Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol 1: A-Dea
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit25759/730/
718 
CONTRACTILITY. 
on the surface, closing the eyelids when the 
eyes are offended by bright light, swallowing, 
breathing, coughing, sneezing, vomiting, ex¬ 
pulsion of fæces and urine, &c. consequent 
on certain sensations of the fauces, lungs, air- 
passages, nostrils, stomach, rectum, or blad¬ 
der. Such muscular actions, excited by irri¬ 
tation of distant parts, have been generally but 
vaguely described as the effects of Sympathies 
of one part of the living body with another. 
It is well ascertained that they are effected 
through the motor nerves (or certain of the 
motor nerves) of the muscles concerned in 
them ; and their dependence on the Sensations, 
and therefore on the sensitive nerves, of the 
parts from the irritation of which they originate, 
has been sufficiently illustrated by Haller, 
Whytt, Monro, and others.* 
It has also been observed, by Haller and 
Whytt, but more frequently and carefully by 
Legallois,f Flourens, and Mayo,* that in 
many animals, (most remarkably in cold¬ 
blooded, or young warm-blooded animals,) 
even after the removal of the brain, as long 
as the circulation can be maintained, move¬ 
ments of the kind now in question go on, 
or may be excited by irritation of the sur¬ 
faces; and that if the spinal cord be divided 
into several parts by transverse sections, such 
movements may still be excited in the muscles 
supplied from each part, by irritation of the 
portion of the skin which has its nerves from 
that part of the cord. These facts have (as is 
believed) usually been thought to denote, that a 
certain degree of Sensation remains under these 
circumstances, in connection with the living 
state of the spinal cord, or of portions of the 
spinal cord, and medulla oblongata, indepen¬ 
dent of the brain ; and that it is still through 
the intervention of sensation, that irritation 
of the surface of the body excites any con¬ 
traction of muscles. Dr. Marshall Hall has 
lately described phenomena precisely of this 
description, under the title of Excito-motory 
phenomena, and as proofs of what he terms 
the Reflex Function of the Spinal Chord § 
—a power of exciting contraction in mus¬ 
cular fibres connected with it, which he 
supposes that organ to possess, equally inde¬ 
pendently of sensation as of volition ;|| and as 
it seems hardly possible to be quite certain of 
the existence of Sensation in the case of the 
mutilated animal, this language is perhaps 
philosophically correct ; but the probability of 
the existence of Sensation in such circum¬ 
stances must be allowed to be very great ; and 
at all events, that sensation is an essential part of 
* It is obvious that such motions, excited di¬ 
rectly by sensations, cannot be accurately distin¬ 
guished from those voluntary actions which are 
called Instinctive, as being prompted by the in¬ 
stincts, distinct from strictly intellectual acts, 
which are linked by nature with the sensations of 
certain parts of the body. 
t Expériences sur le Principe de la Vie. 
% Outlines of Physiology, second edit. p. 282, 
and Anat. and Physiol. Comms. 
§ Phil. Trans. 1833, p. 635. 
)| See particularly p. o40. 
the connection between the irritation of distant 
parts, and the excitement of involuntary mus¬ 
cular contractions of voluntary muscles, for 
useful purposes, in the entire and healthy 
body,—may be held to be a point well esta¬ 
blished by the observations of Haller, Whytt, 
Monro, and others, on such sympathetic actions. 
Accordingly, those actions, in the entire body, 
which Dr. M. Hall ascribes to the reflex func¬ 
tion,* are the same, or similar to those, which 
have been fully treated by Dr.Whytt and others 
as sympathetic actions, or actions of voluntary 
muscles excited by sensations. 
But Dr. Hall has fixed the attention of phy¬ 
siologists on this class of facts, and has illus¬ 
trated by experiments their independence of 
the Brain, and dependence on the Spinal Cord 
exclusively, and in this conclusion he is sup¬ 
ported by many facts previously recorded by 
Le Gallois, Magendie, Flourens, and others. 
It is further to be observed, that the contrac¬ 
tions of voluntary muscles, which are supplied 
by the nerves of the Symmetrical class of Sir 
C. Bell, while they are excited through the one 
set of filaments comprising those nerves, are 
made known to our consciousness by the others 
or sensitive filaments, and constitute the im¬ 
portant class of Muscular Sensations. Of the 
movements of the strictly involuntary muscles, 
the heart, stomach, and bowels, and even the 
bladder, (supplied by irregular nerves,) we 
have, in the perfectly healthy state, no intima¬ 
tion, although they frequently become percepti¬ 
ble to us in disease, or when over-excited. But 
contractions of some of these involuntary mus¬ 
cles also are pretty certainly excited by certain 
-Sensations, as, e.g. a certain degree of antipe- 
ristaltic movement in the stomach by the feel¬ 
ing of nausea, and a certain movement of the 
pharynx and oesophagus by the sensations in 
the fauces, which prompt the act of deglutition ; 
and in such cases, although not attended with 
consciousness, they are in all probability excited 
through the nerves of these muscular parts. 
Accordingly, the pharynx and oesophagus have 
been observed by Mr. Mayo, and the stomach 
by Breschet, Milne Edwards, and others, to 
be exceptions to the general rule of involuntary 
muscles being inexcitable by irritation of their 
nerves. 
The old distinction of muscles into Volun¬ 
tary, Involuntary, and Mixed, is very deficient 
in precision, so far as the last class is concerned. 
The true distinction is, of muscular contrac¬ 
tions, into those excited in the natural state by 
Mental Stimuli, and through the intervention 
of Nerves (qui soli in corpore mentis sunt mi- 
nistri)—and those excited by Physical Stimuli, 
acting on the muscles themselves, whereas the 
intervention of nerves is a theory, not an esta¬ 
blished fact. The first class admits obviously, 
from what has been stated, of a division into 
movements excited by the Will, which depend 
on the Brain, and movements excited by invo¬ 
luntary mental acts, especially by Sensations, 
which depend only on the Spinal Cord and 
medulla oblongata. The Will acts only on 
* P. 653 et seq.
        

Nutzerhinweis

Sehr geehrte Benutzer,

aufgrund der aktuellen Entwicklungen in der Webtechnologie, die im Goobi viewer verwendet wird, unterstützt die Software den von Ihnen verwendeten Browser nicht mehr.

Bitte benutzen Sie einen der folgenden Browser, um diese Seite korrekt darstellen zu können.

Vielen Dank für Ihr Verständnis.