The action potential starts at the ... node and is ... at the ... node before entering the ... ... ...
SA Delayed AV Bundle of His
conduction through the Bundle of His and the Purkinje fibres is extremely ...
The ventricles depolarise from ...cardium to ...cardium
True or false, the heart depolarises from base to apex?
False - it depolarises from apex to base
Which heart cells show intrinsic audtorhythmicity?
SAN AVN Purkinje fibres
Describe 2 features of auto-rhythmic cells in the heart
They pass their excitation and hence their contraction to each other
Intercalated discs connect adjacent cardiac muscle cells
What is the natural pacemaker of the heart? What rate does it beat at?
A beat generated outside the normal pacemaker is an ... beat
The ... pacemaker of the heart normally drives the heart and ... other pacemakers
The AVN pacemaker beats at ...-... bpm, and the Bundle of His "safety net" beats at ...-...
Depolarisations of auto-rhythmic cells rapidly spread to adjacent cells through ... ...
Why do myocardial contractile cells have a different looking action potential to myocardial auto-rhythmic cells?
Due to the presence of calcium channels
Intercalated discs in the amongst the heart cells allow.....
branching of the myocardium
4 structural features of cardiac cells
Intercalated discs Gap junctions Many mitochondria Large T tubules
Describe the process of cardiac contractile cell muscle excitation, contraction and relaxation (10)
1. AP enters from adjacent cell 2. VGCCs open, Ca2+ enters cell 3. Ca2+ induces Ca2+ release from ryanodine receptor channels 4. Local release causes Ca2+ spike 5. Summed Ca2+ sparks create a Ca2+ signal 6. Ca2+ binds to troponin to initiate contraction 7. Relaxation occurs when Ca2+ unbinds troponin 8. Ca2+ is pumped back into SR for storage 9. Ca2+ is exchanged with Na+ 10. Na+ gradient is maintained by Na+/K+ ATPase
ECGs ... each individual membrane potential from contractile cells
Atria contract just ... p-wave is formed on the ECG recorder
PR segment represents...
conduction through AVN
T wave represents...
If wave of contraction moves toward positive electrode what deflection do you see on ECG? And what do you see if wave is moving away?
Towards - upward Away - downward
Waveform on ECG gives indication of where cardiac axis vector is moving relative to ...
Mean axis of polarity of heart exists as a ...
3-lead ECG leads and colour: Red - Yellow - green - Black -
Red - right arm Yellow - left arm Green - left leg Black - right leg (earth lead)
Name the 3 unipolar leads
aVR, aVL, aVF
aVR normally has a ... deflection
Name locations of chest leads
V1 - 4th ICS, right sternum V2 - 4th ICS, left sternum V3 - between V2 and V4 V4 - 5th ICS MCL V5 - 5th ICS anterior axillary line V6 - 5th ICS mid axillary line
V1 and V2 represent ... aspect of heart
V3 and V4 represent ... aspect of heart
V5 and V6 represent ... aspect of heart
Inferior aspect of heart is represented by leads...
II, III, aVF