Electrical Activity of the Heart Flashcards
Control of cardiac myocyte contraction
Action potentials initiated, regulated and conducted by pacemaker cells
Primary pacemaker of the heart
Sino-atrial node
Sino-atrial node function and conduction speed
Pacemaker
0.5m/sec
Annulus fibrosus function
Non-conducting cells that separate the atrium and ventricles.
Only cells not connected by gap junctions
Atrioventricular node function and conduction speed
Delay box
0.05m/sec
Bundle of His function
Travels inferiorly between ventricles and transmits AV node impulses to the ventricles.
Located at the inferior end of the interatrial septum
Purkinje fibre function and conduction speed
Rapid conduction system: 5m/sec.
Most release GABA neurotransmitter which exerts inhibitory actions on certain neurons and thereby reduces transmission of nerve impulses
Excitation-contraction coupling
AP triggers myocyte contraction
Functional syncytium
Single cells act as one cell as they are connected:
- physically by desmosomes
- electrically by gap junctions
Resting membrane potential of myocyte
Negative (inside)
- Potassium predominant inside
- Sodium and calcium predominant outside
Ion gradients maintained by ion pumps
Pacemaker cells resting membrane potential
Unstable: around -60 mV
Pacemaker cells - reach pacemaker potential
- Spontaneously -60 mV -> -40mV
2. Sodium ions enter cell
Pacemaker cells - depolarisation
-40 mV -> +10 mV
Calcium ions into cell
Pacemaker cells - repolarisation
+10 mV -> -60 mV
Potassium out of cell
Contractile cells resting membrane potential
Stable: around -90 mV
High resting intracellular potassium
