Heart Activity (pages 84 - 85)

Question 1

Cardiac (heart) muscle is ‘myogenic’. What does this mean?

Answer 1

It can contract and relax without receiving signals from nerves.

Question 2

Where do the Myogenic process start?

Answer 2

in the sino-atrial node (SAN), which is in the wall of the right atrium.

Question 3

What is SAN (sino-artrial node) similar to?

Answer 3

it is similar to a pacemaker - it sets the thythem of the heartbeat by sending out regular waves of electrical activity to the atrial walls.

This causes the right and left atria to contract at the same time.

Question 4

A band of non-conducting collagen tissue prevents the waves of electrical activity from being passed directly from what to what?

Answer 4

from the ATRIA to the VENTRICLES

Instead, these waves of electrical activity are transferred from the SAN to the atrioventricular node (AVN)

Question 5

What is the AVN (atrioventricular node) responsible for?

Answer 5

for passing the waves of electrical activity on to the bundle of His. But, there’s a slight delay before the AVN reacts, to make sure the ventricles contract after the atria have emptied.

Question 6

What is the ‘bundle of His’?

Answer 6

is a group of muscle fibres responsible for conducting the waves of electrical activity to the finder muscle fibres in the right and left ventricle walls, called the Purkyne tissue’

Question 7

what is the function of the ‘Purkyne tissue?

Answer 7

carries the waves of electrical activity into the muscular walls of the right and left ventriciles, causing them to contract simultaneously, from the bottom up.

see diagram 1 on page 84 of the heart.

Question 8

A doctor can check someone’s heart function using what machine?

Answer 8

electrocardiograph. - a machine that records the electrical activity of the heart.

The heart muscle depolarises (loses electrical charge) when it contracts, and repolarises (regains charge) when it relaxes.

Question 9

Why are electrodes placed on the chest of someone having an electrocardiograph reading?

Answer 9

an electrocardiograph records the changes in electrical charge using electrodes placed on the chest.

The trace produced by the electrocardiograph is called an electrocardiogram or ECG. a normal ECG looks like the digaram 2 on page 84.

Question 10

Look at diagram 2 on page 84, of a normal ECG (electrocardiogram), What is the P wave caused by?

Answer 10

the P wave is caused by contraction (depolarisation) of the atria.

Question 11

Look at diagram 2 on page 84, of the normal ECG, the main peak of the heartbeat, together with the dips at either side is called QRS complex, what do this mean?

Answer 11

QRS complex - its caused by contraction (depolarisation) of the ventricles.

Question 12

Looking at diagram 2 on page 84 of a normal ECG, what is the T wave due to?

Answer 12

the T wave is due to relaxation (repolarisation) of the ventricles.

Question 13

Look at diagram 2 on page 84, of a normal ECG, what do the height wave indicate?

Answer 13

this indicates how much electrical charge is passing through the heart - a bigger wave means more electrical charge, so (for the P and R waves) a bigger wave means a stronger contraction

Question 14

name the cardiac muscle (myogenic) contractions that controls the regular heartbeat (six in total)

Answer 14

Sino-atrial node (SAN)
waves of electrical activity
AVN (atrioventricular node
Purkyne tissue
bundle of His
Non-conducting collagen tissue.

Question 15

Why do Doctors use ECG’s (electrocardiogram) for?

Answer 15

for heart problems. Doctors compare their patients’ ECGs with a normal trace. This helps them to diagnose any heart problems.

Question 16

What is Tachycardia? look at diagram 1 on page 85 of ECG

Answer 16

this is where the heartbeat is too fast. around 120 beats per minute. (this is called tachycardia.

this might be OK during excercise, but at rest it shows that the heart isn’t pumping blood efficiently.

Question 17

What is Bradycardia?

Answer 17

A heartbeat that is too slow - below 60 beats per minute at rest.

Question 18

Look at diagram 2 on page 85, the 5th heartbeat on this ECG is an ectopic heartbeat, what do this mean?

Answer 18

Ectopic heartbeat is an extra heartbeat. this diagram shows its caused by an earlier contraction of the atria than in the previous heartbeats (you can see the P wave is different and that it comes earlier than it should). However, it can be caused by early contraction of the bentricles too. Occational ectopic heartbeats in a healthy person don’t cause a problem.

Question 19

Look at ECG diagram on page 85 diagram 3. this is called Fibrillation, what is this?

Answer 19

fibrillation a really irregular heartbeat. The atria or ventricles completely lose their rhythm and stop contracting properly. It can result in anything from chest pain and fainting to lack of pulse and death.

Question 20

What prevents impulses from the atria travelling straight into the ventricles?

Answer 20

A band of non-conducting collagen tissue prevents the waves of electrical activity from being passed directly from the atria to the ventricles.

Question 21

What is the name of the structure that picks up impulses from the atria and passes them on to the ventricles?

Answer 21

The AVN (atrioventriciclar node) is responsible for passing the waves of electrical activity on to the bundle of His. But, there’s a slight delay before the AVN reacts, to make sure the ventricles contract after the atria have emptied.

the bundle is His is a group of muscle fibres responsible for conducting the waves of electrical activity to the finer muscle fibres in the right and left ventricle walls, called the purkyne tissue.

Question 22

What causes the QRS part of an ECG trace?

Answer 22

the main peak of the heartbeat together with the dips at either side is called the QRS complex, its caused by contraction (depolarisation) of the ventricles.

Question 23

Describe the function of:

a) the sino-atrial node (1 mark)
b) the Purkyne tissue (1 mark)

Answer 23

a) The sino-atrial node acts as a pacemaker/initiates heartbeats (1mark)
b) the Purkyne tissue conducts electrical impulses through the ventricle walls (1mark)

Question 24

Sugges the cause of an ECG which has a QRS complex that is not as high as normal (2 marks)

Answer 24

The ventricles are not contracting properly (1 mark). This could be because of muscle damage/because the AVN is not conducting impulses to the ventricles properly (1 mark)