Electrical Activity of the Heart Flashcards
why can the cardiac muscle be described as a functional syncytium?
the cells are connected by gap junctions that allow signals through and desmosomes that hold the cells together. these form intercalated discs that allow the cells to contract at the same time, as if they were one big cell
why does cardiac muscle need to relax after each contraction?
there is a long action potential which results in a long refractory period meaning it cannot exhibit tetanic contraction.
how long is the action potential in cardiac muscle compared to skeletal muscle?
cardiac it is 250msec but in skeletal it is 2msec
what is used to regulate the strength of contraction?
Ca2+ entry from outside the cell as it does not saturate the troponin.
what cell have unstable resting potentials?
pacemaker cells
what is responsible for the resting membrane potential on non-pacemaker cells?
> resting membrane potential: high permeability to potassium
what is responsible for the initial fast depolarisation in non-pacemaker cells?
> initial depolarisation: increase in permeability to sodium
what is responsible for the plateau in non-pacemaker cells?
> plateau: increase in calcium and decrease in potassium
what is responsible for the repolarisation in non-pacemaker cells?
the decrease in calcium and increase in potassium permeability
what is the resting potential of pacemaker cells due to?
> a gradual decrease in potassium permeability
an early increase in sodium permeability
a late increase in calcium permeability
what drugs will decrease the force of contraction?
calcium channel blockers
what drugs will increase the force of contraction?
cardiac glycosides
by how much will a temperature increase affect the heart rate?
10 beats/min/degree centigrade
what is the effect of hyperkalaemia?
high plasma potassium will cause fibrillation and heart block
what is the effect of hypokalaemia?
low plasma potassium will cause fibrillation and heart block
