Physiology Flashcards
Where is the SA node located?
The upper right atrium
Near where the SVC enters the right atrium
Do the cells in the SA node have a stable resting membrane potential?
No
What is spontaneous pacemaker potential?
Where membrane potential is taken to a threshold to generate an action potential in the SA nodal cells
What causes the pacemaker potential?
Decrease in K+ efflux
Slow Na+ influx (the funny current)
What causes the rising phase of the action potential?
Depolarisation caused by activation of voltage gater Ca2+ channels
(CALCIUM INFLUX)
What causes the falling phase of the action potential?
Depolarisation caused by activation of K+ channels
K+ EFFLUX
How does excitation spread through the heart
SA node Cell-to-cell conduction AV node Bundle of His Left & right branches Purkinje fibres
How does excitation spread from SA node to AV node?
Via gap junctions
Why is conduction delayed in the AV node?
Allows atrial systole (contraction) to precede ventricular systole
What causes phase 0 of the ventricular muscle action potential?
Fast Na+ influx
What causes phase 1 of the ventricular muscle action potential?
Closure of Na+ channels and transient K+ efflux
What causes phase 2 (plateau phase) of the ventricular muscle action potential?
Mainly Ca2+ influx
What causes phase 3 of the ventricular muscle action potential?
Closure of Ca2+ channels and K+ efflux
What is phase 4 of the ventricular muscle action potential?
Resting membrane potential
Which nervous system mainly influences heart rate?
Autonomic Nervous System