Electrical Activity of the Heart Flashcards
Cardiac muscle cannot demonstrate tetanic contraction; what is tetanic contraction?
Sustained contraction due to high frequency of action potential firing
What two features comprise the gap junctions of cardiac muscle?
Electrical connection and physical connection vis desmosomes
Describe the length of cardiac muscle contraction?
~250msec - longer than skeletal (approx. 2msec)
Why can cardiac muscle not exhibit tetanic contraction?
Long refractory period
What can be said about the effect of calcium on cardiac muscle troponin?
It does not saturate the troponin - therefore it can regulate the strength of its contraction
Some cells have unstable resting membrane potentials - what are theses cells called?
Pacemaker cells
Name common modulators for pacemaker cells?
- Neural control
- Temperature
- Drugs
- Ion concentrations
What effect does temperature have on heart rate?
10 beat increase/min/degree celsius
What effects does potassium concentration have on heart rate?
Hyperkalaemia - atrial fibrillation and heart block (bradycardia)
Same with hypokalaemia
What effect does calcium concentration have on heart activity?
Hypercalaemia - increased HR and force of contraction
Hypocalaemia - decreased HR and force of contraction
The action potential of cardiac muscle is propagated from what voltage to what voltage?
-80mV to +20mV
What is tetanic contraction?
Sustained contract due to high frequency of action potentials firing
Outline the process of excitation-contraction coupling in cardiac muscle?
- Influx of calcium ions to sarcoplasmic reticulum
- Calcium ions bind to calmodulin
- Calcium-calmodulin complex binds to myosin light chain kinase
- Kinase phosphorylates myosin X-bridge with ATP
- Tension gained and contraction occurs
How are cardiac myocytes physically associated?
Desmosomes
