Cardiovascular Physiology Lecture 3 Flashcards
What are the two types of AP’s in the heart?
Fast and slow
Where are fast AP’s found?
Found in contractile myocytes in the atrial myocardium, ventricular myocardium, bundle of His, Bundle branches (left and right) and Purkinje fibres
Where are slow response action potentials found?
Conducting myocytes of the:
- Sinoatrial node
- Atrioventricular node
What do the terms fast and slow refer to in types of action potentials?
How quickly the membrane potential changes during the depolarization phase of the AP
- Fast:
- Rapid rate of depolarization in which the membrane potential rises very quickly from the threshold pot. to the new transiently positive potential
- Slow:
- Slower rate of depolarization, in which the membrane potential take more time to m=reach the new potential
Why do action potentials have different rates of depolarization?
Depends on the ions and ion channels involved in the depolarization phase
Phases of the cardiac AP are associated with changes in the permeability of the cell membrane mainly to which 3 ions?
Na+
K+
Ca2+
What happens during a Cardiac AP in regards to K+, Ca2+ and Na+
[K+] inside cell is higher than outside (will leave cell)
[Ca2+] is higher outside the cell than inside the cell (will enter cell)
[Na+] is higher outside the cell than inside (will enter cell)
What are the 3 phases of a slow action potential (as with the SA node AP)
- Pacemaker potential
- Depolarization
- Repolarization
it is not a steady or true resting potential but a slow depolarization to threshold; gradual depolarization of the membrane potential to threshold
Pacemaker potential
Pacemaker potential allows the SA Nodal cells to generate spontaneous ________
Pacemaker potential allows the SA Nodal cells to generate spontaneous action potentials without any external influence from nerves or hormones
What three ionic conductances are involved with bringing a pacemaker potential to a spontaneous AP?
- Progressive reduction in K+ permeability (K+ channels that opened during the repolarization phase of the previous AP gradually close due tot he return of the membrane to negative potential)
- F-type channels (depolarizing Na+ current; Na+ moves into cell)
- T-Type channels (Ca2+ channels; T=transient; opens only transiently (briefly); contributes to inward Ca2+ current; provides a final depolarization to bring the membrane to threshold)
What is the depolarization phase of a slow action potential?
- L-type channels (Ca2+ channel; L=long lasting; channels open more slowly and remain open for a prolonged period
Why does the rising phase of an action potential occur slower in slow AP?
Ca2+ currents depolarize the membrane more slowly than voltage-gated Na+ channels, so the rising phase occurs slower than if Na+ was responsible (as they are in nerve/muscle AP)
What is the repolarization phase of the slow AP?
Opening of voltage gated K+ channels. K+ leaves the cell
______ _______ of the pacemaker potential allows SA Node to generate AP
Gradual Depolarization of the pacemaker potential allows SA Node to generate AP
In slow AP which ion is responsible for the depolarization phase?
Ca2+ (not Na+)
If the SA node becomes damaged, the ______ may generate Ap’s to drive the ventricles, but at a slower rate (40-60 bpm)
If the SA node becomes damaged, the AV node may generate Ap’s to drive the ventricles, but at a slower rate (40-60 bpm)
Various _____ channels are involved in the resting phase, the notch and the repolarization phase of Ventricular Muscle Cell AP
Various K+ channels are involved in the resting phase, the notch and the repolarization phase of Ventricular Muscle Cell AP
What is the P-wave of an ECG?
- First wave on ECG
- Represents depolarization of the atria
- Upward deflection in the trace
- approximately 25ms after the P-wave the atria will contract
What is the QRS complex?
- Wave consisting of 3 peaks labelled Q, R, and S
- represents depolarization of the ventricles
- When the ventricles are depolarizing, the atria repolarize
Which wave would you see approximated 25ms before the atria contract?
P-wave
What would you see on the ECG if the ventricles were contracting?
QRS complex
What is the T-Wave on the ECG?
- upward deflection
- represents repolarization of the ventricles
What is an AV node block?
Type of heart block in which the conduction between the atria and ventricles is impaired; partial or complete interruption of the impulse from the atria to the ventricles
plasma/cell membrane of a cardiac cell =
sarcolemma
Special type of smooth ER that stores and pumps Ca2+ in the heart:
Sarcoplasmic reticulum
What is the contractile unit of heart muscle (contains filaments actin and myosin)
Sarcomeres (make up myofibrils)
What are invaginations of the sarcolemma that surround myofibrils and transmit AP’s?
T-Tubules
T-Tubules lie in close proximity to the ________ and contain many _______ channels
T-Tubules lie in close proximity to the sarcoplasmic reticulum and contain many L-type Ca2+ channels
What is excitation-contraction coupling?
process by which the arrival of an AP at the cell membrane leads to contraction of the muscle cell
What are the steps involved in ECC (excitation-contraction coupling)
-
__\_ levels control contraction of the cardiac muscle
- normally found in low concentrations in the _____\_and in high concentration sin the ____\_
- During the plateau phase of the AP, extracellular Ca2+ enter the cytoplasm of the cardiac muscle cell through the ______\_
- not enough to cause contraction of myocytes
- Ca2+ that enters binds to _____\_and their channels open allowing release of Ca2+ from the ______ ____\_ into the cytoplasm
What are the steps involved in ECC (excitation-contraction coupling)
-
Ca2+ levels control contraction of the cardiac muscle
- normally found in low concentrations in the cytoplasm of the cell and in high concentration sin the ECF
- During the plateau phase of the AP, extracellular Ca2+ enter the cytoplasm of the cardiac muscle cell through the L-type Ca2+ channels
- not enough to cause contraction of myocytes
- Ca2+ that enters binds to ryanodine receptors and their channels open allowing release of Ca2+ from the sarcoplasmic reticulum into the cytoplasm
How does Ca2+ cause its own release from the sarcoplasmic reticulum?
By binding to the ryanodine receptor = calcium dependent calcium release or calcium-induced calcium release
Excitation spreads along the sarcolemma (plasma membrane) from ventricular myocyte to ventricular myocyte via ______
Excitation spreads down the interior of the myocyte via ______
Excitation spreads along the sarcolemma (plasma membrane) from ventricular myocyte to ventricular myocyte via gap junctions
Excitation spreads down the interior of the myocyte via t-tubules
What are L-Type calcium channels?
voltage gated Ca2+ channels
Type of modified Dihydropyridine (DHP) receptor
Why is diastole (ventricle relaxation) important?
Because ventricles only fill with blood when they are relaxed
How is a contraction ended in Cardiac muscle?
Must reduce Ca2+ levels:
- _____ channels close to reduce influx of Ca2+ into the cell
- SR no longer stimulated to release Ca2+ into cytoplasm as Ca2+ is not longer entering to bind to _____
- SR contains _____ to pump Ca2+ in the cytosol back into the Sr
- Ca2+ is removed form the myocyte by a _____ in the sarcolemma
Must reduce Ca2+ levels:
- L-type ca2+ channels close to reduce influx of Ca2+ into the cell
- SR no longer stimulated to release Ca2+ into cytoplasm as Ca2+ is not longer entering to bind to ryanodine
- SR contains Ca2+ ATPases to pump Ca2+ in the cytosol back into the Sr
- Ca2+ is removed form the myocyte by a Na+/Ca2+ exchanger in the sarcolemma
