Читать книгу Manual of Equine Anesthesia and Analgesia - Группа авторов - Страница 75

 Unlike most physiologic systems, neither the autonomic nor motor neurons are necessary for initiating cardiac contractions.

 The heart can continue beating in the absence of outside neural control because the cells of the specialized electrical conducting system of the heart are capable of automatic rhythmical depolarization or “self‐excitation.” This is due to:Cell membranes that are “leaky” or permeable to sodium ions.Increased permeability to potassium and calcium ions also plays a role in the spontaneous depolarization of the pacemaker cells.A resting cell membrane potential that is not adequately negative to keep sodium channels closed.The resting membrane potential of cardiac conducting cells is −60 to −70 millivolts (mV) and that of the SA node is −55 to −60 mV (compared to −90 mV for other cell membranes).