Electrical and mechanical activity of the heart Departemen Fisiologi Fakultas Kedokteran Universitas Sumatera Utara
Oct 24, 2014
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