Electrical and mechanical activity

of the heartDepartemen Fisiologi

Fakultas Kedokteran

Universitas Sumatera Utara

• The heart contracts, or beats, rhythmically as a result of action potential that it generate by itself autorhythmicity.

Conducting System of the Heart

AV Node

Posterior Inferior Fascicle

Anterior Superior Fascicle

Septal Depolarization Fibers

Purkinjie Fibers

Inter- nodal Tracts

Bundle of HIS

Left Bundle Branch

Right Bundle Branch

SA Node

Cardiac muscle cells

• Two classes of cardiac muscle cells

1) Auto rhythmic cells : Specialized muscle cells of conducting system

2) Contractile cells

Pacemaker potentialPacemaker potential

If channels; Ca2+influx through T (transient), then L (long

lasting) channel

ELECTRICAL PROPERTIES

The resting membrane potential -90 mV

• Action potential in cardiac contractile cell Travels down T tubules Entry of small amount of Ca2+ from ECF Release of large amount of Ca2+ from sarcoplasmic reticulum Troponin - tropomyosin complex in thin filaments pulled aside Cross-bridge cycling between thick and thin filaments Thin filaments slide inward between thick filaments Contraction

“Excitation (Depolarization of plasma membrane)”

Opening of voltage-sensitive plasma membrane Ca2+ channels in T tubules

Flow of Ca2+ into cytosol

Ca2+ binds to Ca2+ receptor on the external surface of the sarcoplasmic

reticulum

Opening Ca2+ channels intrinsic to these receptors

Flow of Ca2+into cytosol

↑ Cytosol Ca2+ concentration

Contraction

Spread of cardiac excitation

Spread of cardiac excitation

• Depolarization in SA node spreads radially through the atria, then converges on the AV node.

• Atrial depolarization is complete in about 0.1 s

• Conduction in AV node is slow, about 0.1 s (AV nodal delay) before excitation spreads to ventricles.

• From top of septum, depolarization spreads conducting Purkinje

fibers to all parts of ventricles in the 0.08-0.1 s.

• Activation anteroseptal region ventricular myocardium

• Activation major portion ventricular myocardium from endocardial surfaces

• Late activation posterobasal left ventricle and pulmonary conus

Physiological regulation of contractile force

(1) length – tension relation (2) chemically induced rises in the

calcium store leading to higher sarcoplasmic Ca2+ concentration in systole; (sympathetic neurotransmitter and cathecholamine.)

Relation of Tension to Length in Cardiac Muscle

• Starling's law of the heart or Frank-Starling law = "energy of contraction is proportional to the initial length of cardiac muscle fiber."

= relation between ventricular stroke volume and end-diastolic volume

Relation of Tension to Length in Cardiac Muscle

• The length-tension relationship in cardiac muscle is similar to that in skeletal muscle as the muscle is stretched, the developed tension increases to a maximum and then declines as stretch becomes more extreme.

Factors that normally increase or decrease the length of ventricular

= Length of muscle fiber = preload

Myocardial Contractility

Kurva Frank StarlingS

trok

e vo

lum

e

End Diastolic Volume

Normal

Stimulasi Adrenergik

Fungsi jantung

Syok Kardiogenik