electrical activity of the heart Flashcards
why is cardiac action potential long?
due to L-type Ca2+ depolarisation
state what P wave, QRS complex and T wave correspond to:
P wave - atrial depolarisation
QRS complex - ventricular depolarisation
T wave - ventricular repolarisation
what is the atrioventricular node?
delay box
the only pathway through which action potentials can reach the contractile fibres of the ventricles.
describe the special conducting system:
SA NODE → AV NODE → BUNDLE OF HIS → PURKINJE FIBRES → APEX
what is the function of the bundle of his and Purkinje’s fibres? state the conduction rate:
they are both specialized conducting cells of the ventricles, a rapid conduction system.
conduction rate ~ 5 m/sec
define the AV node and state the conduction rate:
they are myocardial cells involved in the conduction of action potential, connecting the atria and ventricles.
conduction rate ~ 0.05 m/sec (delay box - gives time for atria to contract)
what is the only non conducting part of the heart that separates the atrium from the ventricles?
annulus fibrosus
where does depolarisation begin? state the condution rate:
SA node, which is the main pacemaker of the heart
depolarisation speed determines heart rate
conduction rate ~ 0.5 m/sec
why does the depolarisation phase occur in a pacemaker cell?
due to an increase in PCa2+ (L-type)
describe the pacemaker potential:
- unstable membrane potential
- starts at -60mV
[0] hyperpolarisation
[1] slow depolarisation - PNa+ influx
[2] rapid depolarisation - PCa2+ (Pf) influx
[3] repolarisation - PK+ efflux
describe the non pacemaker action potential
[0] rapid depolarisation - increase in PNa+, opening of sodium channels
[1] initial depolarisation - closing of sodium channels
[2] plateau - increase in PCa2+ (L-type) and a decrease in PK+
[3] repolarisation - decrease in PCa2+ and an increase in PK+
[4] Na/K pump, sodium out and potassium in.
state the reason why the resting membrane potential is -90mV in a non-pacemaker cell:
due to high resting Pk+
what is the main difference between the action potential of the myocardial contractile cell and those of skeletal muscle fibres and neurons?
The myocardial cell has a longer action potential due to Ca2+ entry
what does summation in skeletal muscle lead to?
tetanus
fatal if it happened in the heart.
state the significance of cardiac muscle having a long action potential:
longer than the skeletal action potential
~2 msec (skeletal) compared to ~250 msec
[1] long refractory period (the time during which the muscle cannot contract again after an action potential)
- prevents tetanic contraction
[2] Ca2+ entry from outside the cell can regulate contraction
why do the actin-myosin binding sites not become fully saturated in cardiac muscle, compared to skeletal muscle?
Allows regulation by controlling Ca2+ levels.
state the functions of desmosomes and gap junctions in the heart:
desmosomes (physical connection) and gap junctions (electrical connection) cause the heart cells to contract as one big muscle
-> forms intercalated discs.
Together these form a functional syncytium
