Wednesday 28 November 2012

exam question & markscheme on control of the cardiac cycle

 
(a)
The cardiac cycle is controlled by the sinoatrial node (SAN) and the atrioventricular node (AVN). Describe how.
(5)

markscheme:

(a) 
1.SAN initiates heartbeat / acts as a pacemaker / myogenic;
Q Must be in context
2.(SAN) sends wave of electrical activity / impulses (across atria)
causing
atrial contraction;
Reject: signals / electronic / messages / nerve impulses once only
3.AVN delays (electrical activity / impulses);
Neutral: reference to non-conducting tissue delaying impulses instead of the AVN
4.(Allowing) atria to empty before ventricles contract / ventricles
to fill before they contract;
5.(AVN) sends wave of electrical activity / impulses down
Bundle of His / Purkinje fibres;
6.(Causing) ventricles to contract (from base up) / ventricular
systole;  5 max

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