Electrical activity of the heart Flashcards
What forms a functional syncytium?
Cardiac muscle
How is the cardiac muscle form a functional syncytium?
electrically connected via gap junctions
physically connected by desmosomes
these form the intercalated discs
Does cardiac muscle have long or short AP?
Long
What is the effect of having a long AP on refractory peroid and tetanic contraction?
long refractory period, so cannot exhibit tetanic contraction
What can Ca entry regulate?
Ca2+ entry from outside cell can regulate contraction
Ca2+ release does not saturate the troponin, so regulation of Ca2+ release can be used to vary the strength of contraction.
Why do some cells act as pacemakers?
Some cells have unstable resting membrane potential
they act as pacemakers
Describe the non-pacemaker action potential
Resting membrane potential
high resting PK+
Initial depolarisation
increase in PNa+
Plateau
increase in PCa2+(L-type), and decrease in PK+
Repolarisation
decrease in PCa2+, and increase in PK+
Describe the pacemaker potential
Pacemaker potential (= pre-potential) not a simple story! Due to a ... gradual decrease in PK+ early increase in PNa+ (= PF) late increase in PCa2+ (T-type)
Action potential
increase in PCa2+ (L-type)
What does pacemaker explain?
Autorhythmicity
What is the effect of temperature on heart rate?
Increase in T,
increases ~10 beats/min/ºC
Describe the effect of hyperkalemia
fibrillation & heart block
Describe effect of Hypokaelemia
fibrillation & heart block (anomalous)
Describe effect of Hypercalcemia
increased HR & force of contraction
Describe effect of hypocalcemia
decreased HR & force of contraction
What is the sinoatrial node and where is it?
Right atrium pacemaker
~ 0.5 m/sec
and triggeres first depolarization
