Physiological properties of the heart

Question 1

What is a syncitium?

Answer 1

A multinucleated cell

Question 2

What percentage of cardiac fibres do not contract?

Answer 2

1%

Question 3

What is the effect of the parasympathetic nervous system on the rate of SA node depolarisation?

Answer 3

Decreases rate of SA node depolarisation

Question 4

What is the effect of the sympathetic nervous system on the rate of SA node depolarisation?

Answer 4

Increases rate of SA node depolarisation

Question 5

What is the intrinsic pacemaker of the heart?

Answer 5

The Sinoatrial node

Question 6

How long is the cardiac cycle roughly?

Answer 6

0.6 - 1 second

Question 7

What is the resting potential of cardiac muscle?

Answer 7

Roughly -90 mV

Question 8

What is the ratio of K+ to Na+ inside the cell?

Answer 8

K+ exceeds Na+ by 50:1

Question 9

What is the effect of sympathetic stimulation affect on cyclic AMP production?

Answer 9

Increases cAMP production

Question 10

Sympathetic stimulation increases what ion concentrations?

Answer 10

Ca2+ and Na+ (Na+ via ‘funny’ channels)

Question 11

What is a positive chronotropic effect?

Answer 11

An increase in heart rate

Question 12

What is a positive ionotropic effect?

Answer 12

Increase the strength of muscular contraction (stroke volume)

Question 13

What does phase 0 of ventricular depolarisation involve?

Answer 13

Rapid depolarisation due to an increase in Na+ permeability as fast Na+ channels open

Question 14

What does phase 1 of ventricular depolarisation involve?

Answer 14

Start of repolarisation as fast Na+ channels close

Question 15

What does phase 2 of ventricular depolarisation involve?

Answer 15

Effect of Ca2+ entry via L-type [DHP] channels

Question 16

What does phase 3 of ventricular depolarisation involve?

Answer 16

Rapid repolarisation as increase Ca2+ concentration stimulates K+ channels to open and increase K+ permeability

Question 17

What does phase 4 of ventricular depolarisation involve?

Answer 17

Stable resting membrane potential where K+ exceeds Na+ by 50:1

Question 18

Symapthetic stimulation effects what type of receptor?

Answer 18

NA acts on B1 recptors to increase cAMP production

Question 19

Parasympathetic stimulation effects what type of receptor?

Answer 19

Ach acts of M2 receptors which decrease cAMP production

Question 20

Parasympathetic stimulation affect on membrane potential?

Answer 20

Hyperpolarises membrane potential to lower starting level.

Question 21

Parasympathetic stimulation increases what ion concentration?

Answer 21

K+ concentration increases due to an increase in extent and duration of opening of K+ channels

Question 22

An increase in Ca2+ causes an increase in what?

Answer 22

stroke volume

Question 23

An increase in Na+ causes an increase in what?

Answer 23

Heart rate

Question 24

What is Einthoven’s triangle?

Answer 24

Einthoven’s triangle is an imaginary formation of three limb leads in a triangle used in electrocardiography, formed by the two shoulders and the pubis.The shape forms an inverted equilateral triangle with the heart at the center that produces zero potential when the voltages are summed.

Question 25

What is the rate of depolarisation of the SA node?

Answer 25

90/min

Question 26

What is the rate of depolarisation of the AV node?

Answer 26

60/min

Question 27

What is the rate of depolarisation of the bundle of His?

Answer 27

50/min

Question 28

What is the rate of depolarisation of the purkinje fibres?

Answer 28

40/min

Question 29

What is the rate of depolarisation of the ventricles?

Answer 29

30/min