Cardiovascular Physiology Lecture 3

Question 1

What are the two types of AP’s in the heart?

Answer 1

Fast and slow

Question 2

Where are fast AP’s found?

Answer 2

Found in contractile myocytes in the atrial myocardium, ventricular myocardium, bundle of His, Bundle branches (left and right) and Purkinje fibres

Question 3

Where are slow response action potentials found?

Answer 3

Conducting myocytes of the:

• Sinoatrial node
• Atrioventricular node

Question 4

What do the terms fast and slow refer to in types of action potentials?

Answer 4

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

Question 5

Why do action potentials have different rates of depolarization?

Answer 5

Depends on the ions and ion channels involved in the depolarization phase

Question 6

Phases of the cardiac AP are associated with changes in the permeability of the cell membrane mainly to which 3 ions?

Answer 6

Na+

K+

Ca2+

Question 7

What happens during a Cardiac AP in regards to K+, Ca2+ and Na+

Answer 7

[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)

Question 8

What are the 3 phases of a slow action potential (as with the SA node AP)

Answer 8

1. Pacemaker potential
2. Depolarization
3. Repolarization

Question 9

it is not a steady or true resting potential but a slow depolarization to threshold; gradual depolarization of the membrane potential to threshold

Answer 9

Pacemaker potential

Question 10

Pacemaker potential allows the SA Nodal cells to generate spontaneous ________

Answer 10

Pacemaker potential allows the SA Nodal cells to generate spontaneous action potentials without any external influence from nerves or hormones

Question 11

What three ionic conductances are involved with bringing a pacemaker potential to a spontaneous AP?

Answer 11

1. 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)
2. F-type channels (depolarizing Na+ current; Na+ moves into cell)
3. 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)

Question 12

What is the depolarization phase of a slow action potential?

Answer 12

• L-type channels (Ca2+ channel; L=long lasting; channels open more slowly and remain open for a prolonged period

Question 13

Why does the rising phase of an action potential occur slower in slow AP?

Answer 13

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)

Question 14

What is the repolarization phase of the slow AP?

Answer 14

Opening of voltage gated K+ channels. K+ leaves the cell

Question 15

______ _______ of the pacemaker potential allows SA Node to generate AP

Answer 15

Gradual Depolarization of the pacemaker potential allows SA Node to generate AP

Question 16

In slow AP which ion is responsible for the depolarization phase?

Answer 16

Ca2+ (not Na+)

Question 17

If the SA node becomes damaged, the ______ may generate Ap’s to drive the ventricles, but at a slower rate (40-60 bpm)

Answer 17

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)

Question 18

Various _____ channels are involved in the resting phase, the notch and the repolarization phase of Ventricular Muscle Cell AP

Answer 18

Various K+ channels are involved in the resting phase, the notch and the repolarization phase of Ventricular Muscle Cell AP

Question 19

What is the P-wave of an ECG?

Answer 19

• First wave on ECG
• Represents depolarization of the atria
• Upward deflection in the trace
• approximately 25ms after the P-wave the atria will contract

Question 20

What is the QRS complex?

Answer 20

• Wave consisting of 3 peaks labelled Q, R, and S
• represents depolarization of the ventricles
• When the ventricles are depolarizing, the atria repolarize

Question 21

Which wave would you see approximated 25ms before the atria contract?

Answer 21

P-wave

Question 22

What would you see on the ECG if the ventricles were contracting?

Answer 22

QRS complex

Question 23

What is the T-Wave on the ECG?

Answer 23

• upward deflection
• represents repolarization of the ventricles

Question 24

What is an AV node block?

Answer 24

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

Question 25

plasma/cell membrane of a cardiac cell =

Answer 25

sarcolemma

Question 26

Special type of smooth ER that stores and pumps Ca2+ in the heart:

Answer 26

Sarcoplasmic reticulum

Question 27

What is the contractile unit of heart muscle (contains filaments actin and myosin)

Answer 27

Sarcomeres (make up myofibrils)

Question 28

What are invaginations of the sarcolemma that surround myofibrils and transmit AP’s?

Answer 28

T-Tubules

Question 29

T-Tubules lie in close proximity to the ________ and contain many _______ channels

Answer 29

T-Tubules lie in close proximity to the sarcoplasmic reticulum and contain many L-type Ca2+ channels

Question 30

What is excitation-contraction coupling?

Answer 30

process by which the arrival of an AP at the cell membrane leads to contraction of the muscle cell

Question 31

What are the steps involved in ECC (excitation-contraction coupling)

1. __\_ 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

Answer 31

What are the steps involved in ECC (excitation-contraction coupling)

1. 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

Question 32

How does Ca2+ cause its own release from the sarcoplasmic reticulum?

Answer 32

By binding to the ryanodine receptor = calcium dependent calcium release or calcium-induced calcium release

Question 33

Excitation spreads along the sarcolemma (plasma membrane) from ventricular myocyte to ventricular myocyte via ______

Excitation spreads down the interior of the myocyte via ______

Answer 33

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

Question 34

What are L-Type calcium channels?

Answer 34

voltage gated Ca2+ channels

Type of modified Dihydropyridine (DHP) receptor

Question 35

Why is diastole (ventricle relaxation) important?

Answer 35

Because ventricles only fill with blood when they are relaxed

Question 36

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

Answer 36

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