Outline normal impulse generation and conduction in the heart. Describe the features present in a normal heart that prevent generation and conduction of arrhythmias.
This question required description of the SA node, its primary role and generation of the
pacemaker potential and the influence of the autonomic nervous system. A diagram of the
conducting pathways, highlighting specialized tissues with fast or slow conduction velocities
would have been appropriate. The importance of the AV node in preventing retrograde
conduction and high rates conducted to the ventricles (>220 / min) was often neglected in
answers. A discussion of the Purkinje Fibres with particular reference to the absolute and
relative refractory periods was essential.
Additional marks were awarded for mention of the atrial internodal pathways, conduction
within the ventricles from the endocardial to epicardial surfaces and the significance of the
compensatory pause in response to ectopic beats.
Syllabus C1b 2.a, b;
Reference: Cardiovascular Physiology, “Electrical Activity of the Heart” (Chapter 2), Berne
This question expected a lot, judging from the examiner's comments. How to roll this answer into a compact form, readily expelled over ten minutes of frantic scribbling? Here, an attempt is made to concentrate all the relevant features mentioned in the college answer, with the greatest economy of words.
Normal conduction in the heart (in order of conduction)
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