Electric activity of the heart, electromechanical coupling

Question 1

what are the 3 excitable tissues

Answer 1

working muscle fibers, pacemaker cells and conduction fibers

Question 2

what do working fibres do

Answer 2

Working fibers: generate unique, elongated AP(plateau), which prevents the heart from early secondary contraction.

Question 3

what does pacemakers cells do

Answer 3

. Pacemakers: has no permanent resting membrane potential, but turns into constant depolarization (lifetime pacemaker)

Question 4

what does conductive fibre do

Answer 4

Conductive system provides rapid spreading of stimuli, hence providing synchronized contraction between atria and ventricles.

Question 5

Position of the action potential in the heart compared to the plateau phase

Answer 5

An action potential of cells closer to the base and to the endocardium exhibit a longer plateau phase, than that of those situated in the vicinity of the apex and the epicardium. This influences the final picture of the total electrical activity of the heart.

Question 6

Average resting membrane potential

Answer 6

Average resting membrane potential is -90 mV.

Question 7

The fiber is stimulated by what and does occurs due to it

Answer 7

The fiber is stimulated by an electrical impulse so that the RMP shifts towards and reaches the threshold potential.

Question 8

how do you reach the threshold potential

Answer 8

the voltage sensitive fast sodium channels open and a sudden influx of the sodium from the EC occur. With this change one enters the so- called 0. phase of the AP.

Question 9

o. phase

Answer 9

depolarization: Influx of sodium continues, membrane potential reaches approximately +25 mV.
Na* Ions go into the sarcoplasmic retuculum

Question 10

1. phase

Answer 10

overshoot: Depolarization is stopped. Repolarization begins. Short chloride influx and potassium efflux (K+ ions go outside of cell)

Question 11

2. phase

Answer 11

– plateau: Calcium channels open, calcium influx. At the same time potassium channels open, potassium efflux. The balance of these processes causes the elongation of this phase.
(k+ (out) and Ca+ (in) ions go in and out at the same quantity so it reaches equilibrium).

Question 12

3. phase

Answer 12

– full repolarization: The late potassium channels open and potassium rapidly flows out of the cell according to its electrochemical gradient, while the calcium channels close.
(K+ ions go out)

Question 13

all phases name

Answer 13

0. phase - depolarization
1. phase – overshoot:
2. phase – plateau:
3. phase – full repolarization:

Question 14

After (during) contraction of electromechanical cupling

Answer 14

ATP-dependent Ca pump drives back the Ca to the SR, plus Na/Ca antiport pumps back the Ca to EC space – IC Ca conc. Drops - resulting in relaxation.