| Date | May 2010 | Marks available | 6 | Reference code | 10M.3.HL.TZ1.15 |
| Level | Higher level | Paper | Paper 3 | Time zone | Time zone 1 |
| Command term | Explain | Question number | 15 | Adapted from | N/A |
Question
Explain the role of the SA (sinoatrial) node in the cardiac cycle.
Markscheme
SA node is located in the wall of right atrium of heart muscle;
has characteristics of both nerve and muscle tissue;
SA node initiates each impulse;
acts as pacemaker of the heart;
no nerve impulses needed for contraction / myogenic;
connected to nerves which slow/accelerate heart rate;
impulses spread out in all directions through walls of atria;
stimulates atrial systole/contraction;
fibres in walls of atria prevent impulses from reaching ventricles;
impulses reach AV node (after atrial contraction);
Examiners report
There were variable responses from very poor to very good. Many confused the role of the SA node as the pacemaker with the actual opening and closing of the valves in the heart. Candidates did seem to do marginally better on this question 3 than in the other options.
