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Indeed, the associations between the skin and the brain are extremely inti-"'.
mate. This fact is the basis of the "lie detector test"; specific mental states directly
influence the electrical properties of the skin, and in reguLfi ways that can readily
be measured and correlated. And from blushing to hives, from goose bumps
to shingles, the skin demonstrates a reflex expressiveness to scores of mental
events.
1\
The Ectoderm
This close association between the skin and the central nervous system could
not have more concrete anatomical and physiological connections. All tissues
and organs of the body develop from three primitive layers of cells that make
up the early embryo: The endoderm produces the internal organs, the mesoderm
produces the connective tissues, the bones, and the skeletal muscles, while the
ectoderm produces both the skin and the nervous system.
Skin and brain develop from exactly the same primitive cells. Depending upon
how you look at it, the skin is the outer surface of the brain, or the brain is the
deepest layer of the skin. Surface and innermost core spring from the same ,­
mother tissue, and throughout the life of the organism they function as a single
unit, divisible only by dissection or analytical abstraction. Every touch initiates
1
ECTODERM
Fig. 2-15: The emergence of the three primitive germ layers - the ectoderm, the mesoderm, and the endoderm.
The ectoderm gives rise to the nervous system and the skin, the mesoderm to the muscles and connective tissues,
and the endoderm to the internal organs.
;
36
JOB'S BODY
a variety of mental responses, and no­
where along the line can I draw a sharp
Neun1 groove distinction betWeen a periphery which
Notochordal
~--t-I-- plate
purely responds as opposed to a central
"'-'III;;;IT- fntra·embrto nic
nervous system which purely thinks. mesoderm
Head process
My tactile experience is just as central .nO
to my thought processes ~ are lan­
canal
guage
skills or categories of logic.
Amnion
Between the third and fourth week
Primitlve node with opening of of
the embryo'S life, the ectoderm
amnio-enteric cana' begins to differentiate into skin tissues
and neural tissues. The skin layer sepa­
Yolk sac
mesode ... m
rates from the central neural tube and
Primitive strea){
and groove
migrates outward, as the developing
Ectoderm
muscles, bones and organs push it far­
ther and farther away from the core.
Fig. 2-16: The three germ layers in an 18-day-01d
However, this is far from the end of
embryo.
the close chemical, structural, and
functional affinities between the skin and the brain. In spite of the increasing
distance that separates them, properties of the skin continue to playa material
role in the development and organization of the central nervous system.
amnio~ente..-ic
L
~
;.,.,..-----~
..
lacuna in
Dilated gland
Mouth of
dilated gland
syn_cytiotrophoblilst Slnu:!.oid
Coa.gulum
Entoderm
Amnion
Primary
york sac
Sinusoid
Ectoderm
lacuna in
syncytiotrophoblast
Primary
Uterine
mesoderm epithelium
Fig. 2-T7: A drawing of a lz-day-old embryo, ~howing the three primitive germ layers.
..
SKIN
no-
37
Neural Mapping
In order to accurately locate any stimulus on the body's surface, the brain
relies upon a precise spatial arrangement of its circuitry, such that specific adja­
cent nerve endings on the skin transmit their signals through parallel neurons
which terminate in specific adjacent cell bodies in the sensory cortex. The princi­
ple involved is like that used in modern fiber optics: If the glass fibers at the
observer's end of the bundle are arranged as they are at the far end, he will
receive a clear, unscrambled image of any object to,,:,{ard which the far end is
~~~
Weok
stimulus
-
Model'llle stimulus Slronq
stimulus
Fig. 2-18: An area of skin, innervated by endings from several axons. The axons are gathered together into a
nerve trunk, where they preserve their parallel arrangements throughout their full length. Thus, when three
separate but simultaneous pin-pricks touch the skin, the. spatial relationship of the stimulated axODS in the
trunk correspond to the arrangement of the pin-pricks on the surface of the skin. The principle is similar to fiber
optics.
The spatial relationships of the various parts of the periphery are, then, pro­
jected by their parallel nerve fibers and "mapped" onto corresponding areas ofthe
cortex, where they are arranged as the familiar sensory homunculus. It is in this
way that the brain separates functions and pinpoints locations throughout the
body.
For instance, in the dorsal column of the spinal cord (where all the sensory
tracts are bundled together), the sensory fibers from the feet lie closest to the
midline, and as we rise up the body and up the column, successively added
sensory trunks add their fibers progressively toward the lateral sides of the dorsal
column.
This spatial organization is main­
tained with precision throughout the
sensory pathway all the way to the
somesthetic cortex. Likewise, the
fiber tracts within the brain and those
extending into motor nerves are spa­
tially oriented in the same way. 18
Fig, 2-19: The sensory cortex straddles the midsec­
tion of the upper surface of the brain.
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40
JOB'S BODY
This same principle of parallel fiber arrangement produces a similar homun­
culus upon the motor cortex, and another upon the cortex of the cerebellum.
These minianue maps of the body correspond not only to the peripheral ar­
rangement, but also to one another, so that parallel circuits not oniy link my
actual hand to my sensory cortex "hand"; they also link this sensory "hand"
t9 my motor cortex "hand" and to my cerebellar "hand" as well. EaclNnap
'corresponds point for point to all the others, and all are linked together by
'--parallel circuits.
At one time it was suggested by neural anatomists that such parallel pathways
developed in the embryo before being assign~d to any specific functions, and
that particular channels were later created by habitual usage, much like water
wears a channel for a stream bed. Conflicting or extraneous paths would be
eliminated by atrophy, and new channels could be re-routed in case of damage.
Later it was postulated that these parallel circuits were established genetically
in the developing brain and spinal cord, which then reached out from the central
core with axons and nerve ends to contact the periphery. It was not clear just
how the nerve ends knew exactly where to go; perhaps there was a good deal
of randomness to their branching which the organism later sorted out by means
of trial and error.
More recently, it seems that neither of these earlier views may be the case.
It~now appears that the organization of this parallel circuitry is actually initi­
aQ at the periphery. Local qualities in the skin, the joints, and the deep tissues
"tag" the nerve ends which contact them with subtle chemical messages, and
these chemical "tags" direct axons growing inward toward the appropriate con­
nections in the spinal cord and brain. The process is anything but random or
'~'" trial and error. It is highly specific, and it is the periphery which helps to organize
the connections in the central nervous system, not an organized central nervous
system which reaches out to innervate the periphery.
,,' This more recent view that it is peripheral conditions which organize the
'>~actual development of neural circuits and guide the process of mapping is of
// central importance to bodywork. It suggests that the use of touch and sensation
to modify our experience of peripheral conditions exerts an active influence
upon the organization of reflexes and body image deep within the central nerv­
ous system. Such a view seems to be borne out by the following kinds of experi­
ments.
If a patch of skin from the belly of a frog embryo is exchanged with a patch
from his back, and the two patches are allowed to re-attach in their new locations
and regenerate their nerve ends, a very curious thing happens. When I tickle the
patch on the frog's belly, he rubs his back, and when I tickle the one on his
back, he rubs his belly. In spite of the fact that the major sensory nerve trunks
deep to the skin have not been disturbed, the frog confuses front and back when
his transposed patches are stimulated. Nerve ends in the skin taken from the
belly still somehow manage to excite the "belly" areas in the frog's sensory
and motor cortexes, even though the signals must now go through circuits
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SKIN
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associated with the back. The neural
connections in the brain have some­
how shifted to accommodate the
shifted ~reas of skin. These transplants
can be repeated with many variations,
involving various muscle sets, entire
limbs and even the eyes. In every in­
stance, their results are similar­
stimulation of transplanted tissue re­
sults in reactions that would be appro­
priate if the tissue were still atits origi­
nal site, and not at the ~ new one.
"It is necessary to conchicte," says R.
W. Sperry, the author of a senes of
these experiments,
that the sensory fibers that made con­
nections with the grafted tissues must
have been modified by the character
of these tissues. . . . Growing freely
into the nearest areas not yet in­
nervated the fibers established their
peripheral terminals at random.
Thereafter they must proceed to form
41
t To granule layer
leading process
of neuron
Process of
radial glial cell
T railing process
of neuron
t
From external
granule layer
Fig. 2-22: The growing sensory axon in the foetus
follows the lead of a glial cell-its supportive and
nutritive partner. Presumably, the glial cell carries
chemical messengers from the skin which are
matched against chemical tags al each ascending
level up the spinal column and the brain, identifying
the appropriate internal cOllnections. Each axon is
then chemically coded to follow its particular glial
cell.
Fig. 2-23: An axon following its glial partner as they grow. Tbe nerve cell's nucleus is tbe large dark oblong
shape. The glial cell is tbe grey band running from corner to corner diagonally, and the nerve's growing axon is
next to it.