electrical properties of the heart

Question 1

Describe what a tetanic contraction is

Answer 1

• Only in skeletal muscle
• Due to the short refractory periof, there is consecutive twitch contractions which can summate

Question 2

Describe why the heart has no tetanic contraction

Answer 2

The action potential is very long, the refractory period is therefore very long which means that tetanic contractions is not possible

Question 3

What does the NA/K atpase pump do

Answer 3

Pumps 2 potassium into the cell and 3 sodium out of the cell which mantains the resting potential of -90 mV

Question 4

Describe the non pacemaker action potential

Answer 4

1. Leaky potassium channel open
2. Rapid depolarisation due to sodium channels opening
3. sodium channels close and calcium channels open
4. calcium channels close

Question 5

What causes the pace maker cells to reach action potential

Answer 5

Calcium channels opening which causes depolarisation

Question 6

What is the function of the atrioventricular node

Answer 6

Acts as a delay box and allows time for the atria to depolarise and contract and squeeze blood into the ventricles before the ventricles contract

Question 7

Describe the usual ECG

Answer 7

P wave - atrial depolarisation
QRS - ventricular depolarisation
T wave - ventricular repolarisation

Question 8

Why is there no atrial repolarisation seen on ECG

Answer 8

Because it happens at the same time as the ventricular depolarisation so gets lost in the QRS wave

Question 9

What node is the pace maker

Answer 9

Sinoatrial node

Question 10

Describe the bundle of His and Purkinje fibres

Answer 10

Rapid conducting system