Electrical Activity of the Heart

Question 1

Why is the SAN the natural pacemaker of the heart?

Answer 1

It is the fastest firing node in the heart, therefore drives the heart rate. Purkinje fibres rarely set heart rate because they are the slowest firing cells.

Question 2

Describe how the sympathetic nervous system acts on receptors to increase heart rate.

Answer 2

Sympathetic neurones release noradrenaline to act on B1-adrenoceptors in SAN

Question 3

Describe how the parasympathetic nervous system acts on receptors to decrease heart rate.

Answer 3

Parasympathetic neurones release acetylcholine to act on M2-muscarinic receptors in the SAN