Origin & conduction of cardiac impulse

Question 1

Generation of electrical signals which control heart?

Answer 1

Within heart

Question 2

Autorhythmicity?

Answer 2

Heart is capable of beating rhythmically in absence of external stimuli

Question 3

Excitation of heart normally originates where?

Answer 3

In pacemaker cells in SA node

Question 4

Heart driven by SA node is in?

Answer 4

Sinus rythum

Question 5

Where is SA node located?

Answer 5

In upper right atrium close to where superior vena cava enters right atrium

Question 6

How does cardiac excitation normally originate?

Answer 6

Cells in SA node generate reg spontaneous pacemaker potentials which take membrane potential to a threshold and every time this is reached an action potential is generated resulting in reg spontaneous action potentials in SA nodal cells

Question 7

Action potentials?

Answer 7

Transient depolarization of cell followed by repolarization due to ion movement across cell membrane via ion channels

Question 8

Pacemaker potential?

Answer 8

Slow depolarization of membrane potential to a threshold

Question 9

Pacemaker potential is due to?

Answer 9

Dec in K+ efflux
Na+ influx (funny current
Transient Ca++ influx (T-type Ca++ channels)

Question 10

What causes rising phase of action potential (depolarization)?

Answer 10

Activation of long lasting (L-type) Ca++ channels resulting in Ca++ influx

Question 11

What causes falling phase of action potential (repolarization)?

Answer 11

Inactivation of L-type CA++ channels resulting in K+ efflux

Question 12

Action potential?

Answer 12

Change in voltage that occurs across membrane of nerve or muscle cell when nerve impulse is triggered due to passive of charged particles across membrane

Question 13

Depolarization?

Answer 13

Sudden surge of charged particles across membrane that accompanies a physicochemical change and cancels out / reverses resting potential to produce action potential

Question 14

Repolarization?

Answer 14

Membrane of nerve cell returns to normal electrically charged state after nerve impulse has passed

Question 15

Only part of electrical contact between atria and ventricles?

Answer 15

AV node

Question 16

AV node?

Answer 16

Small bundle specialised cells at base of RA

Question 17

Spread of excitation across atria?

Answer 17

Mainly cell-to-cell conduction via gap junctions

Question 18

Spread of excitation from SA node to AV node

Answer 18

Mainly cell-to-cell conduction via gap junctions

Question 19

Delay of conduction in AV node?

Answer 19

Allows atrial systole to precede ventricular systole

Question 20

Bundle of His and branches and Purkinje fibres allow?

Answer 20

Rapid spread of action potential to ventricles

Question 21

Spread of excitation in ventricular muscle?

Answer 21

Cell-to-cell conduction