Cardiac Electrophysiology. Flashcards
The AV Valve:
Regulates the movement of blood between the two chambers.
The atrium wall contains less ______ than the ventricular wall:
Cardiac muscle.
More cardiac tissue in the left ventricle than the :
Why?
Right ventricle.
This is because the left ventricle needs more pressure to drive blood from through the systemic circuits.
Cardiac muscle tissues are linked by:
Electrical synapses.
Cardiac electrical synapses are located:
Located in specialized structures called intercalated disks.
They allow for fast synchronized responses to stimuli.
Autorhythmic:
An action potential is generated within muscle tissue.
Cardiac muscle is autorhythmic.
Types of cardiac muscle cells:
Contractile cell.
Conducting cell.
Contractile cells:
Generate the force that pumps blood.
Not autorhythmic.
Conducting cells:
Do not generate force.
These cells generate action potentials and rapidly propagate them through muscle tissue.
Some conducting cells are located in two groups:
SA node & the AV node.
Both are located in the right atrium.
SA node lies:
Near the junction with the superior vena cava.
The AV node lies:
Near the right AV valve.
Most conducting cells are organized into:
Bundles or tracts.
What links the SA node to the AV node:
The Atrial internodal tract.
The AV node propagates action potential into the ventricles.
Into the ventricles.
The course of action of a cardiac action potential.
AV node.
Bundle of His (common bundle).
R & L bundle branches.
Purkinje fibers.
* Rapid propagation of action potential.
Propagation of an action potential from the SA node to all other parts of cardiac muscle takes:
220 msec at a resting heart rate.
Propagation between contractile cells occurs at:
1 m/sec.
Propagation between most conducting cells is ____ times faster than contracting cells.
2-4 times faster.
The slow conduction time of the AV node allows:
Atria to contact before the ventricle.
Ventricular bundles:
Large bundles in the intraventricular septum.
Cells in SA node:
Generate an action potential at regular intervals.
Pacemaker potential:
When a cell completes an action potential, it immediately begins a slow depolarization.
The potential between two action potentials in the SA node.
Resting potential:
Membrane potential in the absence of stimulation.
SA node action potential:
No resting potential, unstable membrane potential.
At the end of an action potential, the membrane potential slowly depolarizes.
Two types of ion channels that produce the pacemaker potentials:
F-type channels.
T-type channels.
Both open during the pacemaker potential but close when the membrane potential reaches the threshold again.
F-type channels:
Non-specific cation channels that primarily allow sodium ions to cross the membrane.
Open at the end of an action potential, inward sodium depolarizes the membrane.
They open fast.
T-types channels:
Opens as the membrane potential nears threshold, allowing calcium ions to move in.
This further depolarizes the membrane.
L-type channels:
At threshold, these voltage-gated channels open gradually.
This allows further prolonged inward movement of calcium ions.
They begin to close at the same time the potassium ion opens.
Resets during repolarization.
Potassium ion channels:
Voltage-gated ion channels allow the outward movement of potassium ions which repolarizes the membrane.
They open & close slowly.
Action potential in contracting cells:
The cell has a stable resting potential.
Action potential is divided into 4 phases.
In contractile cells Na & K have: **
2 gates.
In a contractile cell threshold:
All signals get the signal to open.
Plateau phase:
The movement potential does not change.
Outward K+ is the same as inward Ca++.
Phase 0:
It occurs when the membrane is depolarized to threshold.
It is induced when voltage-gated Na ion channels open.
Rapid inward movement of Na ion.
Closes after 1 msec.
Phases 1-3 are :
Repolarization phases.
Phase 1:
Voltage-gated K+ channel 1 opens.
K+ Moves outwards.
Brief rapid repolarization.
The contractile cell action potential has how many phases:
4 phases.
Phases 0-3.
Phase 2:
Voltage-gated L-type calcium ion channels open.
Inward movement of calcium.
Voltage-gated K+ channel 1 is still open.
Plateau phase.
Phase 3:
Both the L-type calcium ion and K+ channel 1 are closed.
A second type of K+ ion opens.
K+ ions move outwards.
Another brief repolarization occurs.
Membrane returns to resting potential.
When does phase 3 end:
When the membrane potential return to resting potential.
