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Related article: responds to nicotin in the usual manner. The effects on the Auerbach
ganglia can also be located; these are stimulated by atropin and nicotin;
these and the other autonomic poisons Motrin 600 also act more peripherally.
Peripheral Reflexes in Other Organs. The intestines are the most prominent,
but by no means the only, example of reflex response in the absence of central innervation.
In fishes and amphibians, for instance, the iris of the excised eye responds to light, even
after removal of the retina (Steinach, 1892); blood vessels regain their tone when their
nervous connections degenerate, etc. These reflexes do not even Motrin 600 involve the presence
of peripheral nerve cells. They may be considered as survivals of the reflex mechanism
of the lower invertebrates (Parker, 1909). This conception may help to elucidate some
obscure pharmacologic phenomena.
Extrinsic Innervation of the Intestine. Sympathetic nerves, running through the
superior and inferior splanchnic and mesenteric ganglia, supply the whole tract, from
the cardia to the anus, mainly with inhibitory fibers.
The parasympathetic supply consists of the augmentory erigens and pelvic nerves to
the anus, rectum and colon; and the vagus fibers, distributed from the esophagus to
the end Motrin 600 of the ileum. The vagus innervation causes a short primary inhibition, followed
by marked stimulation. It is not known whether the extrinsic nerves connect with the
local nerve cells; or whether they act independently on the muscle; or both. The bulbo-
sacral innervation seems useful mainly for initiating tone, which is then maintained by
the local mechanism. The initial inhibition fayors the ingress of the chyme (Cannon,
1911). The "roll movements" which propel the contents for long distances, are of
extrinsic origin, due to vagus stimulation with simultaneous depression of sympathetic
inhibition (Meltzer and Auer, 1907).
Differences of Rhythm at Various Levels. In intact animals, the rhythm is faster
toward the two ends of the intestine than toward the middle. In excised intestine, the
rate decreases with the distance from the pylorus, the rate of the duodenum in rabbits
being about 50 per cent, faster than in the lower ileum. The oral end is more irritable
and therefore acts as pacemaker. It is also less Motrin 600 subject to epinephrin relaxation. Its
tone is also higher. On the Motrin 600 other hand, the slower rate of the aboral end is accompanied
by greater excursions (Alvarez, 1914, 1915).
The Intrinsic Neuro-muscular Mechanism. The segmentation (pendulum) move-
ments and the ordinary peristaltic movements are entirely of peripheral origin, since
they are observed also in the excised intestine even when the mucosa and submucosa are
removed. They are Motrin 600 originated Motrin 600 peripheral to the ganglia; for they persist, under suitable
conditions, for five days after death, when the ganglia must be dead; and they can also
be evoked in preparations from which the ganglia have been removed anatomically
(Gunn and Underbill, 1914). The rhythmic segmentation movements are automatic,
the peristaltic movements are evoked reflexly (as in the Bayliss-Starling reflex; a pinch
causes the intestine to constrict for i or 2 cm. above, and to relax for some 30 cm. below
the stimulus). The local nerve-muscle mechanism for these reflexes consists of the
longitudinal and circular muscular coats, innervated by Auerbach's plexus of nerve
cells and fibers, which lies between Motrin 600 them. This communicates also with Meissner's
plexus in the submucosa, which innervates the glands, muscularis mucosae, etc., but
which is not concerned in the intestinal movements.
Isolation of Intestinal Coats. Magnus, 1904, found that the muscular coats of the
cat's intestine could be separated into layers, so as either to retain or eliminate Auer-
bach's plexus. Motrin 600
PERIPHERAL AUTONOMIC SYSTEM 275
The "plexus preparations" contain the peripheral nerve cells, and respond to con-
tinued stimulation by rhythmic contractions.
The plexus-free preparations (which contain only the nerve-endings and muscle)
ordinarily respond to continued stimulation by a single tetanic contraction, like ordi-
nary smooth muscle; but if the preparations are carefully protected against injury, they
also resume spontaneous rhythmic movements after a time (Gunn and Underbill, 1914).
With the disappearance of spontaneous movements by exposure, the reaction to all
drugs, even barium, is abolished. The response to pilocarpin and 'atropin disappears
before that for epinephrin or barium, indicating that the parasympathetic innervation
dies before the sympathetic (Gunn and Underbill).
The muscularis mucosee also contracts, especially in the diagonal direction. Its
rhythm is slow, rather similar Motrin 600 to that of the spleen. Its tone and rhythm are increased
by epinephrin. Barium causes marked tonic contraction, abolishing the rhythm (Gunn
Localization of the Action of Poisons on the Intestine. The use of
excised intestine, and of plexus and plexus-free preparations, aids in the
localization of the action of poisons.
If a given action occurs in the excised intestine, the point of attack
must be local. If the action occurs in plexus preparations, and not in
plexus-free strips, it must be on the ganglion cells. If it occurs in the
plexus-free preparations, it must be on the endings or muscle. No reli-
able method has been found to distinguish between the nerve-endings and
muscle; or between the endings of the extrinsic and intrinsic system, if the
two be distinct. All conclusions as to these are based on the insecure
ground of analogy.
This general method as outlined only discovers the most peripheral point of attack,
which is practically the most important; but it does not exclude that the poison may also
affect more central structures at the same time. This possibility is not merely theoreti-
cal; for even this method shows that the same drug may attack different structures,
according to the dose and other conditions. The conditions have not been fully ana-
lyzed, and until this has been done, the localization of the intestinal phenomena must
be rather unsatisfactory. The following exposition is mainly along the lines laid down
by Magnus (the Ergebnisse der Physiologic, vol. 7, 1908, and vol. 2, 1903), and by Hans
Meyer (Meyer and Gottlieb's Lehrbuch).
Action of Drugs on the Intestinal Movements. Barium salts provoke very violent
contraction; the effect occurs in plexus-free preparations and is presumably (from anal-
ogy) exerted directly on the contractile substance. It is abolished only by the very
large doses of atropin which paralyze the muscle substance.
Strophanthin (and presumably the other Digitaloid drugs) stimulate in small doses
and inhibit in large doses. The effects occur in plexus-free preparations, and hence
involve the endings or muscle, presumably the latter. The stimulation is abolished
only by the extreme doses of atropin.
Physostigmin, Pilocarpin, Muscarin, Cholin and Colchicin produce
violent irregular contractions, and also tetanic contraction of plexus-fret-
preparations. Their action must be postganglionic; Motrin 600 presumably stimula-
tion of the vagus endings.
The stimulation of these drugs is abolished by small doses of atropin;
pilocarpin is antagonized by extremely minute doses; physostigmin requires
relatively the largest amount.
Atropin. The effects and their localization differ Motrin 600 according to con-
ditions: Very small doses have no effect on the normal intestine, but remove '
intestinal spasm, due to peripheral vagus stimulation (physostigmin,
pilocarpin, etc.; lead colic, anemia of intestine, etc.). The motor response
to stimulation of the vagus trunk is lessened, but not abolished. This
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