Nerve Fibrils in the Sino-Auricular Node

Abstract

PLATES 65-67.The purpose of the following paper is to describe nervous structures found within the sino-auricular node by the use of a vital stain of methylene-blue. Since the original description by Keith and Flack ( I ) in 19o7, considerable interest has attached to the sinoauricular node; and its normal histology, its function, and' its condition in pathological hearts have been actively investigated. As regards its function, the experimental evidence points strongly to it as the primum movens of the heart (2, 3, 4), although a very few observers apparently are not inclined to accept this view as yet (5, 6, 7). Its relation to certain clinical conditions, more especially to auricular fibrillation (pulsus irregularis perpetuus), is being studied, but so far the reports on the hearts examined consist in the main of descriptions of the findings in and around the node without any assertion that the changes in the node account for the clinical condition.Pathological changes of the intranodal nervous structures have not received much attention; indeed thus far no one has described the finer nervo~s elements occurring normally within the node. In addition to the numerous studies of the general cardiac nervous system, both intra-and extracardiac, which have extended over many years, three recent important contributions to the nervous structures of the auriculo-ventricular system have been made; namely, those of Wilson (8), De Witt (9), and Engel (IO). Wilson was the first to demonstrate by means ,of a vital stain not only

Slowing down as we age: aging of the cardiac pacemaker’s neural control

“…By analyzing hearts from eels, salmon, frogs, lizards, turtles, moles, mice, cats, a kangaroo, a dolphin, humans, and even a whale, Keith and Flack identified inside the sino-auricular junction a conserved region of characteristic primitive wavy fibers which exhibited a close connection with the terminals innervating the heart. This led them to hypothesize that this region was the origin of the heart's rhythm and the main target for the heart's neural control; further studies would prove them right [15][16][17]. The pacemaker is located next to the right atrium and delimited to the left by the crista terminalis, to the bottom by the inferior vena cava, and to the top by the superior vena cava (Fig.…”

The Origin and Conduction of the Heart Beat

“…The sarcoplasm is relatively large in amount and the fibrillae much less numerous than in the usual cardiac muscle fiber. Nuclei are present in large numbers and nerve fibers and ganglia are abundant within and near the node (9), (10). Both nodes also receive a special and profuse blood supply.…”