1. CARDIAC MUSCLE Dr. Abdelrahman Mustafa Department of Basic Medical Sciences Division of Physiology Faculty of Medicine Almaarefa Colleges

2. Learning Objectives By the end of this lecture you should be able to Identify the types of cardiac muscle cells Define the cardiac muscle Autorhythmicity Describe the pace maker potential Define the cardiac muscle excitability Describe the Ventricular potential Define the cardiac muscle contractility Describe the mechanism of cardiac muscle contraction Define cardiac muscle conductivity Identify the conductive system of the heart Describe the starling law of the heart

3. CARDIAC MUSCLE 3Layers: Epicardium, Endocardium Myocardium, 4 Chambers Rt atrium Rt Ventricle Lt atrium Lt ventricle 4 large vessels Aorta Pulmonary artery Vena Cava Pulmonary veins 4 Valves Tricuspid Mitral Aortic Pulmonary

4. Types of Cardiac Muscle Cells Contractile CellsContractile Cells –99% of Cardiac Muscle –Do mechanical work of contraction –Do not generate action Potential in normal conditions (Can generate Action Potential in abnormal conditions) Autorhythmic cells:Autorhythmic cells: –Initiate Action Potential –Conduct Action Potential Do not contractDo not contract Interconnected by intercalated discs and form functional syncytia Within intercalated discs – two kinds of membrane junctions –Desmosomes –Gap junctions

5. Cardiac Muscles Action=Action of Pump 5

6. 6 What are the Properties that allowed the Cardiac Muscles to Act as PUMP?

7. AUTORHYTHMICITY Definition Is the ability of cardiac muscle to contract in self regular constant manner IS IT MYOGENIC OR NEUROGENIC IN ORIGIN ? MYOGENIC This is evident by :- 1)The frogs apex beating After deinnrevetion in Ringr Lactate soulation 2)The embryo heart started to beat BEFORE CNS DEVELOPMENT

8. AUTORHYTHMICITY Cardiac autorhythmic structure that initiate AutoRhythmicity Called PACE MAKER spontaneous depolarization to threshold is known as PACE MAKER POTENTIAL 8

9. AUTORHYTHMICITY( PACE MAKER POTENTIAL ) PHASES OF PACEMAKER POTENTIAL Prepotential Causes : Na + going inside(Infflux ) Ca ++ going inside(Infflux ) ↓ K + going outside(Efflux) After Prepotential we get Depolarization and Repolarization Depolarization Cause: Ca ++ going inside(Infflux ) Repolarization Cause : K + going outside(Efflux)

10. EXCITABILITY Definition is the ability to respond to stimuli by generation action potential. The resting membrane potential of the contractile fibers is stable at about– 90 mV. Once myocardial cells are stimulated by action potential originating in PACEMAKER, it produces its own action potential Action Potential of ventricular muscle fiber has four phases 0, 1, 2, 3,4.

11. MEMBRANE POTENTIAL (mV) -90 0 0 1 2 3 4 TIME 0 = Rapid Depolarization (inward Na + current) (inward Na + current) 1= Early partial repolarization 2 = Plateau (inward Ca ++ current) 3 = Repolarization (outward K + current) 4 = Resting Potential Excitability (Myocardial Action Potential ) PHASE

13. EXCITABILITY

14. CONTRACTILITY Definition The ability of cardiac muscle to convert chemical energy to mechanical work Ca 2+ entry through L-type channels in T tubules triggers larger release of Ca 2+ from sarcoplasmic reticulum – Ca 2+ induced Ca 2+ release leads to cross-bridge cycling and contraction – 90% of Ca 2+ needed for contraction comes from sarcoplasmic reticulum Excitation-Contraction Coupling in Cardiac Contractile Cells

15. CONDUCTIVITY Defienion Is the ability of cardiac muscle fiber to conduct cardiac impulses that are initiated in SA node, which is the pacemaker of the heart 1. Sinoatrial (SA) node 2. Atrioventricular (AV) node 3. Atrioventricular bundle (bundle of His) 4. Bundle branches 5. Purkinje fibers The conductive system

16. Cardiac Muscle Mechanics Starling ’ s law of the heart :- Law states that : with in physiological limit, the force of myocardial contraction is directly proportional to the initial length of the cardiac muscle fibers

17. 10 MINs for study

18. Q1 The cells that responsible to convert the chemical energy to mechanical work called A)Contractile Cells B)Autorhythmic cells: C)Conductive cells D)Desmosomes

19. Q2 Pacemaker depolarization caused by : A)Na+ Infflux B)Ca++ Infflux C)K+ Efflux D)Ca++ Efflux

20. Q3 the ability to respond to stimuli by generation action potential known as : A)cardiac muscle Auto rhythmicity B)cardiac muscle excitability C)cardiac muscle contractility D)cardiac muscle conductivity

21. Q4 Starling’s law of the heart Describe the relationship between : A) Contraction and cardiac muscle Length B) Contraction and cardiac muscle conductivity C) Contraction and cardiac muscle excitability D) Contraction and cardiac muscle Auto rhythmicity

22. References Human physiology by Lauralee Sherwood, 7 th edition Text book physiology by Guyton &Hall,12 th edition Text book of physiology by Linda.s contanzo,third edition 22