Cardio 1D

Question 1

Where do the non-pacemaker or “Fast Response” action potentials occur?

Answer 1

Atria, ventricles, Purkinje fibers: “Rapid” depolarization

Question 2

Where do the pacemaker of “Slow Response” action potentials occur?

Answer 2

SA node and AV node: “Slow” depolarization

Question 3

What happens in phase 0 rapid depolarization?

Answer 3

• Upstroke of the AP
• “Fast” Na channels open
• Several types of K channels closed

Question 4

What happens in phase 1 early/initial repolarization of non-pacemaker Fast Action Potential?

Answer 4

• Transient outward current as K channels open

- Fast Na channels are closed

Question 5

What happens in phase 2 plateau phase of non-pacemaker Fast Action Potential ?

Answer 5

• Long lasting (L-type) Ca channels open leading to inward calcium movement
• Efflux of K through several types of K channels

Question 6

What is the key difference between the excitability of cardiac muscle cells and skeletal muscle cells?

Answer 6

Cardiac contraction has an absolute requirement for Ca influx through L-type channels where skeletal muscle doesn’t

Question 7

Does the amount of calcium entering the cardiac muscle cell during an action potential promote actin-myosin binding?

Answer 7

NO

Question 8

What is the effect of the influx of calcium into the cell during an action potential?

Answer 8

Induces calcium release from the sarcoplasmic reticulum

Question 9

What does CICR stand for? And what does it produce?

Answer 9

Calcium-induced Calcium Release promotes actin-myosin interaction and hence contraction

Question 10

What does the ryanodine receptor do? (RyR2)?

Answer 10

Help with muscle contraction

Question 11

What increases calcium conductance?

Answer 11

NE, Sympathetic Nervous System and Adrenal Glands

Question 12

What decreases calcium conductance?

Answer 12

Ach, Beta blockers, and Ca channel blockers

Question 13

What happens in phase 3 Late or Final Repolarization of non-pacemaker Fast Action Potential?

Answer 13

Continual efflux of potassium (K) through several types of K channels, L-type Ca channels eventually close

Question 14

What happens in phase 4 (RMP) of non-pacemaker Fast Action Potential?

Answer 14

K channels remain open, calcium extrusion mechanisms become highly active

Question 15

What are the three means of calcium extrusion?

Answer 15

SR pumps (SERCA), Sarcolemma Ca pumps, Sodium Calcium Exchangers (NCX)

Question 16

Do the mechanical and electrical events in cardiac muscle overlap?

Answer 16

YES

Question 17

What is the result of the overlap of mechanical and electrical events in cardiac muscle?

Answer 17

It makes it impossible to produce the summation and tetanus found in skeletal muscles during high frequency stimulation in cardiac muscles

Question 18

What is the effective or absolute refractory period?

Answer 18

The time needed for repolarization where another action potential cannot be initiated no matter how large the stimulus is that is applied

Question 19

What is the relative refractory period?

Answer 19

Another action potential may be evoked only when the stimulus is sufficiently strong (suprathreshhold)

Question 20

What is the normal pacemaker of the heart?

Answer 20

The SA node

Question 21

What is significant about the pacemaker of the heart?

Answer 21

• Has an unstable resting membrane potential

- Exhibits phase 4 depolarization or automaticity (the ability to initiate its own depolarization)

Question 22

What happens in phase 0 of the pace maker/ slow action potential?

Answer 22

• Upstroke of the AP

- Caused by an increase in Ca conductance

Question 23

What is an important difference between the slow and fast response action potentials?

Answer 23

-Slow are initiated by calcium and fast are initiated by sodium

Question 24

What happens in phase 3 of the pacemaker/ slow action potential?

Answer 24

• Repolarization

- Increase in K outward conductance

Question 25

What occurs in phase 4 of the pacemaker / slow action potential?

Answer 25

- Slow depolarization - Accounts for the pacemaker activity of the SA node (automaticity) - Caused by an increase in Na conductance which is results in a n inward current called If

Question 26

How is If turned on?

Answer 26

By repolarization of the membrane potential during the preceding action potential

Question 27

What is the term for the number of times the SA node discharges per minute?

Answer 27

Heart rate

Question 28

What is conduction velocity?

Answer 28

The time required for excitation to spread throughout cardiac tissue

Question 29

Where is conduction velocity the fastest?

Answer 29

Purkinje system

Question 30

Where is conduction velocity the slowest?

Answer 30

AV node

Question 31

What does a chronotropic effect do?

Answer 31

Produce change in HR Negative chronotropic effect decreases HR by decreasing firing rate of SA node and positive chonotropic effect increases HR by increasing firing rate of SA node

Question 32

What is dromotropic effect?

Answer 32

Changes conduction velocity in the AV node. Negative dromotropic effect decreases conduction velocity through AV node. Positive dromotropic effect increases conduction velocity through AV node.

Question 33

What parts of the heart have parasympathetic innervation?

Answer 33

SA node, atria, and AV node. VENTRICLES DO NOT!!!

Question 34

What is the neurotransmitter for the parasympathetic stimulation of the heart?

Answer 34

Ach Acetylcholine (acts at muscarinic receptors)

Question 35

What parts of the heart have sympathetic innervation?

Answer 35

SA node, AV node, atria, and ventricles

Question 36

What is the neurotransmitter for the sympathetic innervation?

Answer 36

Norepinephrine (acts on beta 1 receptors)

Question 37

What does chronotropic effect affect?

Answer 37

Heart rate

Question 38

What does dromotropic effect affect?

Answer 38

Conduction velocity