Electro

Question 1

Describe Phase 0 of Cardiac Action potential

Answer 1

• DEPOLARIZATION (VERY FAST)
• Fast due to opening of SODIUM CHANNELS
• High conc outside vs inside (allowing influx of sodium into cell)

Question 2

Describe Phase I of Cardiac action potential

Answer 2

Early REPOLARIZATION (SLIGHT repolarization)

Sodium channels close, but SOME potassium channels open

Repolarization INCOMPLETE

Due to opening of Ca+

Question 3

describe Phase II of Cardiac action potential

Answer 3

Plateau**

Membrane potential = 0mv
Due to slow Ca+ channels

Causes calcium to enter the cell leading to no NET current (balance between Ca and K)

Requires concurrent movement opposite to calcium
Allows blood to be ejected from heart

Question 4

Describe Phase III of Cardiac action potential

Answer 4

Rapid repolarization

More calcium channels are closing, and more opening of potassium channels lead to shift in current

Question 5

Describe phase IV of Cardiac action potential

Answer 5

Resting membrane potential (-90mv)

Only POTASSIUM channels are open

Resting potential maintained until next stimulus

Question 6

describe Phase 0 of Nodal Tissue

Answer 6

(resting potential = -60mv)

Once threshold potential (-40mv)is met, calcium channels OPEN

-NO Na+ channels

Leads to SLOWER DEPOLARIZATION –> Ca+ open slower (slower kinetics)

Question 7

Describe Phase 3 of Nodal tissue

Answer 7

After depolarization, potassium channels open

Leads to repolarization

Question 8

describe phase 4 of nodal tissue

Answer 8

FUNNY CURRENT slowly depolarizes cells

Progressive reduction in potassium efflux (less positive charge moving out)

Progressive increase in calcium influx (more positive charge moving in)

Question 9

describe the sequence of depolarization of cardiac tissue

Answer 9

1) SA node (SA and AV have slower conduction velocity to allow mechanical events to take place)
2) Atria
3) AV node
4) Bundle of His
5) Bundle branches
6) Purkinje fibers
7) Ventricle (Septum –> Apex –> Free ventricular walls)

Question 10

Define P wave

Answer 10

• Atrial myocyte depolarization (Phase 0)

Question 11

describe T wave

Answer 11

• Ventricular myocyte repolarization (phase 3)

Question 12

Describe QRS complex

Answer 12

• ventricular myocyte depolarizations (phase 0)

Question 13

what could be the effect if P wave is absent

Answer 13

No atrial depolarization (SA node)

Question 14

What is the indication if lack of QRS after each P wave

Answer 14

• ventricular depolarization doesn’t always occur after atrial depolarization