Control of Heart Rate

Question 1

What is the heart muscle called?

Answer 1

• Cardiac muscle

Question 2

What is meant by myogenic?

Answer 2

The contraction is initiated from within the muscle itself rather than from electrical impulses.

Question 3

What is the sinoatrial node?

Answer 3

A distinct group of cells in the right atrium that determines the beat of the heart. (pacemaker)

Question 4

Where is the atrioventricular node?

Answer 4

Lies between the atria.

Question 5

What do the purknye fibres make up?

Answer 5

The Bundle of His

Question 6

Explain how the bicuspid valve maintains a unidirectional flow of blood. (2)

Answer 6

1) When pressure in left atrium is higher than pressure in the left ventricle causing valve to open.
2) When pressure in the left ventricle is higher than pressure in the left atrium, the valve closes.

Question 7

When the heart beats, both ventricles contract at the same time.
Explain how this is coordinated in the heart after initiation of the heartbeat
by the SAN. (2)

Answer 7

1) Electircal activity only through Bundle of His.
2) Wave of electrical activity passes through both ventricles at the
same time.

Question 8

Describe how a heartbeat is initiated and coordinate. (5)

Answer 8

1) SAN sends wave of electrical activity causing atrial contraction.
2) Non-conducting tissue prevents immediate contraction of ventricles.
3) AVN delays impulse whilst blood leaves atria.
4) AVN sends wave of electrical activity down Bundle of His.
5) Causing ventricles to contract from base up.

Question 9

Explain how the heart muscle and the heart valves maintain a one-way flow of blood from the left atrium to the aorta. (5)

Answer 9

1) Atrium has higher pressure than ventricles causing AV valves to open.
2) Ventricle has higher pressure than atrium causing AV valve to close.
3) Ventricle has higher pressure than aorta causing semilunar valve to open.
4) Higher pressure in aorta than ventricle causing semilunar valve to close.
5) Muscle contraction causes an increase in pressure.

Question 10

The heart controls and coordinates the regular contraction of the atria and ventricles. Describe how. (5)

Answer 10

1) SAN -> AVN -> Bundle of His.
2) Electrical activity over atria.
3) Atria contract.
4) Non-conducting tissue
5) Delay at AVN ensures atria empty.
6) Ventricles contract from apex upwards.

Question 11

When a wave of electrical activity reaches the AVN, there is a short delay before a new wave leaves the AVN. Explain the importance of this short delay. (2)

Answer 11

1) Allows atria to empty
2) Before ventricles contract.

Question 12

The sinoatrial node (SAN) is in the right atrium of the heart. Describe the role of the sinoatrial node.

Answer 12

1) Sends out electrical impulses.
2) Acts as a pacemaker.

Question 13

Describe the route taken when electrical impulses are transmitted from the sinoatrial node to muscles of the ventricles in a healthy heart. (2)

Answer 13

1) Through cardiac muscle.
2) To atrioventricular node.