Copyright
E. A. (Edward Albert) Sharpey-Schäfer.

Text-book of physiology; (Volume v.1) online

. (page 69 of 147)
Online LibraryE. A. (Edward Albert) Sharpey-SchäferText-book of physiology; (Volume v.1) → online text (page 69 of 147)
Font size
QR-code for this ebook


lingual branch of the third division of the fifth nerve. The nerve thus
formed may be called the cliordo-lingual ; it extends roughly up to the
dorsal edge of the sublingual gland ; here nearly all the fibres for the
submaxillary gland, and about half of those for the sublingual gland,
leave the lingual fibres, generally in four or five delicate strands, lying
close together. These strands, with the tissue around them, are easily
dissected out as a single bundle, and the bundle of nerve strands is
called the chorda tympani, although it is a part only of the chorda
tympani proper. The chorda tympani curves backwards towards the



48o THE SALIVAR Y GLANDS.

gland ducts, and accompanies them into the glands. Other fine
filaments, coming from the chorda tjmpani proper, are given off' from
both sides of the lingual, as it runs forward over the sublingual
gland ; most of these end in this gland, but a few fibres, varying in
number in different animals, run back and supply the submaxillary
gland. Finally, a few fibres, from the chorda tympani proper, con-
tinue their course in the lingual, and supply the glands and blood
vessels in the area of distribution of the lingual nerve in the tongue.

On the course of the nerve filaments to the glands are a number
of small and often microscopic ganglia. In the smaller filaments these
begin a very short distance from the lingual nerve, and then occur at
intervals as far as the terminations of the ducts. Fibres from the
filaments and ganglia intermingle, and form a plexus ; this plexus, at
first, overlies the sublingual gland, but, further on, surrounds and
accompanies the ducts, chiefly those of the sublingual gland. The
larger part of the chorda tympani passes by this plexus, and runs
direct to a ganglion in the hilus of the submaxillary gland ; where the
duct begins to divide, this ganglion gives off strands, which form
another plexus, surrounding and accompanying the divisions of Whar-
ton's duct.

vSome of the ganglia in the plexus over the sublingual gland are
relatively large ; thus in the dog there is, as a rule, a ganglion, which
may be seen with the eye, in the angle between the lingual and
the chorda tympani. This was called, l^y Bernard, the submaxillary
ganglion ; as we shall see presently, it is more appropriate to call it
the sublingual ganglion. Another, and a larger ganglion, is that
spoken of above, as present in the submaxillary gland. As this belongs
chiefly, if not entirely, to the submaxillary gland, we may call it the
submaxillary ganglion. But it must be remembered that the nerve-
cells which occur on the course of the chorda tympani fibres, either to
the sublingual or to the submaxillary gland, are not collected together
in a single ganglion, but occur scattered at intervals on the nerve-
plexus into which the fibres run.

The nerve-cells are on the course, both of the secretory and of tlie
vaso-dilator fibres of the chorda tympani. This may be shown by
stimulating the chorda tympani, centrally of the nerve-cells, and
peripherally of them, before and after injecting nicotine into a vein.^
The experiment is best made in a cat. Normally, stimulation of the
chorda tympani, in any part of its course, causes a flow of saliva, and an
increased blood flow from the gland vein. After injecting a small dose
of nicotine into a vein (cf. p. 515), stimulation of the chorda tympani in
the tympanic cavity, or of the chordo-lingual nerve, has no effect. But
a rapid secretion, and a greatly increased blood flow from the gland vein
— in fact, the usual effects of stimulating the chorda tympani — are
readily obtained by stimulating the nerve plexus in the hilus of the
gland. Since no nerve except the chorda tympani is able to produce
these effects, we may safely conclude that, in stimulating the nerve-
plexus in the hilus of the gland, it is the peripheral chorda tympani
fibres which cause the secretion and increased blood flow. The amount
of nicotine given does not prevent — nor, so far as we know, affect — the
passage of a nervous impulse along a nerve-fibre, and, in consequence,
we conclude that the nerve-cells are on the course of the chorda

^ Langley, Journ. Physiol., Cambridge and London, 1890, vol. xi. p. 123.



THE CHORDA TYMPANI AND NERVE-CELLS. 481

tympani fibres, and that nicotine either acts on the connection of the
nerve-fibres with the nerve-cells, so that a nervous impulse cannot pass
from one to the other, or acts on and paralyses the cells. The former is
the more likely, and, in accordance with what is known generally
regarding the relations of different nerve units, we may suppose that
the nerve-fibres divide into fibrils, which terminate on the nerve-cells,
and that these terminations are paralysed by nicotine.

I have only spoken, so far, of the effect, after nicotine injection, of
stimulating the chordo -lingual and the plexus in the hilus of the gland.
If the stimulus be applied between these two places, the effect varies in
different cases, and varies also in different animals. Broadly speaking,
as the electrodes are passed along the chorda tympani and nerve-
plexus, towards the hilus, a point will be found where the stimulus
causes a slight secretion ; as the electrodes are passed more peripherally,
the secretion increases, but it is rarely considerable, until the hilus of
the gland is reached. This means that a few of the nerve-cells,
outside the submaxillary gland, send their axis-cylinder processes to
the gland. It may be mentioned that the relative number of these
is greater in the rabbit than in the cat, and greater in the cat than
in the dog.

Similar conclusions as to the relation of the fibres of the chorda
tympani to the peripheral nerve-cells may be deduced from the experi-
ments in which the chorda tympani has been cut, and time allowed for
its fibres to degenerate. I shall deal later with these experiments
(p. 519); and it will be sufficient to give here the chief result which
bears on the question before us. When the chorda tympani, or the
chordo-lingual nerve, is cut in a dog or cat, and the peripheral cut end,
after about four days, is stimulated, no effect is produced ; but if a little
pilocarpine be injected, a fairly copious secretion is obtained, and the
blood fiow through the gland is increased. Although it is not agreed on
all sides that pilocarpine produces a secretion by stimulating the nerve-
endings in the glands, this is probably the case, and if it be so, the
experiment shows that the chorda tympani fibres have degenerated up
to the peripheral nerve-cells, whilst the fibres given off by the Uerve-
cells are still intact.

The position of the nerve-cells on the course of the chorda tympani
fibres to the sublingual gland can similarly be determined. If a
sufficient dose of nicotine be given to a dog, stimulation of the chordo-
lingual nerve has no effect ; stimulation of the ganglionic nerve-plexus,
lying in the angle between the chorda tympani and the lingual nerve,
causes constantly some secretion from the sublingual gland, but none, as
a rule, from the submaxillary gland. The ganglion, called by Bernard
the " submaxillary " ganglion, is the chief ganglion of this plexus ; it
follows, from what has just been said, that, at least in the dog, this
ganglion sends fibres to the sublingual gland, but commonly sends no
fibres to the submaxillary gland. It is, then, more accurate to speak of
it as the sublingual ganglion.

It is well known that there are snaall groups of nerve-cells in the tongue
itself; these, for the most part, are probably on the course of the chorda
tympani fibres to the glands, and to the small arteries of the tongue, but there
is no experimental evidence on the point.

The fibres of the chorda tympani pass through the geniculate
VOL. I. — ^i



482 THE SALIVAR Y GLANDS.

ganglion, but it is probable on general grounds that they are not con-
nected T\"ith the nerve-cells of this ganglion.

The nerve-strands which leave the chordo-lingual and the lingual
nerve to run to the sublingual and submaxillary plexuses consist in
very large part of small fibres, about 2 /a to 3-5 /a' in diameter,^ but a few
larger up to 8 or 10 ^ are also present. In the plexuses the number of
meduUated fibres decreases, and the number of non-medullated fibres
increases in passing towards the periphery. The axis-cylinder pro-
cesses, then, of most, if not of all, the peripheral nerve-cells are non-
medullated fibres.

The large nerve-fibres may occasionally be seen to divide. They are
probably sensory fibres for the gland arising from the fifth nerve. Some
of the small fibres may also be sensory.

Cranial nerve-fibres to the parotid and orbital glands. — The
course of the secretory and vaso-dilator fibres to the parotid gland varies
in different animals.

In the dog they arise from the ninth nerve ; they run — as Jacobson's
nerve — across the tympanic cavity over the promontorium forming part
of the tympanic plexus. From the tympanic cavity they proceed to the
small superficial petrosal and otic ganglion, and thence to the auriculo-
temporal branch of the fifth nerve, and so to the parotid gland.

In the sheep and ox the origin of the secretory fibres from the
medulla is not known. They run in the buccal branch of the fifth nerve,
instead of in the auriculo-temporal, leave this at the anterior end of the
masseter muscle, and run backwards to the parotid gland along the
duct.^

There are no experimental investigations on the place of connection
with nerve-cells of the cranial fibres to the parotid gland, but it has
been supposed that this connection occurs in the otic ganglion. No
ganghon cells have been described in the parotid gland itself.

The secretory fibres for the orbital gland of the dog run in the
buccinator branch ^ of the fifth nerve, and this is all that is known of
their course.

Historical. — The history of the discovery of the course taken by the
cranial secretory fibres * may be briefly summarised as follows : —

In 1851, LudAvig discovered in the dog secretory fibres for the sub-
maxillary gland in the lingual branch of the fifth nerve. Eahn (and Lndwig)
obtained in the rabbit secretion from the parotid, and sometimes from the sub-
maxillary gland, on stimulating certain cranial nerve roots, after removing the
brain. They found the effective nerve-roots to he those of the seventh and of
the fifth, but their experiments do not show satisfactorily that the secretory
fibres leave the medulla by way of these nerve roots.

Bernard showed that the secretory fibres of the submaxillary glands came
from the chorda tympani and so from the facial nerve. That the chorda
tympani had some connection with the flow of saliva from the submaxillary

1 Cf. Heideuhain, Arch. f. Anat. u. Physiol., Leipzig, 1883, Supp. Ed., S. 158 ;
Gaskell, Journ. Physiol., Cambridge and London, 1886, p. 29.

- Moussu, Arch. de2}hysiol. norm, etpath., Paris, 1880, p. 68. (Cf. this paper also for
secretory nerves of horse and pig.) Eckhard, CentralU. f. Physiol., Leipzig u. Wien,
1893.

* For the method of dissection for experimental purposes, see Heidenhain, Hermann's
"Handbuch der Physiol.," Bd. v. Th. 1, S. 38.

'' Ludwig, Ztschr. f. rat. Med., 1851, N. F., Bd. i. S. 255 ; Rahn, ibid., S. 285; Schiff,
Arch.f.physiol. IlciUc, Stuttgart, 1851, Bd. x. S. 581 ; Bernard, "Lefons sur la physioL et la



THE S YMF A THE TIC NER VE- FIB RES. 483

gland was suggested before Ludwig's discovery of secretory nerves, and was
definitely stated by Schiff in 1851.

The course of the nerve-fibres to the parotid gland was also investigated by
Bernard. He obtained secretion in the dog by stimulating the auriculo-
temporal branch of the fifth nerve, and a cessation of reflex secretion by ex-
tirpation of the otic ganglion. He considered that the secretory fibres came
from the small superficial petrosal nerve, and that the superficial petrosals
and the chorda tympani arose from the nervus intermedins of Wrisberg.
Abolition of the reflex secretion in the rabbit Avas observed by Schiff on simple
section of the small superficial petrosal. Loeb found that section of the
tympanic branch of the glosso-pharyngeal nerve {i.e. of Jacobson's nerve), or of
the roots of this nerve in the skull, also abolished the reflex secretion, so that
the secretory fibres of the small superficial petrosal come from the ninth and
not from the facial. And Heidenhain obtained copious secretion on stimulat-
ing Jacobson's nerve.

If the secretory fibres of the parotid really arise from the ninth- nerve, the
majority of the early observations form a singular record of inadequate experi-
ments and hasty deductions.

The sympathetic nerve-fibres and the nerve-cells with which
they are connected. — All the salivaiy glands receive nerve-fibres from
the cervical sympathetic. The fibres rim from the middle or from the
lower part of the superior cervical ganglion to the external carotid
artery, and accompany its branches. On the arteries they form a plexus
having two main longitudinal strands. The nerve-plexus, though chiefly
of non-meduUated fibres, contains some medullated fibres. In the artery
to the submaxillary gland of the dog, there are twenty to thirty
medullated fibres, a few of these being 5 /a, to 7 /^ in diameter, the rest
2 /A to 3-5 /i; the fibres run past the submaxillary ganglion in the hilus,
without being, so far as can be seen, connected with it.

The sympathetic fibres both secretory and vasomotor, for the sub-
maxillary gland of the dog and cat, arise chiefly from the second thoracic
nerve, to a less extent from the third, fourth, and to a slight and vary-
ing extent from the first and fifth thoracic nerves.^

Langendorff"^ found that four months after hemisection of the
spinal cord in the upper cervical region, the cervical sympathetic pre-
sented its normal appearance. We may conclude, then, that the
glandular nerve-fibres do not descend from a secretory centre in the
medulla, and simply make their exit by the upper thoracic nerve roots.

And there are several grounds for believing that the efferent sym-
pathetic nerve-fibres issuing from a particular nerve root are the axis-
cylinder processes of nerve-ceUs situated in the corresponding segment
of the spinal cord.

pathol. du systeme nerveux," 1858, tome ii, ; Schiff, "Lehrbuch. d. Muskel. u. Nerveu-
physiologie," 1858-1859, S. 393; Czermak, Sitzungsb. d. k. Akacl. d. Wissensch.,y^\.en,
1860, Bd. xxxix. S. 526 ; Beitr. z. Anat. u. Physiol. {Eckliard), Giessen, 1860, Bd. ii. S.
214 ; 1863, Bd. iii. S. 49 ; JSTavrocki, Stud. d. physiol. Inst, zu Breslau, Leipzig, 1865,
Heft 4, S. 123 ; Loeb, BeAtr. z. Anat. u. Physiol. {Eckhard), Giessen, 1869, Bd. v. S. 1 ;
Heidenhain, Arch. f. d. gee. Physiol., Bonn, 1878, Bd. xvii. S. 15 ; Bernard, " Lecons de
physiol. operatoire," 1879.

^ Langley, Phil. Trans., London, 1892, voh clxxxiii. p. 104.

-Arch. f. d. ges. Physiol., Bonn, 1894, Bd. Iviii. S. 165. Strictly speakmg, the
experiment only shows that the great majority of the nerve fibres of the cervical
sympathetic have their trophic centre in the spinal cord below the hemisection. If even
a considerable number of fibres had degenerated, they would have been absorbed in the
time allowed, and would have left no recognisable trace.



484 THE SALIVAR Y GLANDS.

The sympathetic nerve-fibres are connected witli nerve-cells in the
superior cervical ganglion. If the cervical sympathetic be cut, the end
towards the ganglion gives, in about four days, no effect on stimulation,
but stimulation of the ganglion itself or of the fibres beyond it causes
secretion and pallor of the gland (p. 522). On microscopical examination,
the nerve-fibres are found to be degenerated, as far as the ganglion
but not beyond it. Injection of nicotine causes for a time, varying with
the dose, effects like those caused by degeneration of the nerve.^ In
the cat even 5 mgrms. of nicotine may be sufficient to paralyse the cervical
sympathetic for a time, but very large amounts, e.g. 500 mgrms., do not
paralyse the nerves beyond the ganglion. From this and from other
facts we deduce that the sympathetic fibres are not connected with any
sympathetic nerve-cells peripherally of the superior cervical ganglion ;
and there are reasons for believing that they are not connected with
any nerve-cells between the ganglion and the spinal cord. In the dog
the cervical sympathetic is much less readily paralysed by nicotine.

Secretion of saliva produced by stirnLilation of the medulla
oblongata. — Bernard^ found that puncture of the fourth ventricle in
the dog causes secretion from all the salivary glands, and if the puncture
be a little above the spot, injury of which produces diabetes, the secre-
tion may be confined to the submaxillary gland, and from this gland may
be abundant. Loeb ^ showed that puncture of the medulla caused a greater
secretion from the submaxillary or the parotid gland, according as the
puncture was in the region of the nucleus of the ninth or of the seventh
nerve respectively. With puncture on one side, the effect on the sub-
maxillary gland of the opposite side was much greater than on the
parotid of the opposite side. Griitzner and Chtapowski ^ observed that
stimulation of the medulla oblongata caused abundant secretion if the
chorda tympani was intact, a slight secretion if it was cut, but none
after section of both the chorda and the sympathetic.

Secretion of saliva produced by stimulation of the cerebral cortex.
— It is not clear that the cortex of the cerebral hemispheres is connected
with secretion — or indeed with any visceral phenomenon — in the way
in which it is connected with the various body movements.

Stimulation of the motor area, taking the matter broadly, causes
secretion from the salivary glands, more readily than does stimulation of
any other part of the cortex. So far as the experiments go, the region
which causes maximum secretion from the submaxillary gland causes
also maximum secretion from the parotid. Apparently the secretion
ceases on cutting the cranial secretory nerve.

The experiments in which the portions of the cortex which cause
secretion have been mapped out were made on dogs under curari.
Those who have experimented on undrugged animals find that stimula-
tion of the facial area causes no secretion so long as the resulting move-
ment is confined to the facial muscles, and Eckhard^ states that the
secretion of saliva from the submaxillary glands only begins when the
stimulus is continued long enough, or is made strong enough, to induce

^ Lanji^ley and Dickinson, Froc. Roy. Soc. London, 1889, vol. xlvi. p. 425 ; Langley,
Journ. Physiol., Cambridge and London, 1890, vol. xi. p. 131.

^ " Le9ons de pliysiol. exp^'imentale," 1856, Bd. ii.

3 Op. cit., supra.

■* Arch. f. d. ges. Physiol, Bonn, 1873, Bd. vii. S. 522.

^Neurol. Centralhl., Leipzig, 1889, p. 65. Cf. also Bcitr. z. Anat. n. Physiol.
{Eckhard), Giessen, 1876, Bd. vii S. 199.



CHANGES D URING SE CRE TION. 485

general convulsions ; he considers that the saliva obtained in the
curarised animal is .due to an irradiation of nervous impulses, and not to
a localised cortical stimulation.

Ktilz 1 obtained no secretion from the submaxillary gland in unanfesthet-
ised dogs on stimulating the facial area, unless there was general tetanus, a
condition in which Braun ^ had already observed a flow of saliva from the
mouth. Lepine and Bochef ontaine ^ obtained secretion in curarised dogs by
stimulating the anterior portion of the cortex, including the facial area. The
secretion was more abundant on the side stimulated. Bochefontaine,'^ shortly
after, gave a more detailed account of the parts of the cortex from which
secretion could be induced ; secretion was obtained by stimulating spots on the
posterior part of the brain, and also by stimulating parts of the dura mater.
The experiments show little or nothing as regards the question whether there
are special areas in the cortex connected with the secretion.

Bechterew and Mislawsky ^ found, also on curarised dogs, that the region
which caused secretion when stimulated with weak currents was more limited
than that described by Bochefontaine. Stimulation of the anterior Sylvian and
anterior composite convolutions caused secretion from both the submaxillary
and parotid glands. Stimulation of the anterior limb of the sigmoid gyrus,
and of the anterior extremities of the coronal and anterior ecto-Sylvian con-
volutions, caused secretion from the submaxillary gland only. With stronger
currents, secretion was sometimes obtained from the more posterior portions of
the cortex. They found, unlike Lupine and Bochefontaine, no effect on
stimulating the orbital convolution.

Changes in Salivaey Glands during Seceetion.

The changes which occur in salivary glands during secretion are
progressive, and there is no sui3icient reason for believing that the
changes which occur in the cells at the end of a day's active secretion
differ in kind from those which occur in the first ten minutes.

The evidence is, it seems to me, decisively against the view that
during salivary secretion there is a breaking down of the mucous or of
other gland cells.*" If saliva at any stage of secretion is allowed to run
into alcohol, mercuric chloride, or other hardening reagent, disinte-
grating cells are not seen in the sediment as it forms, nor nuclei beyond
those which arise from the separated cells of Wharton's duct and from
leucocytes. And in the gland itself there is at no stage any sign of
active cell division ; the nuclei undergoing mitotic division are as rare
as they are in the resting gland.'^

Two fundamental changes undoubtedly take place in the gland cells
during secretion.

There is, first, an excretion of a greater or less amount of the sub-
stance which has been previously formed in the cells ; ^ this substance,

'^ CentralU. f. d. vied. Wissensch., Berlin, 1875, S. 419.

^ Beitr. z. Anat. u. Physiol. (EcJchard), Giessen, 1876, Bd. vii. S. 136.

2 Gaz. med. de Paris, 1875, p. 332.

* Arch, de pliysiol. norm. et2Mth., Paris, 1876, p. 161.

^ JVeiorol. Ccntralhl., Leipzig, 1888, p. 553.

'' It must be mentioned, liowever, that Heidenliain in his treatise (Hermann's
"Handbuch," 1890, Bd. v.) maintains the view originally advanced by him, that mucous
cells disintegrate to form part of the secretion.

■^ Langley, Proc. Roy. Soc. London, 1886, vol. xli. p. 362 ; Bizzozero, VlrcJioiv's Archiv,
1887, Bd. ex. S. 181.

^ Heidenhaih, Arch. f. d. ges. Physiol., Bonn, 1878, Bd. xvii. S. 43; Hermann's
"Handbuch," 1883 ; Lavdowsky, Arch. f. mikr. Anat., Bonn, 1877, Bd. xiii. S. 335.



486 THE SALIVARY GLANDS.

as it is formed, is for the most part, at any rate, stored up in the cells in
the form of granules.^

Secondly, there is a taking up of proteid material by the cells.^ This
occurs more or less exclusively in the outer part of the cells, and is the
chief cause of the formation of an outer non-granular zone.^ The taking
up of fresh proteid substance is usually spoken of as a growth of proto-
plasm ; we may use the expression as a matter of convenience, bearing
in mind that a large portion of the fresh proteid substance may be
simply deposited in interstices or larger spaces of the protoplasm.

It is probable also that, dming the whole period of secretion, there is
a conversion of the newly taken up proteid into the material for
secretion, or, in other words, the protoplasm is continuously disappearing
and giving rise to granules.

The loss of granules, together with the growth of ]3rotoplasm, causes
the gland to become less white and less opaque to the eye.

The nucleus, as was first shown by Heidenhain, is more obvious, and the
nucleolus more conspicuous, in sections of the active gland than in those of the
resting gland. The shrunken state of the nucleus in the resting gland appears
to he due to the action of the hardening agent, for in teased glands, when the
nucleus is visible, without serious alteration in the normal form of the cell, it
is seen to he spherical. Nevertheless it is probable that there is some increase
in the organic substance of the nucleus during prolonged secretion.

During rest ^ the protoplasm decreases and the granules increase, and
it would not be unnatural to suppose that no other changes take place in
the cells but those associated with the conversion of protoplasm into a
substance ripe for excretion. The point is one of great importance for
the proper understanding of the secretory processes. Is there or is
there not during rest any interchange between the cells and the lymph,



Online LibraryE. A. (Edward Albert) Sharpey-SchäferText-book of physiology; (Volume v.1) → online text (page 69 of 147)