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Conduction in the heart. 5. 6. 1. 7. 2. 3. 4. 8. Specialised cardiac muscle cells. Contractile cells Mechanical work of pumping Autorhythmic cells Initiating and conducting action potentials. Autorhythmic cells. Cardiac contractile muscle cells. Spread of excitation.
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Specialised cardiac muscle cells • Contractile cells • Mechanical work of pumping • Autorhythmic cells • Initiating and conducting action potentials
Autorhythmic cells Cardiac contractile muscle cells
Spread of excitation • Atrial excitation • Interatrial pathway • Internodal pathway (~30ms to reach AV node) • Conduction between the atria and the ventricles • AV nodal delay (~100ms) • Ventricular excitation • Bundle of His • Purkinje fibres (~30ms delay)
Action potential of contractile cells • Rising phase • Activation of VG-Na+channels • Na+ rapidly enters the cell • Plateau phase • Maintained by 2 voltage-dependent permeability channels • Activation of ‘slow’ L-type Ca2+ channels • Marked decrease in K+ permeability • Occur due to the sudden change in voltage during the rising phase of the action potential
Action potential cont’d • Falling phase • Inactivation of Ca2+ channels • Delayed activation of VG-K+ channels • Returns resting potential to polarisation
