Sinoatrial node
The sinus node ( Node sinuatrialis ), also Sinuatrial node ( SA node ) or Keith - Flack node, the primary electric clock of the heart action. It is located in the right atrium ( right atrium ) of the heart in the mouth of the superior vena cava, the so-called sine venarum cavarum. " Sine " or " Sinuatrial " are thus derived from the location of this clock. It is part of the excitation education system of the heart. Due to the sinus node sinus rhythm arises.
Anatomy
The term node is actually somewhat misleading because it is not really palpable or visible nodes (in the sense lymph nodes or tumor). It is the sinus node only electrically locations as the area of the heart where the electrical excitation is first detectable.
In the human heart of the sinus node is spindle-shaped (2-3 cm long) close to the epicardium at the junction between the superior vena cava and rechtsatrial. You may, however a significant deviation in position of the sinus node. The blood supply is done by a single strong atrial Koronararterienast proximally arises from the right coronary artery in the majority of normal heart. Moreover, there exists a Kollateralenversorgung with other vascular branches of atrial vasculature. The transatriale anastomotic circulation may act as a bridge between the two main coronary trunks ( right coronary artery, left Zirkumflexzweig ). The venous drainage is done directly into the right atrium through thebesische channels.
Histology
Histologically, the sinus node from a group of specialized cardiac muscle cells that have the ability to spontaneous depolarization, making Himself can electrically excite. This is done in the idle state in adult humans at a frequency of 60-80/min. In extremely physically well-trained endurance athletes but occurs due to the enlargement of the heart 40/min also rest pulse rates below. Compared with cells of the Arbeitsmyokards they have fewer myofibrils and mitochondria, so they are less hypoxieanfällig.
Function
Created in the sinus node excitation passes through the working muscles of the atria - according to some authors of so-called Internodalbündel - to the following components of the conduction system of the heart ( AV node, His bundle, bundle branch, Purkinje fibers). These other parts of the conduction system are capable of spontaneous depolarization, but is not due to a lower and lower frequency in the normal state is applied to ensure that the sinus node is the only clock.
Striking the action potential of the sinus node depolarization is immediate after the repolarization. This is due to HCN channels ( hyperpolarization activated cyclic nucleotide gates ) which can be opened by hyperpolarization. The resulting sodium inward current is also called I- funny.
The sinus node is affected by nerves and hormones. He is under the influence of the sympathetic and parasympathetic nervous system. The parasympathetic nervous system exerts with its transmitter acetylcholine at rest constantly a rate reducing (negative chronotropic ) effect on the sinus node. By one separates the branches of the vagus nerve of the parasympathetic nervous system, the heart beats faster permanently. Under stress, the sympathetic nervous system increases with its transmitter norepinephrine, the discharge frequency of the sinus node (positive chronotropy ). The same effect of adrenaline and noradrenaline, the hormones reach than the sinus node via the bloodstream.
Dysfunction
Various dysfunction of the sinus node manifest as bradycardia and tachycardia complicated cardiac arrhythmias in the group of diseases of the sick sinus syndrome.
A complete failure of the sinus node is called sinus arrest. Skips a not a child of impulse formation area, there is an acute cardiac arrest. This is rare, because subordinate centers ensure a while to slow but sufficient in resting heart rate in healthy hearts. If the sinus arrest does not lead to sudden death, it is now relatively simple and permanently fix with a pacemaker.
Nomenclature
The studies by Arthur Keith and Martin Flack followed a short time later on the detailed publication Sunao Tawaras through the AV node ( 1906). Tawara had branching cords of muscle described, the starting running from the atria both sides of the interventricular septum, and suspected that it had to be on an impulse line and distributive system. Tawara described a node structure that originally wanted to investigate Keith and Flack also. However, they found a similar nodal structure at a different anatomical site and suspected in the parent pacemaker center of the cardiac motion. Keith himself called the structure found by him according to morphological aspects of Sino - auricular node (1907). The synonym sinus node coined W. Koch (1907, 1909). The experimental- physiological confirmation of sinus node function provided Thomas Lewis and Wybau 1910 with the ECG technology independently.
Quote
" I. ( a) The muscular connection in the heart of lower order between the sinus and auricular canal, and in the heart of higher order between those performing parts of the heart is narrow. In the latter fibers lead directly from this link to the vicinity of the AV bundle. ( b ) The Aurikularkanal connection is highlighted at this point by a thickening of the heart wall. ( ... ) II ( a) shows a remarkable relic of persistent primitive fibers to the sino- auricular junction in all studied mammalian heart. These fibers are in close contact with the vagus and sympathetic nerves, they have a special arterial supply; It is assumed here that the movement of the heart rhythm is normally determined is formed. " ( Arthur Keith, Martin Flack 1907)