Conduction

Question 1

Label the diagram

Answer 1

Question 2

Describe what happens at each phase of an action potential

Answer 2

0. Rapid influx of Na+
1. Voltage gated Na+ channels close & voltage gated K+ channels open
2. Ca2+ influx, K+ efflux
3. Ca2+ channels close
4. K+ channels close

Question 3

Describe the sympathetic & parasympathetic effect on SA node

Answer 3

Sympathetic effect SA node:
Adrenaline activates B-adrenergic receptors on cell membranes of pacemaker cells
Increases heart rate as pacemaker cells reach threshold quicker

Parasympathetic effect SA node:
Acetylcholine activates muscarinic cholinergic receptors on cell membranes of pacemaker cells
Slows ion channel changes
Decreases heart rate as pacemaker cells reach threshold slower

Question 4

Describe the sympathetic & parasympathetic effect on AV node

Answer 4

Sympathetic effect AV node:
Increases velocity of action potential & shortens refractory period
Increases heart rate

Parasympathetic effect AV node:
Decreases velocity of action potential & increases refractory period

Decreases heart rate

Question 5

Describe sympathetic effect on cardiac myocytes

Answer 5

Cardiac myocytes have B-adrenergic receptors that are activated by adrenaline

Adrenaline causes bigger action potentials which leads to stronger & quicker contractions

This is because more Ca2+ channels open –> increase in Ca2+ entering cell –> increased membrane potential

K+ channels also open sooner which speeds up repolarisation

Parasympathetic doesn’t have effect as few ventricular muscle cells receive direct parasympathetic input

Question 6

Label the diagram

Answer 6

Question 7

Fill in the table

Answer 7