Electrical Activity

Question 1

Define depolarisation

Answer 1

Cell becomes less polarised. The inside of cell is less negative than normal

Question 2

How do pacemaker cells / autorhythmic cells generate action potentials spontaneously?

Answer 2

Because it has an unstable resting membrane potential.

Question 3

Which two ion channels are responsible for the unstable resting membrane potential of authorhythmic cells? Describe the movement of ions.

Answer 3

Funny channels = slow entry of Na into cell (causes depolarisation)
T type calcium channels = transient calcium influx

Question 4

Which ion is higher in concentration outside the cell compared to inside? Calcium, potassium or sodium?

Answer 4

Sodium and calcium. K is more concentrated inside

Question 5

When do the funny channels close?

Answer 5

Half way through the pacemaker potential. Once closed, T-type calcium channels open, which allows for further depolarisation until the threshold is reached.

Question 6

Which ion and ion channel is responsible for the rapid depolarisation of autorhythmic cells?

Answer 6

L-type calcium channels open, allowing for large influx of calcium.

Question 7

Which ion and ion channel are responsible for the repolarisation of autorhythmic cells?

Answer 7

At peak of depolarisation, voltage gated K channels open, allowing for large K efflux

Question 8

Which ion channel maintains the stable resting membrane potential of contractile cells?

Answer 8

A leaky K channel. Slow K efflux

Question 9

Once the flow of current arrives via gap junctions, what causes the depolarisation of contractile cells?

Answer 9

Voltage gated Na channels = rapid Na influx

Question 10

Explain the two ion channels contributing to the plateau of the contractile cell’s action potential

Answer 10

Transient K channels open, allowIng quick but brief K efflux. Causes slight repolarisation, then channel closes
L-type Ca channels open, allowimg slow Ca influx, which prolongs the peak of thr action potential

Question 11

What causes the repolarisation of contractile cells?

Answer 11

L-type calcium channels close, causing voltage gated K channels to open. Fast K efflux repolarises cell

Question 12

Primary, secondary and tertiary pacemaker of heart?

Answer 12

SA node
AV node
Purkinje fibres

Question 13

What happens when damage to AV node causes purkinje fibres to become primary pacemaker?

Answer 13

Complete heart block.
Caused by no electrical signal tranduction between atria and ventricles
Purkinje fibre AP rate is also far too slow

Question 14

Define an ectopic focus

Answer 14

When purkinje fibres become faster than SA node. Causes premature heart beats and PVC

Question 15

Define PVC

Answer 15

Premature ventricular contraction

= less blood ejected

Question 16

Causes of ectopic focus?

Answer 16

Alcohol, nicotine, stress, caffiene, anxiety, etc

Question 17

What is the major connection between atria and ventricles?

Answer 17

AV node

Question 18

Why is there a delay of transduction at the AV node?

Answer 18

To allow the atria to finish contracting before the ventricles start

Question 19

Why is the refractory period of a cardiomyocyte longer than regular muscle cells?

Answer 19

To ensure each contraction is followed by enough time to ensure the chambers refill before the next contraction. Prevents tetanus contractions

Question 20

Where does the electrical signal travel after SA node and AV node?

Answer 20

Bundle of his, then apex of ventricle

Question 21

After the electrical signal reaches the ventricle apex, where does it go?

Answer 21

To the purkinje fibres, then to the rest of the ventricle

Question 22

P wave of ECG =?

Answer 22

Atrial depolarisation + contraction

Question 23

QRS complex =?

Answer 23

Venctricular depolarisation + contraction + simultaneous repolarisation of atria

Question 24

T wave =?

Answer 24

Ventricular relaxation + repolarisation

Question 25

What would ventricle fibrillation look like on ECG?

Answer 25

Rapid, disorganised and irregular signals

Question 26

Describe atrial flutters

Answer 26

Increased rate of atrial contractions. Doesnt allow for ventricles to fill properly. Ventricles will not contract with every atrial contraction (e.g. 3:1)

Question 27

Describe complete heart block

Answer 27

AV node impairment, resulting in ventricles not being stimulated. The atria will contract normally, but the ventricles will generate their own pulses that are much slower than atria pulses / contractions.

Question 28

Complete heart block appearance on ecg?

Answer 28

Normal P wave (due to normal atrial contractions)
Slow QRS and T waves (slow, but still regular)
Extra lines may appear which represent atrial repolarisation (normally masked by QRS complex, but they are no longer simultaneous)

Question 29

PSNS effect on ions and HR?

Answer 29

Opens K channels, causing hyperpolarisation, meaning takes longer to reach threshold. = slower HR

Question 30

SNS effect on HR and ions?

Answer 30

Increases closure of K channels, meaning threshold is reached sooner.
Increases HR

Question 31

PSNS vs SNS transmitter?

Answer 31

Acetylcholine = PSNS
Adrenaline = SNS