Conduction

Question 1

What is autorhythmicity of the heart?

Answer 1

the heart is capable of beating regularly without external factors

Question 2

What drives the sinus rhythm of the heart?

Answer 2

SA node

Question 3

Do pacemaker cells of the sinoatrial node have a stable membrane potential? what does this allow for?

Answer 3

no

generation of an action potential

Question 4

What changes the membrane potential?

Answer 4

movement of ions

Question 5

What is depolarization?

Answer 5

the membrane potential becomes less negative or even positive

Question 6

What is hyperpolarization?

Answer 6

the membrane becomes more negative

Question 7

What is the resting potential of a pacemaker cell?

Answer 7

• 70 mV

Question 8

What drives the passive movement of an ion through an ion channel?

Answer 8

the electrochemical gradient

Question 9

What is pacemaker potential?

Answer 9

rising depolarisation to the threshold

Question 10

What causes pacemaker potential?

Answer 10

funny currents that allow slow influx of sodium

decreased K+ Efflux
Na+ and K+ influx
transient Ca+ influx

Question 11

Are voltage-gated Na+ channels hyperpolarising or depolarising?

Answer 11

depolarising

Question 12

Are voltage-gated K+ channels hyperpolarising or depolarising?

Answer 12

hyperpolarizing

Question 13

Which direction does 
a) sodium
b) calcium
b) potassium
tend to flow?

Answer 13

a) in to cell
b) in to cell
c) out of cell

Question 14

What causes the rising phase of depolarisation in a pacemaker cell?

Answer 14

activation of long lasting, L type Ca+ channels causes calcium influx

Question 15

What causes repolarisation in a pacemaker cell?

Answer 15

inactivation of L type Ca+ channels

activation of K+ channels causing K+ efflux

Question 16

At what membrane potential, do sodium channels become inactive and potassium channels open in a pacemaker cell?

Answer 16

+ 40 mV

Question 17

Which type of transport in a pacemaker cell gets the membrane potential from

a) resting to threshold?
b) threshold to +40?

Answer 17

a) mechanic sodium channels

b) voltage-activated sodium channels

Question 18

Is sodium or potassium conductance earlier on, greater and more short-lived?

Answer 18

sodium

Question 19

What are action potentials?

Answer 19

brief electrical signals in which the polarity of the nerve cell membrane is momentarily reversed

Question 20

What is the magnitude and velocity of an action potential determined by?

Answer 20

it is constant for a given axon

all or none, either there or not

Question 21

What activates voltage-gated channels?

Answer 21

depolarization

Question 22

Do voltage-activated calcium channels activate with positive or negative reinforcement?

Answer 22

positive: opening of a few channels stimulates others

Question 23

Do voltage-activated potassium channels activate with positive or negative reinforcement?

Answer 23

negative: outward movement of potassium repolarizes the cell which turns off the channels

Question 24

What is the refractory period?

Answer 24

when a voltage-activated sodium channel enters an inactive state during maintained depolarisation, it requires to be repolarized before another AP can occur

Question 25

What does the refractory period do?

Answer 25

it limits the frequency at which any nerve fibre can fire an action potential

Question 26

What is the relationship between diameter of axon and resistance to current flow?

Answer 26

the bigger the diameter of axon, the less resistance to current flow

Question 27

How does conduction spread across the atria?

Answer 27

cell to cell via gap junctions

Question 28

What happens to conduction in the AV node? what does this allow?

Answer 28

delayed allows atrial systole (contraction) to precede ventricular systole

Question 29

What allows for rapid spread of action potential to the ventricles?

Answer 29

The Bundle of His and its branches and the network of Purkinje fibers

Question 30

What is the resting potential for a cardiac myocyte?

Answer 30

- 90 mV

Question 31

What causes phase 0 of a cardiac myocyte action potential?

Answer 31

fast Na+ influx causes depolarisation

Question 32

What causes phase 1 of a cardiac myocyte action potential?

Answer 32

Closure of Na+ channels and Transient K+ efflux

Question 33

What causes phase 3 of a cardiac myocyte action potential?

Answer 33

Closure of Ca++ channels and K+ efflux

Question 34

What is phase 4 of a cardiac myocyte action potential?

Answer 34

resting potential

Question 35

What causes the plateau in cardiac myocyte action potential?

Answer 35

Influx of Ca++ through L-type Ca++ channels

Question 36

How does the vagus nerve slow the heart rate?

Answer 36

Using AcH acting through muscarinic m2 receptors

Question 37

What competes with AcH to inhibit the vagus nerve from slowing HR?

Answer 37

atropine

Question 38

What effect does an agent that slows the heart rate have?

Answer 38

negative chronotropic effect

Question 39

What does a negative chronotropic effect mean for a) slope of pacemaker potential b) frequency of AP?

Answer 39

a) decreases | b) decreases

Question 40

What effect does an agent that speeds up the heart rate have?

Answer 40

positive chronotropic effect

Question 41

What does a positive chronotropic effect mean for a) slope of pacemaker potential b) frequency of AP?

Answer 41

a) increases | b) increases

Question 42

What does sympathetic supply have on a) pacemaker cell K+ efflux? b) pacemaker cell Na+ and Ca++ influx?

Answer 42

a) decrease | b) increase

Question 43

What does parasympathetic supply have on a) pacemaker cell K+ efflux? b) pacemaker cell Na+ and Ca++ influx?

Answer 43

a) increase | b) decrease