are similarly important.
The upper central
portion of a coronal section of the skull and brain, including the cleft
between the cerebral hemispheres. As shown, the cleft and the space between
the skull and the brain are occupied by several membranes. The width of
the cleft between the hemispheres has been exaggerated for clarity. It
is considerably narrower than shown. (Compare Figure 16)
Sources: Gardner, Gray and CXRahilly, Anatomy: A Regional Study of Human Structure, fig. 53-15; Wilson, Human Anatomy, fig. 12-5; Anthony and Kolthoff, Textbook of Anatomy and Physiology, fig. 8-1; Gardner, Ernest, Fundamentals of Neurology, fig. 7-2.
&282. Having seen how easily "wend their way more and more outward" is explained in anatomical terms, we are hopeful that it will not be too long before we are also able to understand the references to pulsations and undulations and various lights. We cannot yet easily explain all these things, but hints of solutions are already extant. Why, for example, was there a light "gross but not yet luminous," "dim and yet flaming, not bright"? Perhaps the anatomy of the optic nerve provides the answer. The dura mater extends as a sheath around this nerve and blends in front with the sclera or outer coat of the eyeball. Other nerves are said "to pierce" the dura mater as they pass from the brain through the skull (but it is more correct to say that the inner layer of the dura mater becomes continuous with the ordinary nerve sheath, which is obviously a different structure). It has been explained in a previous essay, that the retina is to be regarded as part of the brain (Berridge, 1980 B, p. 68) (see also Chap XV), and that even the coating of the brain extends as far as the eye. This special relationship was indicated by the light Swedenborg saw, and its dimness showed that it was only the outer layer of the eye to which those spirits corresponded.
&283. It is important to add here that the nerves which "pierce" the dura mater do not include the olfactory nerve. This has a special anatomy of its own, which is reflected in comments about it in the Writings. The agreement between the Writings and modern ideas is more than might be gathered from a mere consideration of excretion of brain fluid into the nose. We return to this theme below (Nos. 295-298).
&284. Beneath, i.e., inwards from, the dura mater is the arachnoid mater, which is a delicate membrane lining, as it were, the whole of the dura mater. Below the arachnoid is a space filled with cerebrospinal fluid and bridged by fine threads (hence the term 'arachnoid'). Next is the pia mater. This also is a delicate membrane and it is very important as it carries many blood vessels and dips with them into the clefts of the brain. This is noted in AC 4047, where the pia is said to communicate with the cerebrum and cerebellum by emitted threads. We read here also that the pia "is the second integument more closely investing" the brain; whereby a first integument more closely investing is implied. This is clearly the arachnoid, for the dura does not so closely invest. The arachnoid is mentioned in Inv. 49 as one of three tunics which cover the brain. Here, in AC 4047, it is not mentioned separately, and this need not surprise us, as it is closely related to the pia both phylogenetically and embryologically (though one imagines this was not known in the 18th century). The two membranes are now often classed together as pia-arachnoid and the space between them is regarded as part of the single structure. The same membranes extend round the spinal cord but there are differences in detail.
&285. The spirits of this region were they who
did not trust much to their own thought but depended on the belief of others
(AC 4047). Thus they lacked self-confidence in spiritual matters. Such
people can be useful in heaven where they receive a good influx, though
at risk elsewhere. (The pia-arachnoid would not be serviceable except to
the brain and when protected by the dura and the skull). Their ideas were
readily opened, they easily received influx, and they were modest and peaceful.
As the pia-arachnoid is serviceable to the brain, keeping it in a healthy
and active state, so are these spirits to the angels of heaven. Their peace
and modesty also agrees with the delicate nature of the pia. We are told
that they could serve the angels as mediums, and although it is not categorically
stated that they are intermediate spirits through whom communication between
the heavens takes place, we are led to think that communication is one
of their functions. (See AC 9670 regarding conjunction between the celestial
and spiritual heavens.) These ideas lead one to ask what corresponding
communication there can be by
&286. When one thinks of communication in the brain, one's thoughts immediately fly to axons and dendrites through which the neurons and groups of neurons communicate with each other (No. 271). This does not happen in the pia mater. A hasty reader of the AC might think he has found an error, but there is no error. The communications that take place via the pia-arachnoid are those that depend on the blood, for most of the blood vessels supplying the brain divide in the pia before sending vertical branches down into the cortex. Thus all the nourishment and any hormonal influences come through this route. Another communication is that of the sympathetic nervous system which has fibres extending to the branches of the arteries in the pia. These fibres presumably control the arterial tension and hence the blood supply through the various branches, but even now the innervation of these arteries is not well understood. These, then, are the kinds of communication that correspond to those of the spirits of the province of the pia mater. It is credible that such relatively simple spirits, with no confirmed opinions of their own, should aid in a general type of communication and provide simple services. These things are easily seen to correspond to the way the pia-arachnoid provides services for the brain.
&287. The spirit who is described in the next number of the Arcana (AC 4048) was, like those of the pia mater, in a peaceful state, and, like them, he could accept and bring forth what the angels said. (Here, however, "interior" angels; in AC 4047, "angels.") No connection with the pia-arachnoid is mentioned, in spite of the similarity. There is, however, a close connection. Spirits like the one in question relate to the longitudinal sinus (now called saggital); a long, wide blood vessel like a vein, but bigger, and running above and partly within the cleft that is between the cerebral hemispheres. Now called the superior sagittal sinus, it is one of a number of large vessels into which the venous blood from the brain (i.e., the `used' blood) is collected on its way to the internal jugular veins and hence to the heart. Like several other sinuses, this one is between the two layers of the dura mater, but its connection with the pia arachnoid is through the arachnoid granulations. These appear, in a dissected specimen, as small nodules on the inner surface of the longitudinal sinus, so that they project into the blood itself during life. A sketch of them is to be seen in a communication by Pacchioni, but it is to modern works that we turn for details of their structure and function. They are found to be stalk-like outgrowths of the arachnoid which push through the inner layer of the dura mater and into the venous sinus where they expand into knob-like projections. Since the arachnoid is mostly space containing cerebrospinal fluid, it will be seen that these projections bring the cerebrospinal fluid into close proximity with the blood in the sinus, and it is here that the fluid finds its way back into the blood. Observations with the electron microscope (on sheep) indicate that fine tubes perforate the granulations, allowing the fluid to escape, as if they were valves. This is reminiscent of that spirit's statement that if anything not good and true flows in, he does not admit it or utter it. In a parallel passage (AC 7744), he is said to admit it but not to utter it.
&288. We have seen that the pia-arachnoid forms a layer containing
spaces filled with cerebrospinal fluid. This same fluid also fills the
hollow parts inside the brain, i.e., the ventricles. See Figure 18. All
the ventricles communicate with one another, but the communication with
the pia-arachnoid space is through the last, or fourth, ventricle only.
The cerebrospinal fluid is secreted into the ventricles, whence it can
pass into the pia-arachnoid by way of openings in the roof of the fourth
ventricle. Some of the structures which produce the fluid (i.e., the choroid
plexuses) are in the lateral ventricles and these ventricles extend some
way forwards into the cerebrum so that the fluid secreted by them must
flow "from the front backwards" (as in AC 4047) in order to find its way
out. After this, the cerebrospinal fluid flows upwards and then forwards
and sideways beneath the cerebrum. Finally, it climbs over the outer surfaces
of the cerebrum and then over their upper surfaces to the middle line where
is the longitudinal sinus, through which it returns to the blood stream
as mentioned above (No. 287). This last flow is "from each
&289. The flow of cerebrospinal fluid takes place partly because it is produced in the ventricles and passes into the blood stream in the longitudinal sinus. It is also moved partly by the cilia (waving fibres) on the surface of the cells that line the ventricles. Thus we need not think of the spirits of this region as if they were themselves flowing like fluid and we may prefer to regard them as corresponding to the living cells that contribute to the movement. Thus it is not said "they flowed" but "whose common action…flowed" and "whose inflowing action was" This might seem to contradict the reference in AC 4049 to "the nature of the better kind of lymph"; on the other hand, in literature, the tool is often mentioned in place of the user--a hammer for the smith, a sword for the soldier, and it is ordinary usage to speak of the violins of an orchestra. These examples are similar to the naming of a vessel to signify the contents. The point is that cerebrospinal fluid is a relatively simple liquid, devoid of living cells, whereas the flowing action refers to living spirits.
&290. A consideration of the spirits that relate to the ventricles (AC 4049) leads us into a difficult area when we try to understand what is meant by "the better kind of lymph which is there." It is clear from AC 4050 that, in the terminology of the Writings, there can be a number of lymphs. Because "lymph" now has a specific meaning, perhaps we should think of them merely as liquids, or perhaps several "lymphs" could be together as constituents of one fluid. This was suggested in an earlier article (Berridge, 1979 A, p. 61), because there is only one fluid in the brain cavities. In the same article, an attempt was made to explain the meaning of "it is the nature of the better kind of lymph which is there to return into the brain" (AC 4049). This was done by pointing out that diffusion, i.e., the random motion of molecules, causes constituents which are disappearing at any point (being used, for example) to seem on the whole to move towards that point, because there are none to move away (Balls in random motion on a billiard table would all finish in the pockets). Similarly, molecules which are being produced at any point will diffuse away from it toward a point at which they are being consumed. This could explain why the better kinds, or those of use, would move into the brain and the worse kinds would move out. However, it is generally accepted that the nutrition of the brain is through the blood stream and that its waste products are carried away in the blood. There is no lymphatic system in the brain. The waste products which are too large, molecularly speaking, to pass through the walls of the capillaries, are dealt with by the glial cells, whose functions are the maintenance of the neurons in a healthy condition. There are practically no large molecules in the cerebrospinal fluid, which does not act as a means of disposing of them (contrary to what was suggested in the earlier article (Berridge, 1979 A, p. 61)).
&291. The function usually ascribed to the cerebrospinal
fluid is that of supporting the brain tissues by reducing their weight,
since they almost float in it. Other functions, however, are possible.
It is said that certain cells are associated with secretion into and uptake
from cerebrospinal fluid but no facts about this are reported. It has also
been shown that quite large molecules injected into the ventricles can
diffuse through the brain tissue right across to the pia mater (but not
into the blood capillaries of the brain). Thus there is some experimental
support for the suggestion that diffusion would account for substances
getting into the brain if they were being used up. Such a movement would
occur unless the fluids inside and outside were exactly the same.
The fluid inside is produced by seepage through the capillary walls (but
see No. 300 concerning the blood-brain barrier), and it is modified in
its composition by activities of the glial cells (No. 271). On the other
hand, the fluid outside is the cerebrospinal fluid (See no. 284). It is
produced largely by the choroid plexuses, and its composition is different
from a filtrate
&292. The structure of the brain would allow fluids to move between it and the fluids contained in its cavities or ventricles. We are as yet unable to identify any component whose nature it is to return into the brain. However, there is another way of looking at the problem.
&293. We are often told (e.g. in AC 4043) that
the things of heaven are incomprehensible and unutterable. In order that
Swedenborg might be able to comprehend them and utter them, i.e., write
about them, they had to be expressed in representatives "by means of forms
to which the forms seen in the world bear some resemblance" (AC 4043).
These forms were necessarily the mental concepts that Swedenborg had in
his own mind. As already argued above, such forms were also those of his
contemporaries, in order that the Writings could be understood (even if
only by a few). We believe that the wisdom of the angels with whom Swedenborg
conversed, and the truths revealed to him by the Lord, correspond to natural
things as they really are, so that the truths are in agreement with modern
science (except when science is in error). There are changes
&294. There are many passages in the SD that
are difficult to understand from the scientific point of view, and perhaps
this is why the Lord delayed their publication. On the other hand, we find
comments which are highly interesting. We read, for example, (SD 830) that
the fluids in the ventricles flow from between the fibres of the brain
"and from elsewhere." We now know that "elsewhere" are the choroid plexuses,
which are largely responsible for the production of cerebrospinal fluid.
In SD 831, part of this fluid is said to be absorbed by the choroid plexus.
This is remarkable, because the fine structure of part of the choroid plexus
is like that part of the kidney that absorbs water from the very dilute
urine produced in the renal corpuscles. (As a first approximation we may
say that urine is produced by filtration from blood followed by re-absorption
of much water and other useful substances.) Further, the fluid produced
by the choroid plexuses is not merely a filtrate. This is deduced from
&295. We turn to this subject here because its relationship to the brain led Kenneth J. Alden to include it in his study of the brain (Alden, 1979, p. 358). In that very useful work, he shows that Swedenborg was limited to the science of his time. This is an important concept that we have already had occasion to emphasize. Alden's contribution encourages one to think around that limitation and to realize the chaos that could have followed if it had not been observed. The interest has always been in showing the miraculous nature of the revelation granted through Swedenborg, and it is characteristic of enthusiasm that it tends to blur distinctions and overstep boundaries. We know that Swedenborg himself was anxious that he should not be worshipped, almost as though he foresaw that men might regard him as infallible. So we are able to detect "errors" in the Writings, and having accepted that they were inevitable, we can marvel at how few they are, and turn again to the remarkable evidences of special enlightenment even in matters of science. This enlightenment appears to have taken the form of a bias towards the less incorrect notions of that time. The ascribing of an excretory function to the mammillary processes is a case in point (AC 5386).
&296. Alden "discovered" that mammillary processes used to mean olfactory nerves (or, more precisely, the olfactory tracts, as pointed out in his more detailed but unpublished notes on the subject (Brown, 1979, p. 356)). This proves to be particularly helpful because what are now known as mammillary bodies are quite different structures of the brain some distance away. The term "mammillary processes" is not now used. Thus it seemed, before Alden pointed out the contrary, that the two terms might mean the same. This made the beginning of AC 5386 impossible to understand. Now, however, one can at least see the origin of the comments there.
&297. As Alden has also demonstrated, Swedenborg formed his own opinions, although he was obliged to rely largely on the anatomists of his time. Now, however, their methods have no special claim to our respect. Some of the experiments quoted in The Cerebrum (Swedenborg, 1938) now seem crude and sometimes self-defeating. We have no qualms about differing from Vieussens as Swedenborg also did on occasion (Brown, 1979, p. 356).
&298. According to the account given in Gray's Anatomy (Williams, 1973), there is continuity of tissue spaces between the nasal mucous membrane below and the pia-arachnoid round the brain above, and so, even to the ventricles, as explained above (No. 288). In cases of injury this allows access of infection to the brain, and it has been thought that the germs of meningitis can spread along this route, but this has not been conclusively demonstrated. It is clear, however, that cerebrospinal fluid can move into the tissues of the nose, and if there is injury it escapes. When one remembers how common bleeding from the nose is, one realizes that a slight escape of cerebrospinal fluid may also be quite common. We return to the subject in more detail in a later chapter. Meanwhile, it seems possible that the spiritual anatomy known to the angels would bias Swedenborg towards the thought of fluids in the nose descending from the brain. Phlegm is another thing!
&299. It is a horrible matter to contemplate the presence of phlegm
in the beautiful and delicate structures of the brain. The very horror
of it suggests equally horrible spiritual things. Hence we are grateful
to Alden for having endured the horror and for making his conclusions available
(Brown, 1979, p. 356). He points out that in those days, unhealthy cadavers
were often used for dissection, and that hygienic conditions seldom prevailed
(if ever?), so that pus and other viscid substances might have been mistaken
for phlegm, or merely have received that name. These comments are essential
knowledge for translators; indeed for all who would understand the AC rightly.
Such comments lead us to remember that the experiences we read about in
the Arcana took place before the Last Judgement, as also noted by Worcester
(1899, pp. 403 and 405). At that time hellish spirits abounded. Disorderly
conditions prevailed. This is most clearly brought out in AC 5717 and 5718,
from which it is permissible to conclude that "viscid substances of the
brain" and "thick phlegm of the brain" refer to diseased conditions. It
is not so clear from AC 5386, but still, this number is in a series which
leads the thought towards hell. We conclude that phlegmy substances in
the brain are the direct opposite of "the brain is heaven," and of "the
better kind of lymph which is there" (AC 4049). The question that now arises
is, why did the Lord cause Swedenborg to observe phlegmy matters in the
brain so often, or at least to become so familiar with their occurrence?
Clearly because it was the last time of the Church, the state of which,
in the absence of love and charity, or at its end, is denoted by "the abomination
of desolation" (AC 2454:4, 3562). It appears that the Lord made use of
the unhealthy state of men's bodies so that through the anatomists we might
see representations of the abominable things that had to be overcome in
the world of mind and spirit. There was confusion among the anatomists
of the time because some of them seemed unable to distinguish between viscous
fluids which were normal (protoplasm for example) and those that were due
to disease (such as pituita or phlegm). At least this seems to be the cause
of the opinion that merely an excess of
&300. Perhaps the reader will enjoy this "discovery" in the order in which it occurred. The question arose in connection with the blood-brain barrier. This barrier is an important property of the circulatory system in the brain that we have as yet mentioned only in passing. Experiments show that large molecules do not pass out of the blood stream into the brain as readily as they do into other tissues. It seems that the lining of the capillaries is different. It is interesting to note that the other organ that has celestial associations as the brain has, namely the thymus gland (Chap X), also possesses a barrier to protect it from too free an influx of large molecules from the blood.
&301. In seeking for a correspondence of the
blood-brain barrier, one thinks at first of barriers in the Word, such
as cherubim, and especially the veil in the tabernacle, since this was
a barrier between the Holy and the Holy of Holies. However, we learn that
the correspondence of the blood-brain barrier is with the intermediate
angelic societies through whom communication is made; and their correspondence
in man is with "the cardiac and pulmonary plexuses" and with the medulla
oblongata, these being the means of communication between the heart and
lungs and between the cerebellum and cerebrum, respectively (AC 9670).
This would seem to make the veil a representative of communication rather
than of a barrier. Nevertheless upon the veil were cherubim, which signify
a guard, to prevent the mingling of spiritual and celestial goods; and
&302. When we look at the question of correspondences in a more general way, from a distance, as it were, we observe the head as the celestial, the body as the spiritual, and the feet as the natural. It is specifically stated (AC 9913:2) "that in general, the head corresponds to celestial things" (emphasis added), and consequently it is the neck "that by virtue of correspondences…signifies the influx, the communication, and the conjunction of celestial with spiritual things." Next we find, like the cherubim of the veil, a binding or boundary (AC 9914) which is required to be very strong (AC 9916). This was the binding round the opening of Aaron's robe which would rest upon the neck during wear. Therefore it has the same signification as the neck. It is emphasized (AC 9914) that "it is bounded and closed on all sides." These things describe the mode of influx of celestial into spiritual good, which is thus limited or bounded as the neck is strengthened by sinews and bones.
&303. It seems that we are, as yet, a long way from the blood-brain barrier, but these things provide a direction for our enquiries. In the first place, the strength and completeness of the limitation or binding is reminiscent of the physiological strength and completeness of the blood-brain barrier. We next realize that, if the outward flow of the celestial is to be so controlled, how much more must the reverse flow be kept in order, exactly as with the thymus. Now the reverse flow is extremely important. It is essential for continuing the life of the body; the blood supplies to the brain food, water, and oxygen, and removes carbon dioxide and other wastes. The barrier there presumably prevents the brain from being poisoned by many other substances that find their way into the blood (such as break-down products due to wear and tear of muscles, decomposition of food in the intestines, unwholesome substances in food, and so on). Can these things apply also to the Grand Man? We must first remember that there can be no influx of what is lower into what is higher, but there is reciprocal flow (DLW 410). Indeed, the nourishment of the brain by the blood, and the limiting of the exchange by the barrier in the brain, helps us to understand, to a slight degree, a process which could not be described to the apprehension when the Writings were given. Concerning this we read "let not any one wonder that the things which are here contained in the internal sense cannot be described to the apprehension, and that what are described transcend it" (AC 3085). We are now permitted to look at the process a little more closely.
&304. The transcendent operations we are now attempting to grasp are thus described: "there is a continual Divine influx through the internal man into the external, that is, an influx of celestial and spiritual things through the rational man into the natural, or, what is the same, into the natural things which are of the external man; and…by this influx, truths are continually called forth out of the natural man, elevated, and implanted in the good which is in the rational man" (AC 3085). This is similar to the activation of all parts of the body by the descent of commands from the brain through the nerves. These commands cause the body to eat, drink, and do many other things, by which a great variety of useful substances are procured or prepared and transferred to the blood stream, in which they are conveyed towards the brain. That is, they are "elevated." Now the blood-brain barrier comes into operation. It is a product of the brain corresponding to the celestial, as the binding round the neck of Aaron's robe represented a production by the celestial (AC 9915). As, in the body, the barrier prevents access to the brain by deleterious substances so, we deduce, the things that are "elevated and implanted in the good which is in the rational man" are strictly sorted, purified, and separated from the many harmful things that may be in the natural man. Thus the science of physiology now is such that by means of it we can apprehend the process of AC 3085. However, it still remains that we are seeing it only in a general way from correspondences, for "it is of such great wisdom because it is from the Divine" and "it can in no wise be explored as to a ten thousandth part of it."
&305. It would not be surprising to find such an important process described in other parts of the Writings. In DLW, we find, for example: "Out of these [star-like forms in the cineritious, i.e., grey matter] go forth fibres…into the body. These proceed to the ultimates of the body, and from ultimates return to their firsts. The return of fibres to their firsts is made through the blood vessels" (DLW 316). The first mental image this statement produces is of a fluid flowing through the nerves and returning via the blood stream, as though the nerves could feed their contents into the blood vessels. But this does not happen. Prior to Harvey (1578-1657) it was the authoritative view amongst anatomists that the arteries terminated in nerves. The capillaries were not seen until 1661. Even in those places where nerves have been shown to secrete substances into the blood, a general flow has not been found. In the case of the infundibulum and pituitary gland, only minute particles or droplets are transferred, and this is done in a controlled manner across barriers that prevent mixing, which would be chaotic and disorderly. The ultimates of the body to which the nerves descend are an expression of "thousands and myriads of forces [that], operating in act, appear as a one" (DLW 16) and the return to the firsts in the brain is quite different in character from that which was sent out as a cause. This return is far more wonderful than a mere return flow (such as that of electricity along the neutral wire). The return that is made through the blood consists in chemical activation, protection, nourishment, and cleansing. These take place when the nerves, activated by the brain, stimulate the body to its normal healthy functions. It is easy to see how this corresponds to the "progression of love though wisdom into uses," or ultimates, and to the return "out of these, by means of the enjoyment of uses…to their firsts." That is to say, there is a return of uses to the brain in the form of various chemical and physical services. This physiological circle of flow and return is particularly instructive as an example of correspondences, for we have here a process in brain and body corresponding to mental processes that we can observe by introspection. These are also outlined in DLW 316.
&306. The circle that has just been discussed is put forward in DLW as an image of creation. There is also another path of return to the brain and that is via the nerves connecting the various sense organs to the brain. This opens a vast new field of correspondences into which we will not now enter except to say that it forms part of a circle that is quite different. Although the nerves of the senses are connected to the brain, they conduct only information to it. They provide no material sustenance. They are, as it were, in a discretely different degree. Dealing with information only, they seem to be a step nearer the spiritual, though still actually material. It is almost as though they do not quite descend to the ultimates in the sense of food, drink, and cleansing. We must not, however, imagine either creation or the body to be as simple as two circles. There is yet another return via the blood that would appear also to be an image of creation. For there are nerves from the brain that go only to the pituitary gland. They secrete hormones into the blood and thereby exert profound effects upon the body, as will be seen in the chapter following.
&307. The circles comprising outflow from the brain and return via the blood are, as we have said, images of creation. From these circles, it is clear that the return is in an altogether different form from the outflow. As a created subject, man receives life from the Lord, and makes a return to the Lord whenever he engages in some use (from love, charity, obedience, fear, etc.), but it is not a return of life. Life flows out from the Lord and ultimates are created. They produce returns in great variety, whereby heaven is nourished.
15 The cerebrospinal fluid bathes the whole outer surface of the brain and spinal cord and fills all the cavities (i.e., ventricles) inside the brain. It is produced almost (or perhaps quite) entirely by the choroid plexuses. These are frilly types of structure inside the ventricles and they seem to have no other purpose than the production of cerebrospinal fluid. The fluid itself has its own characteristic composition by which it is easily distinguished from serum and lymph.
16 In The Cerebrum (See Footnote 18 in No. 312), Swedenborg described Pacchioni's findings (Swedenborg, 1938). His sketch is reproduced in the companion volume of anatomical plates. From Nos. 232d and 232e of The Cerebrum, it is clear that Pacchioni observed the connections between the granulations and the pia mater, but he seems to have been alone in this. The granulations were thought to be glands.
17 It was thought at one time that the spaces between the cells of the brain were too small to allow diffusion to be significant. This opinion arose when studies of fine structure, as opposed to ordinary microscopic observations, were made. It has since been shown that when the tissues are deprived of oxygen in the course of ordinary methods of preparation, most of the intercellular fluid is absorbed by the cells themselves which therefore expand into all the available space. It is now thought that this space is much more than the early estimate of five percent of the total volume and nearer the still earlier figure of twenty percent. With spaces like this, diffusion is likely to be important if the fluids are not identical.