A textbook of human physiology / translated from [the] 6th German edition by W. Stirling.

  • Landois, Leonard
Date:
1888
Catalogue details

Licence: Public Domain Mark

Credit: A textbook of human physiology / translated from [the] 6th German edition by W. Stirling. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

    130/980 page 78
    single, at others double, and it can be seen as a white crescent when the heart is lifted up and looked at from behind (lig. 54). The cardiac nerves proceed downwards on the auricular septum, exchanging fibres in their course to join two ganglia at the auriculo-ventricular groove, and known as Bidder's ganglia (fig. 57). It has been stated by one observer that the bulbus arteriosus contains ganglionic cells, but this is denied by others.] According to Openchowsky, every part of the heart (frog, triton, tortoise) contains nerve- fibres which are connected with every muscular fibre. In the auricles, at the end of the non- mcdullated fibre, a tri-radiate nucleus exists which gives off fibrils to the muscular bundles. There is a network of fine nerve-fibres distributed immediately under the endocardium—these fibres act partly in a centripetal direction on the cardiac ganglia, and are partly motor for the endocardial muscles. The parietal layer of the pericardium contains (sensory) nerve-fibres. The following kinds of nerve-cells are ioxmii.—unipolar cells, the single processes of which after- wards divide ; bipolar pyriform cells (fig. 56), which in the frog possess a straight (?i) and usually also a spiral process (o). 58- THE AUTOMATIC MOTOR CENTRES OF THE HEART.—(1) It is generally assumed that the nervous centres which excite the cardiac movements, and maintain the rhythm of these movements, lie within the heart, and that they are probably represented by the ganglia. (2) There are—not one, but several of these centres in the heart, which are connected with each other by conducting paths. As long as the heart is intact, all its parts move in rhythmical sequence from a principal central point, an impulse being conducted from this centre through the conducting paths. What the discharging forces of these regular progressive movements are, is unknown. If, however, the heart be subjected to the action of diffuse stimuli {e.g., strong electrical currents), all the centres are thrown into action, and a spasm-like action of the heart occurs. The dominating centre lies in the atirides, hence the regular progressive movement usually starts from them. If the excitability is diminished, as by touching the septum with opium, other centres seem to undertake this function, in which case the movement may extend from the ventricles to the auricles. According to Kronecker and Schmey, in the dog^s heart there is a spot above the lower limit of the upper third of the ventricular septum, which, when it is injured, e.g., by destroying it with a stout needle, brings the heart to a stand- still ; this has been called a co-ordinating centre. (3) All stimuli of moderate strength applied directly to the heart cause at first an increase of the rhythmical heart-beats ; stronger stimuli cause a diminution, and it may be paralysis, which is often preceded by a convulsive movement. Increased activity exhausts the energy of the heart sooner. (4) Single very weak stimuli, which have no effect on the heart when applied singly, if repeated sufficiently often, may become active owing to summation of the stimuli {v. Basch). (5) Even the weakest stimulus which can excite a contraction always causes an energetic contraction, i.e., the minimal stimulus causes a maximal effect {Boivditch, Kronecker and Stirling). Fig. 57. Fig. 58. Scheme of nerves of frog's heart. R. Remak's, and B, Bidder's gan- glia ; S.V., sinus venosus ; A, auricles; V, ventricle; B.A., bulbus arteriosus ; vag, vagi. Staunius's experiment. A, auricle ; V, ventricle ; S. V., sinus venosus. The zig-zag lines indicate which parts continue to beat; in 2 the ventricle beats at a different rate.
    digitised image 1
    digitised image 2
    digitised image 3