Pacemaker Physiology
REVIEW SESSION
What do you know about electrical
activity in the heart?
 What are common terms used when talking about electrical
activity/impulses in the body?
Key Terms:
Autorhythmic
Repolarization
Action potential
Ions/ion channels
Permeability
Threshold
Membrane potential
Depolarization
Cardiac Conduction
System
Autorhythmic cells
 Modified cardiac muscle cells (Nodal cells)
 1% of cardiomyocytes
 Function independently (influenced by ANS/hormones)
 “Pacemakers”
Conduction pathway:
 SA node fires
 Electrical impulse spreads through myocardium of BOTH
atria
 AV node fires
 Impulse spreads down AV bundle & bundle branches
 Purkinje fibers distribute impulse through myocardium in
both ventricles
Nodal Cell
Action Potentials
Unstable resting
membrane potential
 Called “pacemaker
potentials”
 Starts at about -60mV
and drifts upward
 Action potential is
triggered when
threshold voltage is
reached
Phases:
Phase 4: Spontaneous
depolarization
 K+ channels closed
 Slow inflow of Na+
 Causes membrane potential to rise
0
3
0
Phase 0: Depolarization
 Threshold reached (-40mV)
 Fast Ca++ inflow
 Peaks around 0 mV
Phase 3: Repolarization
 K+ channels open  Fast K+ outflow
 Ca++ channels closed
 Membrane potential back to
-60 mV
4
4
3
Activity!!
Get in groups
Act out nodal action potential
◦ 2 people CA++
◦ 2 people K+
◦ 1 person Na+
Worksheet
Other resources:
http://www.cvphysiology.com/Arrhythmias/A004
http://www.pathophys.org/physiology-of-cardiac-conduction-and-contractility/
Khan Academy (www.khanacademy.org)
◦ Search “action potential in pacemaker cells”