Cardiac skeleton

ANATOMY

1. FIBROUS SKELETON OF THE HEART

2. FIBROUS SKELETON OF THE HEART A] composed of dense connective tissue. B] lies in the plane between the atria and the ventricles. C] This plane corresponds to atrioventricular groove/ orifices of heart. RV RV LV LV

3. D] is Present in the form of circular fibrous ring,, interconnected by intervening fibrous tissue. E] surrounds the four valves

4. F] There are four such rings-- ,, for four orifice of heart i & ii- - Atrioventricular rings – for tricuspid opening & for bicuspid opening. It is 8-shaped iii- aortic ring - --------- at root of aorta iv- pulmonary ring------ at root of pulmonary trunk superior view of AV-plane (Front) posterior

5. G] Rings are interconnected 1] AV-ring is connected to AORTIC ring by a large mass of fibrous tissue called trigonum fibrosum dextrum . 2] Mitral ring is connected to aortic ring by small mass of fibrous tissue called trigonum fibrosum sinistrum 3] Pulmonary ring & aortic ring are connected by tendon of infundibulum . m m

6. trigonum fibrosum dextrum . trigonum fibrosum sinistrum Aortic valves pulmonary valves

7. 1 . It forms the central support of the heart 2 .Provides attachment to i - bicuspid & tricuspid valves directly ii -cardiac muscle fibres of atria & ventricles iii- membranous part of interventricular septum 3. Keeps the cardiac valves competent 4. Acts as an electrical insulator It blocks the direct spread of electrical impulses from the atria to the ventricles. Impulses go only through bundle of His. 5. prevents overdilation of the valve openings H] FUNCTION OF FIBROUS SKELETON Applied – weakening of it may lead to cardiac valves incompetence--- means incomplete closure leading to mitral regurgitation, aortic regurgitation, tricuspid regurgitation, ..

8. NOTE tricuspid valves & mitral valves are directly attached to ring semilunar valves are directly attached to wall of vessel ,, not to ring

9. Conductive system of the heart Conductive system of the heart is ---- --made up of specialised cardiac muscle fibres,, -- responsible for initiation and conduction of cardiac impulse/A.P ,, by its own. ---- these impulses cause cardiac muscle contraction

10. Components of Conducting System are: 1] Sinoatrial node/ SA node 2] Atrioventricular node/ AV node 3] Atrioventricular bundle [ bundle of His ] 4] Right and left branches of AV bundle (of His) 5] Purkinje fibers

11. SA node Also k/a node of Keith & Flack Situated in the wall of Rt. Atrium ,in the upper part of sulcus terminalis just below the opening of SVC. It is called PACEMAKER of the heart bcz it generates impusle &initiates the contraction of cardiac muscle producing heart beat. Impulse travels through atrial wall to reach the AV node impulse or heart beat or heart rate=70-100 beat/min. [average approx.70/min.]

12. Atrioventricular node/ AV node Also k/a node of Tawara Smaller than SA node Located in the traingle of Koch /or / in the lower & dorsal part of the atrial septum just above the opening of coronary sinus It generates impulse at the rate of 40-60 beat /min.

13. Atrioventricular bundle [bundle of His] It begins from AV node &crosses the AV ring & travel along the interventricular septum.[membranous part]. Divides at the upper part of muscular part of IV-septum. Divides into two branches– Rt. & Lt. Bundle branch

14. Bundle branch Right branch of AV bundle— Passes down on right side of interventricular septum. Large part of it enters the moderator band to reach anterior wall of Rt. Ventricle , where it divides into purkinje fibres. Likewise,, Left branch of AV bundle— goes on left side in left ventricle.

15. Purkinje fibres These are terminal branches of Rt. & Lt. Branches of Bundle of His. Form sub- endocardial plexus. They generates impulse at the rate of 20-35 beat /min. applied- -- arrhythmia – it is loss of normal rhythm of contraction/ heart beat. -- due to damage of conductive system. blood supply – nearly whole conductive system except left branch AV bundle –is supplied by RCA. Left br. Of AV bundle by LCA.

16. Heart is myogenic 1] Means A.P. is generated by muscle itself,, not by nerve. 2] Conductive system of heart is made up of cardiac muscles. 3] Nerves supplying the heart, can only influence / modify the rate of impulse production or A.P. 4] If all nerves are cut even then heart will continue to beat.[d/t impulse from SA node] 5] Sympathetic nerve stimulation increase the rate of impulse generation. 6] Para-Sympathetic [ vagus ] nerve stimulation decrease the rate of impulse generation.

17. Conductive system of the heart is made up of specialised cardiac muscle fibres,, which is responsible for initiation and conduction of cardiac impulse/A.P ,, by its own. [ process of impulse generation /A.P. independent of nerve supply.]MEANS---- if all nerve connections to the heart are cut , even then the heart continues to produce A.P. & beat/CONTRACT rhythmically. Hence our heart is myogenic .

18. BUT sympathetic & parasympathetic nerves can modify the heart rate & force of contraction. Sympathetic stimulation increase heart rates & force of contraction Para-Sympathetic stimulation decrease heart rates & force of contraction

19. Innervation Although the heart’s inherent rate of contraction is set by the SA node, this rate can be altered by extrinsic neural controls

20. Innervation The nerves to the heart consist of visceral sensory fibers Parasympathetic fibers that slow heart rate Sympathetic fibers that increase the rate and force of heart contractions

21. 19- 24 Cardiac Conduction System 1 2 3 4 5

22. 1. Sinoatrial (SA) node Right atrium 2. Internodal pathway 5a. Right branch of bundle of His Right ventricle 6. Purkinje fibers Left ventricle 5b. Left branch of bundle of His 4. Bundle of His or AV bundle 3. Atrioventricular (AV) node Interatrial pathway 19- 25

23. Interatrial pathway Right atrium Left atrium SA node Internodal pathway AV node Purkinje fibers Right ventricle Left ventricle Bundle of His 1 st beat 2nd beat 19- 26

24. 19- 27 Our focus

25. The fibrous skeleton of the heart lies in the plane between the atria and the ventricles Muscles of atria is not in continuity with muscles of ventricle [d/t fibrous skeleton] This fibrous skeleton is bad conductor of electrical impulse. So it prevents direct entry of electrical impulse from atria to ventricle. 4. ACTS AS AN ELECTRICAL INSULATOR :

26. Electrical impulse from atria to ventricle goes through bundle of Hiss only. Although each cardiac muscle has capacity to generate & conduct (carry) electrical impulse. Thus fibrous skeleton helps in coordinated conduction of A.P. or electrical impulse to ventricle.-------- coordinated ventricular contraction.