Cardiac Pacemaker Potential and Cardiac Conduction Flashcards
What percentage cells make up autorhythmic cells?
1%
Define automaticity.
Spontaneous rhythmic action potential generation
What is the dominant cardiac pacemaker?
SA node
What is the SA node regulated by?
Autonomic nervous system and circulating hormones
What does the rate of decay of Vm determine?
Heart rate
What are the differences between SA action potential and ventricular action potential?
SA has a lack of a stable membrane potential
SA has a less negative Vm due to few Kir channels present
SA action potential between -40mV and -55mV
Phase 1 does not exist in SA
Describe phase 4 of the SA node AP.
Na+ influx through F-type channels
At -ve Vm Na+ entry is favoured over K+
Inward depolarising Na+ current, if
Kv inactivate - reduced outflow of K+ ions (ikv)
What happens in Phase 0 of SA node AP
T-type Ca2+ channels activated
Membrane depolarizes
L-type Ca2+ channels activated
Full depolarization
What happens in Phase 2 of SA node AP
Closure of T-type channels
Membrane begins to repolarize
Describe what happens in Phase 3 of SA node AP
2 Kv channels opened
Ikr - rapidly activating delayed outward rectifying current
IKs - slowly activating delayed outward rectifying current
Contribute to next pacemaker potential
What is the role of the conduction fibres?
Rapidly conduct AP initiated by pacemaker cells to myocardium
What are the conduction fibres?
Bundle of His and Purkinje fibres
Where is the SA node located?
Right atrial wall close to superior vena cava
What are the features of pacemaker cells?
Small, fewer myofibrils and fewer intercalated discs
What is the role of fascia adherens?
Anchor actin filaments of terminal sarcomeres
