'A' Level Medical Option Questions - The Heart - ECG


(a) Describe the response of the heart to the action potential originating at the sino-atrial node.

  • The pulse causes atria muscles to contract
  • Blood is forced into the ventricles
  • The pulse is delayed before firing ventricular node
  • ventricles contract
  • this forces blood out of heart to lungs and body

4 marks

(b) The cell membrane action potential changes with time as shown. The change in action potential results from ion movement in the same way as does the change of action potential across a nerve membrane. AB is a region of depolarisation. CD is a region of repolarisation.

(i) Describe the ion movement which produces depolarisation.

Na+ move from from outside to inside

(ii) Describe the ion movement which produces repolarisation.

K+ from inside to outside

3 marks

Total 7 marks