Section 48.3.3 (Exam 4) Pacemakers Flashcards
Heart Function Depends on Properties of Cardiac Muscle
What is the function of pacemaker cells?
Pacemaker cells generate rhythmic sequences of action potentials without input from the nervous system
Do pacemaker cells contract?
Pacemaker cells don’t contract
How do action potentials spread through cardiac cells?
Cardiac cells are in electrical contact with each other through gap junctions that ion current can flow through
What is essential for pumping blood efficiently?
Large groups of cardiac muscle contracting in unison
What is the sinoatrial node and where is it located?
It is the primary pacemaker located at the junction of the superior vena cava and the right atrium
Describe the resting membrane potential of primary pacemaker cells in the sinoatrial node.
It gradually increases until it reaches the threshold to trigger an action potential
This ensures a constant pumping of the heart
Describe the action potentials triggered by the sinoatrial node.
The action potentials are slower to rise, broader, and slower to return to resting potential than those of neurons and other muscle cells
Describe ion channels in pacemaker cells.
They are different than in other cardiac cells
There are Na+, Ca2+, and K+ channels
What makes the resting potential in pacemaker cells less negative than other cardiac cells?
Na+ leak channels are open contributing to constant depolarization until threshold
The rounder shape of an AP graph shows how it is slower to rise and fall. Why does the AP of pacemaker cells have a rounder shape on its graph?
Action potential is due to voltage-gated Ca2+ channels, which open and close more slowly than Na+ channels
What happens as the MP becomes less negative in pacemakers?
Some Ca2+ channels open causing the MP to rise further
These are called T-type Ca2+ channels because they open transiently (temporarily)
Which ion channels open in pacemaker when the threshold is reached?
L-type (long-lasting) Ca2+ channels, which generate the action potential
In pacemakers, the MP slowly moves upward in between APs. What causes this slow rise?
Influx of Na+ followed by Ca2+ (T-type) creating a more positive internal environment
K+ channels are closing, stopping positive charge from leaving the cell
Describe what happens in the AP of a pacemaker.
L-type Ca2+ channels open causing an influx of Ca2+
Resting potential returns to normal by opening of K+ channels
