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Nerve fiber components of communicating rami and sympathetic roots in man.

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NERVE F I B E R COMPONENTS O F CO&IMUNICATING
RAM1 AND SYMPATHETIC ROOTS I N MAN'
ALBERT KUNTZ, HENRY HARLAND HOFFMAN AND
MERLE WILLIAM JACOBS a
Department of Anatomy, St. Lozeis University School o f Medicine
St. Louis. Missouri
T W O *FIGURES
The sympathetic preganglionic nerve fibers emerge from
the spinal cord in the ventral roots of the thoracic and the
rostra1 two or three lumbar spinal nerves. They join the
sympathetic trunk through the communicating rami, which
also convey afferent nerve fibers. The communicating (white)
rami, consequently, are made up of preganglionic and visceral
afferent fibers. The sympathetic postganglionic fibers join
the spinal nerves through the sympathetic roots (gray communicating rami) which are made up chiefly of postganglionic
fibers, but also convey some afferent ones. Most of the
postganglionic fibers are unmyelinated. Most of the afferent
fibers in the sympathetic roots are myelinated. Following
degeneration of the afferent and any preganglionic fibers that
may traverse a sympathetic root, in experimental animals
(cats), some myelinated fibers in it remain intact (Ranson and
Billingsley, '18 ; Kuntz and Farnsworth, '31). These appear
to be myelinated postganglionic fibers. The abundance and the
variability in the numbers of myelinated fibers in sympathetic
roots in man (Pick and Sheehan, '46) favors the assumption
that not all of them fall into the categories of afferent and
preganglionic fibers.
Supported by USPHS Grant B-666.
1955.
* USPHS Fellow, Summer
29
30
KUNTZ, HOFFMAN A N D J A C O B S
MATERIAL AND METHODS
The relationships of communicating rami and sympathetic
roots were studied in a series of dissections of the sympathetic
trunks and their connections with the spinal nerves in man.
Dorsal and ventral nerve roots, communicating rami and
sympathetic roots were sectioned transversely and stained
with Sudan black. Communicating rami and sympathetic roots
obtained at autopsy were stained with osmic acid and sectioned
transversely. Caliber measurements and counts of myelinated
fibers were carried out in both Sudan black arid osmic acid
preparations. The occurrence and the distribution of accessory
ganglia located in relation to communicating rami and sympathetic roots was studied in serial longitudinal sections of
these structures arid adjacent portions of the spinal nerves
stained with hematoxylin and eosin.
I n order to isolate in sympathetic roots myelinated fibers
that are neither afferent nor preganglionic, cats and dogs were
subjected to operative procedures in which afferent and
preganglionic fibers were severed. After allowing ample time
for degeneration of the interrupted fibers, communicating
rami and sympathetic roots were stained with osmic acid and
sectioned transversely. Caliber measurements and counts
of the myelinated fibers in these sections were carried out.
ANATOMICAL DATA
Veatrnl roots. Throughout the sympathetic outflow every
ventral spinal nerve root conveys preganglionic fibers that
reach the sympathetic trunk through a communicating ramus.
I n general, preganglionic fibers fall within the diameter range
of less than 1 to 3.5 H. In the ventral nerve roots that convey
preganglionic fibers most of the fibers within this diameter
range are arranged in relatively dense aggregates that are
surrounded by larger, less closely aggregated fibers (fig. 1A).
These aggregates of small fibers occur throughout the entire
transverse section of the ventral root (fig. IB). Coinparable
fiber aggregates do not occur in the ventral roots of the spinal
SYMPATHETIC RAM1 AND ROOTS
31
nerves rostral to the 8th cervical. Actual counts of the total
number of aggregated fibers in a ventral nerve root and the
fibers in the diameter range of preganglionic fibers in the
communicating ramus arising from the same nerve indicate a
relatively close correspondence. It appears highly probable,
therefore, that the preganglionic fibers traverse the ventral
nerve roots chiefly in these aggregates of small fibers.
Communicating rami. The communicating rami (white)
are made up predominantly of preganglionic fibers all of
which appear to be myelinated (fig. 1C). They also include
afferent fibers many of which are myelinated and larger than
the preganglionic fibers. Most communicating rami are separate from the sympathetic roots (gray communicating rami),
but in some instances preganglionic and postganglionic fibers
are conveyed in the same ramus. Usually a communicating
ramus joins a single sympathetic trunk ganglion, but in some
instances it divides into two or more branches that join the
same sympathetic trunk ganglion or adjacent ones. The
numbers of preganglionic and afferent fibers in different
communicating rami vary within a relatively wide range.
I n the presence of accessory ganglia in the ventral primary
ramus of a spinal nerve or adjacent to it, some preganglionic
fibers make synaptic connections in these ganglia through
either collateral or terminal branches. The total number of
preganglionic fibers in a communicating ramus, therefore, need
not equal the total number in the corresponding ventral
nerve root. Our observations relative t o accessory ganglia
located in relation to ventral primary and communicating rami
support the assumption that they occur most frequently in
the rostral two or three thoracic segments and from the
11th thoracic to the 3rd lumbar segment. Except in segments
in which accessory ganglia occur in relation to the ventral
primary or the communicating ramus, all the preganglionic
fibers that emerge in a given ventral nerve root throughout
the sympathetic outflow probably join the sympathetic trunk.
Sympathetic roots. The sympathetic roots are made up
predominantly of postganglionic fibers, most of which are
Fig. 1 Photoniicrograplis from sections of ventral nerve root, a communicating
ramus and sympathetic roots in man stained with Sudan black. A. Area of a
section of the ventral root of the 4th thoracic nerve showing a n aggregate of
small myelinated fibers surrounded b y larger myelinated fibers. B. Lower
magnification of the same section showing the distribution of aggregates of
small myelinated fibers. C. Section of the communicating ramus of the 9th
thoracic nerve showing predominance of myelinated fibers. D. Section of the
sympathetic root of a 5 t h thoracic nerve showing relatively few mgelinated
fibers. E. Section of the sympathetic root of a n 8th thoracic nerve showing
greater abundance of myelinated fibers. F. Section of the sympathetic root of
a 9th thoracic nerve showing still greater abundance of myelinated fibers.
33
SYMPATHETIC RAM1 AND ROOTS
33
unmyelinated, but they include variable numbers of myelinated
fibers interspersed among the unmyelinated ones (fig. lD, E,
F). The sympathetic root in a given segment may consist of
a single ramus or of two or more lesser rami. Sympathetic
roots can be classified, as has been done by Pick and Sheehan
('46), according to the abundance of myelinated fibers in
them. Most of the myelinated fibers fall within the diameter
range of preganglionic fibers, but many are too large to be
included in this category. Most of the larger fibers fall
within the diameter range of 3.5 to 15 p. Myelinated fibers
that exceed 3 . 5 ~in diameter are more abundant in the
sympathetic roots of the nerves that contribute to the brachial
and lumbosacral plexus than in those of the intervening
thoracic nerves. Those of some of the thoracic nerves include
relatively few larger fibers (fig. lE, F).
Accessory ganglia are known to occur frequently in relation
to sympathetic roots as well as in relation to ventral primary
and communicating rami. Our data relative to accessory
sympathetic ganglia in man, like those of other investigators
(Rossi, '31 ; Gruss, '32 ; Skoog, '47 ; Wrete, '35, '51), support
the assumption that they occur more frequently in the cervical
and rostral two or three thoracic segments and in the caudal
thoracic and lumbar segments than in the intervening ones.
Accessory ganglia in the cervical region usually are located
in relation to sympathetic roots. Many of those in the lumbar
and sacral segments likewise are related to sympathetic roots.
Others throughout the thoracic, lumbar and sacral segments
are located in relation to ventral primary and communicating
rami.
Histological examination of serial longitudinal sections of
sympathetic roots in 5 human cadavers has revealed accessory
ganglion cells frequently in those of the nerves that make up
the brachial and lumbosacral plexuses, less frequently in those
of the more rostral cervical nerves and occasionally in those
of thoracic nerves. Ganglion cells in sympathetic roots or
adjacent to them occur in small and larger aggregates. Most
of them are incorporated in compact ganglia. Actual counts
34
KUNTZ, KOFFMAN AND JACOBS
of the ganglion cells in a limited number of accessory ganglia
located in sympathetic roots or in relation t o them indicate
a range of 10 to over 2000. Ganglia that comprise 100 to 250
ganglion cells were observed frequently. Many of the sympathetic roots examined revealed no ganglion cells.
Most preganglionic fibers that make synaptic connections
with accessory ganglion cells that are located in relation to
sympathetic roots undoubtedly traverse these roots to the
points at which the ganglion cells are located. I n some
sympathetic roots such synaptic relationships are sufficiently
numerous to account for large numbers of preganglionic fibers.
I n sympathetic roots that include accessory ganglia, many
of the myelinated fibers that do not exceed 3.5 p in diameter
undoubtedly are preganglionic. Myelinated fibers within the
preganglionic caliber range, however, occur in many sympathetic roots in the absence of accessory ganglion cells
related to them.
I n order to obtain data relative to the anatomical relationships of all the myelinated fibers, osmic acid preparations of
sympathetic roots of cats and dogs were obtained following
degeneration of the afferent and the preganglionic fibers in
the nerves in question. The experimental animals were subjected to surgical procedures in which a series of spinal nerve
roots was sectioned unilaterally distal to the spinal ganglia
but proximal t o the sympathetic roots and communicating
rami or the sympathetic trunk was divided caudal to the
sympathetic preganglionic outflow. These procedures insure
degeneration of both afferent and preganglionic fibers in t,he
sympathetic roots affected. Osmic acid preparations of sympathetic roots in which the afferent and the preganglionic
fibers had undergone degeneration, obtained from cats, exhibit
many intact myelinated fibers. As compared with sections
of the contralateral normal sympathetic roots, the myelinated
fibers are reduced in numbers and most of those that remain
intact do not exceed 2 p in diameter (fig. 2A, B). Counts
of the intact myelinated fibers in sections of the sympathetic
roots of the 6th and 7th lumbar and the 1st sacral nerves
S Y M P A T H E T I C RAM1 A N D ROOTS
35
of a cat following degeneration of the fibers interrupted by
section of the left sympathetic trunk just rostra1 to the 6th
lumbar segment and between the 6th and 7th lumbar nerves
a r e recorded in table 1.
Fig. 2 A. Section of the sympathetic root of the right 7th lumbar nerve
of a cat, stained with osmic acid, showing normal frequency of myelinated
fibers. B. Section of the sympathetic root of the left 7th lumbar nerve of the
same cat after degeneration of the preganglionic and the afferent fibers, stained
with osmic acid, showing myelinated fibers t h a t remain intact. C . Section showing
a slender ramus derived from the sympathetic trunk in man adjacent t o
intercostal blood vessels. The ramus includes accessory ganglion cells.
36
IIUNTZ, HOFFMAN AND JACOBS
Since the left sympathetic trunk was divided caudal to the
sympathetic preganglionic outflow, both the afferent and
the preganglionic fibers in the left sympathetic roots in
question were interrupted and underwent degeneration. The
myelinated fibers that remained intact in these roots, consequently, must be postganglionic. The demonstration by
Ranson and Billingsley ( '18) of myelinated postganglionic
fibers in the cat, therefore, is confirmed.
Osmic acid preparations of normal sympathetic roots of
dogs in general exhibit fewer myelinated fibers than those
of cats. Following degeneration of both the afferent and the
preganglionic fibers, most sympathetic roots of the dog exhibit no intact myelinated fibers. On the basis of these obswTABLE I
SYMPATHETIC
ROOT
6th lumbar
7th lumbar
1st sacral
NUMBER O F MYELIBATED FIBERS
Rieht
Left
234
305
118
145
159
63
vations it may be assumed that myelinated postganglionic
fibers occur only rarely, if at all, in the sympathetic roots
in the dog.
Sections of human sympathetic roots exhibit myelinated
fibers in greater abundance than sections of those of the dog.
With respect to the abundance of myelinated fibers the sympathetic roots of man resemble more closely those of the cat
than those of the dog. A relatively high percentage of the
myelinated fibers in human sympathetic roots falls within
the diameter range of those that remain intact in the sympathetic roots of the cat after degeneration of the afferent
and the preganglionic fibers. Counts of the myelinated fibers
in three size categories are recorded in table 2.
These counts cannot be regarded as highly accurate, but
they reflect the variations in the total number of myelinated
fibers and in the numbers of those in each of the several
37
SYMPATEETIC RAM1 A N D ROOTS
size categories in different sympathetic roots. I n most of the
sympathetic roots 50% or more of the myelinated fibers do
not exceed 2 . 5 ~in diameter. They fall within the diameter
range of most of the myelinated fibers in sympathetic roots
of the cat that remain intact following degeneration of the
preganglionic and the afferent fibers. Total numbers of
myelinated fibers in the sympathetic roots vary w-ith the
total numbers of both myelinated and unmyelinated ones.
The total number of fibers in a given sympathetic root is
correlated with the extent of the vascular bed and other
autonomic effector organs that are innervated through that
root.
Segnzemtal sympathetic rami. I n addition to the sympathetic roots and the splanchnic nerves the sympathetic
trunk gives off more slender rami that neither join the
spinal nerves nor extend t o the thoracic or abdominal viscera.
In the cervical and rostra1 thoracic segments some of these
rami join the plexuses on the carotid and the vertebral
arteries. In the thoracic and lumbar segments such rami in
general extend along the segmental blood vessels and contribute to their innervation. Some segments include more
than a single ramus of this kind. Frequently, two or more
slender rami may be traced from a segment of the sympathetic
trunk along the segmental vessels.
DIAMETER
OF FIBERS
__-C6
C7
Less than
2.5 microns
45 1443
2.5 t o 3.5
iiiierons
93
Over 3.5
inicroiis
632
108 145T
R W N E N T A L DESIGNATION
C8
TI
T3
T4
T5
T6
T7 TK
TY
L1
L2
L3
L4
L5
735 1747
62 135 185 113 424 435 403 1104 511
579 1932
630
265
697
68
71
57
33 128 130
83
293 244
235
574
220
679 1132
83
93
69
57 161 136 340
258 167
338
746
164
246 3532 1679 3576 213 299 311 203 713 701 626 1655 922 1152 3352 1014
38
KUNTZ, HOFFMAN A N D JACOBS
The fiber composition of these slender rami is comparable
to that of the sympathetic roots. Some of them also include
ganglion cells in small numbers (fig. 2C). Most of the unmyelinated fibers undoubtedly are postganglionic and arise
in sympathetic trunk ganglia. The larger myelinated fibers
and some of the smaller ones probably are afferent. Rami in
which ganglion cells are located must also include some preganglionic fibers.
DISCUSSION
The assumption that the white communicatiiig rami are
made up predominantly of myelinated fibers is supported by
the data obtained from both animal and human preparations,
but they also include unmyelinated fibers. The sympathetic
roots (gray communicating rami) are separate from communicating rami in most instances, but frequently at least a
portion of the sympathetic root fibers and fibers of the
communicating ramus traverse a common nerve bundle. I n
man, as observed by Pick and Sheehan ( '46), the sympathetic
roots vary widely with respect to the abundance of myelinated
fibers that traverse them, but all include both small and
larger ones. The finding of Ranson and Billingsley ( '18) that
the sympathetic roots in the cat include myelinated postganglionic fibers is confirmed. I n view of the occurrence in the
sympathetic roots in man of large numbers of myelinated
fibers in the diameter range of those that remain intact in
the sympathetic roots of the cat after degeneration of the
preganglionic and the afferent fibers it appears probable that
many postganglionic fibers in the sympathetic roots in man
are myelinated. The assumption that the small myelinated
fibers in human sympathetic roots are exclusively postganglionic is unwarranted, however, since some afferent fibers in
these roots probably are smaller than some efferent ones.
The larger myelinated fibers in the sympathetic roots in man
undoubtedly are afferent. The afferent component probably
also includes some small myelinated and some unmyelinated
fibers. The occurrence of afferent fibers in sympathetic roots
SYMPATHETIC RAM1 AND ROOTS
39
in animals has been amply demonstrated both anatomically
(Kuntz and Farnsworth, '31) and physiologically (Threadgill
and Solnitzky, '49). The assumption that some afferent
conduction from the extremities is mediated through dorsal
root fibers that traverse sympathetic roots and the sympathetic
trunk is also supported by clinical experimental data (Walker
and Nulsen, '48; Echlin, '49; Sweet and White, '53). Afferent
conduction from trunk dermatomes through the sympathetic
trunk has also been demonstrated (Van Harreveld and Smith,
'53).
On the basis of the available experimental data and the
anatomical data obtained in the present study it appears
highly probable that all sympathetic roots in man are traversed by afferent nerve fibers. On the basis of the fiber counts
recorded in table 2 it is apparent that the sympathetic roots of
the nerves that make up the brachial and the lumbosacral
plexuses are traversed by myelinated fibers over 2.5 I-( in diameter in much larger numbers than those of the thoracic nerves
caudal to the second. On the assumption that these fibers are
predominantly afferent it is apparent that afferent fibers are
distributed through sympathetic roots in greater abundance
to the extremities than to trunk segments. The afferent fibers
that traverse sympathetic roots probably are distributed
chiefly to blood vessels. The total number of afferent fibers
that traverse a given sympathetic root, like the total number
of its efferent fibers, appears to be correlated with the extent
of the vascular bed that is innervated through that root.
It need not be assumed, however, that all the fibers concerned
with the afferent innervation of the peripheral blood vessels
and other peripheral autonomic effector organs traverse
sympathetic roots.
The frequent occurrence of accessory ganglion cells in
sympathetic roots or in close proximity to them affords an
explanation of the occurrence of preganglionic fibers in some
sympathetic roots. The ganglion cells in question probably
represent cells that have been displaced from the primordia
of sympathetic trunk ganglia, and the preganglionic fibers to
40
KUNTZ, HOFFMAN AND JACOBS
which they are synaptically related extend beyond the sympathetic trunk in the sympathetic roots. Only a small percentage of the myelinated fibers in synpathetic roots can
be accounted for on this basis. Most of the preganglionic fibers
that make synaptic connections with ganglion cells that are
located in proximity to segmental blood vessels probably do
not traverse sympathetic roots, but reach the cells in question
through segmental rami from the sympathetic trunk.
On the basis of all the available data, the sympathetic
roots in man, like those in the cat, appear to be made up
predominantly of postganglionic fibers most of which are
unmyelinated. They are traversed by dorsal root fibers most
of which probably are distributed to peripheral blood vessels.
Some are also traversed by limited numbers of preganglionic
fibers.
SUMMARY
The sympathetic preganglionic nerve fibers traverse the
ventral nerve roots in dense aggregates of small myelinated
fibers. The communicating rami are made up predominantly
of myelinated fibers. Those that are larger than the preganglionic fibers are afferent. The afferent component also
includes fibers that fall within the preganglionic caliber
range.
The sympathetic roots include myelinated fibers interspersed among the unmyelinated ones. The myelinated fibers
that exceed 3.5 p in diameter and some smaller ones are afferent. All sympathetic roots in man probably are traversed by
afferent fibers most of which are distributed to peripheral
blood vessels. Sympathetic roots with which accessory ganglion cells are associated also include preganglionic fibers. The
total number of afferent fibers in a given sympathetic root
appears to be correlated with the extent of the vascular
bed that is innervated through that root.
In the cat many small myelinated fibers remain intact in
sympathetic roots following degeneration of both the afferent
and the preganglionic fibers. They are regarded as myelinated
SYMPATHETIC RAM1 AND ROOTS
41
postganglionic fibers. A relatively high percentage of the
myelinated fibers in human sympathetic roots falls within the
caliber range of those that remain intact in sympathetic
roots of the cat following degeneration of the afferent and
the preganglionic fibers. It appears highly probable, therefore, that the sympathetic roots in man also include myelinated
postganglionic fibers.
LITERATURE CITED
ECHLIN,F. 1949 Pain responses on stimulation of the lumbar sympathetic
chain under local anesthesia-A
case report. J. Teurosurg., 6:
530-533.
GRUSS, W. 1932 Ueber Ganglien in Ramus Communicans. Z. Anat. u. Entwg.,
9’7: 464-471.
1931 Distribution of afferent fibers via the
KUNTZ,A., AND D. I. FARNSWORTH
sympathetic trunks and gray communicating rami to the brachial
and lumbosacral plexuses. J. Conip. Neur., 5 8 : 389-399.
PICK,
J., AND D. SHEEHAN1946 Sympathetic rami in man. J . Anat., 80: 12-20.
ROW, F. 1931 Neue Befunde iiber die Entwicklung des Sympathicus. Verh.
Anat. Ges. Jena., 40: 89-94.
SKOOG,T. 1947 Ganglia in the communicating rami of the cervical sympathetic
trunk. Lancet, 2: 457-460.
SWEET, W. H., AND J. C. WHITE 1953 Disposition of pain fibers in some of
the sympathetic nerves in man. Trans. Am. Neurol. Assoc., 78:
131-1 36.
1949 Anatomical studies of affereiicy
THREADGILL,
F. D., AND 0. SOLNITZKY
within the lumbosacral sympathetic ganglia. Anat. Rec., lQ3 : 96.
VAN HARREVELD,
A., AND H. N. SMITH 1953 On a “sympathetic” component
of the afferent innervation of trunk dermatomes. J. Neurophysiol.,
15: 313-318.
WALKER,E. A., AND F. NULSEN1948 Electrical stimulation of the upper
thoracic portion of the sympathetic chain in man. Arch. Neurol.
and Psychiat., 59: 559-560.
WRETE,M. 1935 Die Entwickelung der intermediiiren Ganglien beim Menschen.
Gegenbauer ’s Morph. Jahrb., 7’5 : 229-268.
1951 Ganglia of rami communicantes in man and mammals particularly monkey. Acta Anat., I S : 229-236.
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