Topic 11 Flashcards
2 major parts of the cardiac physiology
- heart
- conduction system
Heart
dual pump with valves
Muscle cells of the heart connected by..
gap junctions
Conduction system produces
aps spontaneously (no stimulus) but at different rates
Conductions system is composed of…
non contractile cardiac muscle cells
Non contractile cardiac muscle cells are ..
modified to initiate and distribute impulses throughout the heart
4 parts of the conduction system
- sinoatrial (SA) node
- atrioventricular (AV) node
- bundle of His (AV bundle) and bundle branches
- purkinje fibres
Sinoatrial (SA) node
in right atrium. produces APs faster than other areas (pacemaker)
Sinoatrial node rate =
100 APs/min (modified by PSNS to be 75 aps/min at rest)
Atrioventricular (AV) node location and rate =
in right atrium . 50 aps/min
Bundle of His (AV bundle)
originates AV node. only route for electrical activity to go from atria to ventricles
Bundle branches
right and left. 30 APs/min
Purkinje fibres
terminal fibres stimulate contract of the ventricular myocardium
Purkinje rate
30 APs/min
Artificial pacemakers
stimulate if SA or AV node damaged
If conduction system damaged ..
next faster part becomes pacemaker (if SA damaged then AV node takes over)
Cells of the APs of SA and AV nodes
non contractile autorhythmic cardiac muscle cells (self excitable) and -40mV is threshold
Pacemaker potenital
- low K permeability (K voltage gates closed).
- slow inward leak of Na (Na voltage gates open)
- causes slow depolarization toward threshold (-40mV)
AP depolarization for pacemaker potential
- at threshold –> AP
- Ca voltage gates open so Ca moves in and depol. (Na voltage gates close at threshold so not involved in AP)
- Ca voltage gates close at peak
AP repolarization for pacemaker potential
- K voltage gates open at peak so K out leads to repol.
- K gates close below thereshold
Na channels open at -50 mV for pacemaker potential then it..
starts pacemaker potential again. once K gates close so a continuous cycle.
Note for pacemaker activity
NO RMP!!
APs in ventricule myocardium
- cells = contractile.
- purkinje fibre AP –> ventricular (contractile) myocardial AP (spread cell to cell by gap junctions)
- Resting MP= -90 mV
Depolarization of ventricular myocardial APs
- Na voltage gates open fast = same gates as neuron, skel. muscle.
- MP to +30 mV