hjärtfysiologi ii

Question 1

which part of the heart supplies the main pumping force?

Answer 1

the ventricles (atriums are weak, moving blood into the ventricles.

Question 2

which are the three major types of cardiac muscle?

Answer 2

1. atrial
2. ventricular
3. conductive/excitatory

Question 3

the cardiac muscle is a syncitium. what does that mean?

Answer 3

the cardiac cells are so interconnected that when one cell becomes excited, the action
potential rapidly spreads to all of them.

Question 4

what’s the amplitude of the action potential in the ventricular muscle?

Answer 4

between -85 and +20 millivolts.

Question 5

what causes the plateau that makes the action potential in cardiac muscle much longer than in skeletal muscle?

Answer 5

it is due to the slower l-type calcium channels, which maintain a prolonged period of depolarization.

Question 6

how is the action potential initiated in the cardiac muscle?

Answer 6

1) voltage activated natrium channels (fast)
2) l-type calcium channels (slow)

Question 7

describe the phases of cardiac muscle action potential.

Answer 7

phase 0 (depolarization): fast natrium channels open.

phase 1 (initial repolarization): fast natrium channels close, kalium leaves through open channels.

phase 2 (plateau): calcium channels open and fast kalium channels close.

phase 3 (rapid repolarization): calcium channelse close and slow kalium channels open.

phase 4 (resting membrane potential): around -80 millivolts, determined by kalium “leakage” channels.

Question 8

what is the velocity of conduction in the atrial and ventricular muscle fibers? how about the purkinje fibers?

Answer 8

atrial/ventricular: 0,5 m/s
purkinje: 4 m/s

Question 9

during the refractory period…

Answer 9

… a normal cardiac impulse cannot re-excite an already excited area of cardiac muscle.

Question 10

how is contraction achieved in the heart muscle fiber?

Answer 10

1. calcium enters the t-tubules and opens l-type calcium channels
2. release of calcium ions into the cytoplasm
3. calcium activates ryanodine receptor channels on the sr
4. release of calcium ions from the sarcoplasmatic reticulum
5. calcium interacts with troponin to initiate contraction

Question 11

what happens at the end of the plateau?

Answer 11

1) calcium influx is cut off,
2) calcium ions in the cytoplasm are pumped back into the SR via SERCA,
3) calcium ions are removed from the cell by a natrium-calcium exchanger.

Question 12

each cardiac cycle is initiated by…

Answer 12

the spontaneous generation of an action potential in the sinus node.

Question 13

when heart rate increases, the duration of each cardiac cycle…

Answer 13

decreases (including the contraction and relaxation phases).

Question 14

what causes the P wave on an EKG?

Answer 14

the spread of depolarization
through the atria.

Question 15

what does the QRS complex show?

Answer 15

depolarization of the ventricles, which initiates contraction of the ventricles.

Question 16

what does the T wave show?

Answer 16

repolarisation of the ventricles, which occurs slightly before the end of ventricular contraction.