Electrical Activity of the Heart Flashcards
Why does cardiac muscle have a longer depolarisation time than skeletal muscle?
To allow for regulation of the amount of calcium getting into the cell, the calcium released inside the cell and so the strength of contraction
In cardiac muscle what effect does a long refractory period have?
Stops the cardiac muscle from exhibiting tetanus
What does cardiac muscle form to allow it to function as a unit?
A functional syncytium
What allows the functional syncytium to work?
Gap junctions - electrical connections
Desmosomes - physical connections
What is a functional syncytium?
A group of cells that are synchronised electrically in an action potential
Why does cardiac muscle have a long refractory period?
Because it has a long action potential
What do cardiac muscle cells with unstable resting membrane potentials act as?
Pacemakers
In non-pacemaker cells what causes the plateau?
Increase in calcium ions inside the cell because of L-type calcium channels
Decrease in potassium ions inside the cell
In non-pacemaker cells what is the initial depolarisation caused by?
Increase in sodium ions inside the cell
How is the pacemaker potential generated?
Gradual decrease in potassium ions
Early increase in sodium ions
Late increase in calcium ions by t-type channels
What drugs modulate the electrical activity of the heart?
Calcium ion channel blockers
Cardiac glycosides
What do calcium ion channel blockers do?
Decrease force of contraction
What do cardiac glycosides do?
Increase force of contraction
How does temperature effect electrical activity of the heart?
Increases it by 10 beats per minute for each degrees increase
What does hyperkalemia do to the heart?
Fibrillation and heart block