Ventricular Muscle

Question 1

What is cardiac muscle contraction triggered by?

Answer 1

Action potential at the sarcolemma

Question 2

Where does the electrical excitation occur?

Answer 2

Sinoatrial node

Question 3

At rest, is the inside of the plasma membrane negative or positive with respect to the outside?

Answer 3

negative

Question 4

What sets up the membrane potential?

Answer 4

Uneven distribution of ions

Question 5

What ions are the main ions in the modulation of membrane potential in cardiac myocytes?

Answer 5

Ca2+, K+ and Na+ ions

Question 6

What happens when channels open?

Answer 6

Ions flow down their concentration gradient

Question 7

What happens at rest with K+?

Answer 7

K+ leaks out through Kir channels
Generating current iKir/iK1 (- 80mV)

Question 8

What causes the depolarization in electrical activity?

Answer 8

Na+ influx

Question 9

What causes the plateau in electrical activity?

Answer 9

Ca2+ influx

Question 10

What causes the repolarization in electrical activity?

Answer 10

K+ influx

Question 11

What is the refractory period?

Answer 11

No summation of contractions.

Question 12

What does the refractory period permit?

Answer 12

Filling of the ventricles between contractions

Question 13

Describe what happens in phase 0 of ventricular AP?

Answer 13

AP reaches adjacent myocyte
depolarization begins
overshoot generated
sodium channels open and inactivate rapidly
closure occurs as repolarization progresses

Question 14

Describe what happens in phase 1 of ventricular AP?

Answer 14

Brief repolarization caused by Ito through K+ channels
Activated and inactivated quickly

Question 15

Describe what happens in phase 2 of ventricular AP?

Answer 15

Plateau period with iCa through L-type Ca2+ channels
Reduced iKir

Question 16

Describe what happens in phase 3 of ventricular AP?

Answer 16

K+ efflux increases through Kv channels

Question 17

Describe what happens in phase 4 of ventricular AP?

Answer 17

Kir reopen to complete repolarization
Kv close when resting Vm is reached
Resting Vm re-established
Ca2+ pumped back to SR via Ca2+-ATPase
Remainder extruded by 3Na+/Ca2+ exchangers
ib reduces Vm (less negative)

Question 18

What stimulates cardiac myocytes?

Answer 18

Adrenergic stimulation which increases iCa which increases contractility

Question 19

What shortens the AP?

Answer 19

Sympathetic stimulation - repolarization occurs sooner
shorter duration = more APs per min

Question 20

Define arrhythmias?

Answer 20

Abnormalities in electrical conductance which causes HR or cardiac rhythm disturbances

Question 21

What shortens AP duration due to KATP opening?

Answer 21

Hypoxia

Question 22

What can lengthen the plateau period?

Answer 22

Certain mutations to channel protein variants?

Question 23

How are arrhythmias treated?

Answer 23

Block sodium channels
blocked sympathetic nerve activity
prolong refractory period
block calcium channels