1. Heart –Electrical Properties
Prof. K. Sivapalan

2. Electrical Properties
Introduction.
Function of the blood is transport of substances.
Function of the heart and vessels are:
Keeping blood flowing.
Delivering more blood to needy tissue.
2013
Electrical Properties

3. Design of the circulatory system.
All blood goes to lungs in pulmonary circulation
The blood flows to all other organs [including heart] in systemic circulation.
2013
Electrical Properties

4. Electrical Properties
Structure of the heart.
2013
Electrical Properties

5. Components of the pumping system.
Collectors- atria.
Pumps- intermittent pump – ventricles.
Regulators of flow - valves.
Rhythm control – conducting system.
Adjustments – by autonomic nerves and hormones.
2013
Electrical Properties

6. Electrical Properties
Location of the heart.
In the mediastinum.
Hanging on the large vessels.
Lying on the diaphragm.
Supported by fibrous pericardium.
2013
Electrical Properties

7. Properties of cardiac muscle.
Branching cells.
Separated by intercalated discs – tight junctions with pores permeable to ions. [electrical continuity]
Functional syncytium.
Striations – similar to skeletal muscles.
2013
Electrical Properties

8. Sarcomere, filaments and fibrils.
Z lines – centre of actin filaments.
M line – centre of myosin filaments.
A band – length of myosin filaments.
Sarcomere is a unit of myofibrils between two Z lines.
2013
Electrical Properties

9. Myofibrils and T tubular system.
Myofibrils - bundle of actin + myosin [Yellow]
Mitochondria [blue].
Sarcoplasmic reticulum + T tubules [pink] at Z line.
Intercalated discs at Z line [light blue].
Central nucleus [purple].
2013
Electrical Properties

10. Excitation contraction coupling.
Action potential spreads across intercalated discs.
Spreads along T tubules [Z line] to Terminal cistern.
Calcium released from cistern and influx from ECF.
Actin myosin binding and sliding.
Removal of Calcium results in relaxation.
2013
Electrical Properties

11. Electrical Properties
Contraction.
Actin and myosin do not overlap in a relaxed muscle.
Calcium binding to Troponin C initiates sliding.
Contraction can not reduce length to zero.
In heart, there will be residual blood after maximal contraction.
2013
Electrical Properties

12. Electrical properties of cardiac muscle.
Resting membrane potential – 85 – 95 mV.
Depolarized to +20 mV.
Rising phase – 2 m sec.
Plateau – sec in atrium and 0.3 in ventricles.
Refractory period – 0.3 sec.
2013
Electrical Properties

13. Ionic basis of action potential.
Depolarization – sodium influx.
Plateau – calcium influx and potassium efflux.
Repolarization – potassium efflux.
Na+.
Ca++
K+.
2013
Electrical Properties

14. Origin of Cardiac Impulse.
Pacemaker – junctional tissue.
Pacemaker potential – after each impulse declines to firing level.
Rate of action potential depends on the slope of the prepotential.
It is due to reduction of K+ efflux (↑ by Ach) and then increase in Ca++ influx (↑ by NA).
Ca++ T (transient) channels complete prepotential and L (long lasting) action potentials [no sodium] in nodal tissues.
SA node – 120/min, AV node – 45/min, Purkinje system – 35/min.
First area to reach threshold will be the pace maker.
Origin of Cardiac Impulse.
2013
Electrical Properties

15. Electrical Properties
Spread of impulse.
SA node.
Inter nodal pathways & atrial musculature.
AV node.
Bundle of His.
Bundle branches – Purkinje fibers.
Cardiac muscles through intercalated discs.
2013
Electrical Properties

16. Spread of impulse in the heart.
SA node to AV node.
Nodal delay.
Septum – left to right.
Apex and wall – from inside outwards.
Towards base.
Examination – ECG.
2013
Electrical Properties