Conducting System, nerve supply and Arch of Aorta.pptx

Heart

1. Conduction, Nerve Supply of Heart and Arch of Aorta

2. Sinuatrial node (SA node) : It is known as the ‘pace maker’ of the heart. It is situated in the upper part of the crista terminalis. The impulses from the SA node reach atrio-ventricular node.

3. Atrio-ventricular node (AV node) : It is located in the triangle of Koch, which is placed in the lower part of the inter atrial septum.

4. Atrio-ventricular bundle (AV bundle/bundle of His) It begins from the AV node traverses the membranous part of the interventricular septum and then divides into right and left branches. The right branch passes to the right side of the interventricular septum. Majority of the fibres enters septo-marginal trabecula (moderator band) to reach the base of the anterior papillary muscle. The left branch is distributed in the wall of the left ventricle. Purkinje fibres form a subendocardial plexus.They are larger and somewhat paler then ordinary myocytes

5. The AV node is damaged by various forms of heart disease. The only route for impulse transmission from the atria to the ventricles is through the AV node. Therefore, damage to this node is called ‘heart block’ , interferes with the ability of the ventricles to receive the impulses. Without these signals, the ventricles beat at an intrinsic rate that is slower than that of the atria and too slow to maintain adequate circulation. In such cases an artificial pacemaker set to discharge at the appropriate rate is usually implanted.

6. Nerve supply to the heart Though the cardiac muscle contracts rhythmically and automatically, the nerves supplying the heart alter the cardiac rate. Parasympathetic stimulation has negligible effect on coronary blood flow, but sympathetic stimulation constrict the epicardial arteries and dilates intra- muscular arteries. Atria and conducting system of the heart are innervated by both sympathetic and parasympathetic nerves, however ventricular muscle is supplied only by parasympathetic nerves

7. Cardiac plexus Superficial cardiac plexus - below the arch of aorta and in front of the right pulmonary artery. Deep cardiac plexus - in front of the bifurcation of the trachea.

8. Formation of superficial cardiac plexus A branch from the left superior cervical sympathetic ganglion. Lower cervical cardiac branch of the left vagus nerve. Formation of deep cardiac plexus Cardiac branches of the both (right and left) cervical sympathetic ganglia (except from left superior) Cardiac branches form the upper four or five thoracic sympathetic ganglia Cardiac branches of the both vagus (except lower cervical cardiac branch of left vagus) Sympathetic fibres increase the heart rate and cardiac output and parasympathetic fibres diminish it. Sympathetic fibres produce vaso-dilatation in intramuscular branches and vaso-constriction of epicardial arteries. Sympathetic fibres also carry pain sensation from the heart

9. Superior cervical sympathetic ganglion Upper thoracic sympathetic ganglia Vagus nerve Superficial C. Plexus Deep C. Plexus Lower cervical cardiac

10. Arch of Aorta Continuation of ascending aorta. Situated in superior mediastinum behind manubrium sterni Begins behind rt. 2 nd chondrosternal joint At commencement – bulb of aorta Termination- left 2 nd chondrosternal joint Presents 2 curvatures- one convex above, other convex in front and to left.

11. Infront and to left: 4 nerves & 1 vein- left phrenic, inferior cervical cardiac branch of Lt.vagus , sup cer cardiac branch of Lt.symp trunk, Lt vagus Left superior intercostal vein Relations

12. Behind & right: Deep cardiac plexus Trachea Left rec laryn nerve Esophagus Thoracic duct 4 th thoracic vertebra Relations

13. Relations Above: Brachiocephalic trunk Lt. common carotid a. Lt. subclavian a. Brachiocephalic vein Lt phrenic n. Lt vagus

14. Relations Below : Lt principal bronchus Pulmonary trunk Ligamentum arteriosum Superficial cardiac plexus Left recurrent laryngeal nerve

15. Branches Brachiocephalic trunk Left common carotid Left subclavian Occassional Arteria thyroidea ima

16. Anomalies Right sided aortic arch Double aortic arch Abnormal origin of right subclavian artery Coarctation of aorta Applied Aortic knuckle