Control Of Heart Rate

Question 1

Cardiac muscle is ____________

Answer 1

Cardiac muscle is ____________

Question 2

Define myogenic

Answer 2

Contraction is initiated from within the muscle itself;

due to the action of the sinoatrial node (SAN)

(which acts as a ‘pacemaker’)

Question 3

Nodes required for initiation and coordination of a heartbeat / cardiac cycle.

Answer 3

Sinoatrial node (SAN)

Atrioventricular node (AVN)

Note: you only need to recall ‘SAN’ and ‘AVN’

Question 4

SAN location

Answer 4

Upper wall of right atrium

Question 5

AVN location

Answer 5

Base of right atrium

Question 6

bundle of his location

Answer 6

(ventricular) septum

Question 7

The sinoatrial node (SAN) is in the right atrium of the heart. Describe the role of the sinoatrial node (2 marks).

Answer 7

Sends out waves of electrical activity / impulses;

Which stimulates the contraction of atria OR acts as a ‘pacemaker’;

Question 8

Describe how a heartbeat is initiated and coordinated (5 marks).

Answer 8

1. SAN sends wave of electrical activity / impulses across atria causing atrial contraction;
2. Non-conducting tissue prevents impluse spreading to the ventricles
3. AVN delays impulse whilst blood leaves atria and the ventricles fill;
4. AVN sends wave of electrical activity / impulses down the Purkinje fibres / bundle of His;
5. Causing ventricles to contract from base up;

Question 9

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 marks).

Answer 9

1 Electrical activity only through AVN / purkinje fibres / bundle of His;

2. Wave of electrical activity passes over / through both ventricles at the same time;

Question 10

Cardiac output equation

Answer 10

Cardiac output (CO) = stroke volume (SV) x heart rate (HR)

NOTE: Cardiac output is one spec for paper 2 AND paper 1

Question 11

TRUE or FALSE:

Heart rate is the length of one cardiac cycle in seconds

Answer 11

FALSE

Heart rate is the number of cardiac cycles / heart beats per minute

Question 12

One cardiac cycle is 0.85s, what is the heart rate?

Answer 12

60 / 0.85 = 70.588 or 71 bpm

Question 13

Heart rate of 62 bpm and a cardiac output of 4785cm^3 min^-1 - what is the stroke volume?

Answer 13

77 cm^3

Question 14

Convert 620 milliseconds (ms) into seconds (s)

Answer 14

620 / 1000 = 0.62s

Question 15

Convert 4.27 seconds (s) into milliseconds (ms)

Answer 15

Convert 4.27 seconds (s) into milliseconds (ms)

Question 16

Branches of the autonomic nervous system

Answer 16

Branches of the autonomic nervous system

Question 17

increased activity of the ____________ nervous system increases heart rate

Answer 17

sympathetic

Question 18

Increased activity of the ____________ nervous system decreases heart rate

Answer 18

parasympathetic

Question 19

Receptors for blood pressure

Answer 19

baroreceptors

Question 20

Baroreceptor location

Answer 20

aorta

carotid artey*

*supply blood to brain

Question 21

Cardiac centres location

Answer 21

Medulla oblongata

Question 22

Neurotransmitter released by parasympathetic nervous system

Answer 22

acetylcholine

Question 23

Explain how a rise in blood pressure results in a decrease in heart rate (6 marks).

Answer 23

1. Baroreceptors in the aorta / carotid arteries
2. Send impulses to cardiac centres / medulla oblongata;
3. Increased frequency of impulses sent via parasympathetic nerves;
4. to SAN;
5. Release of acetylcholine inhibits SAN so decreases impulses;
6. So decreased implules to AVN;

Question 24

Neurotransmitter released by sympathetic nervous system

Answer 24

noradrenaline

Question 25

suggest how caffeine increases heart rate (2 marks)

Answer 25

1. More impulses/action potentials along sympathetic nervous system; 2. To SAN

Question 26

Receptors for carbon dioxide concentration in blood

Answer 26

aorta carotid artey* *supply blood to brain --

Question 27

Control of heart rate (AO1) Exercise causes an increase in heart rate. Describe the role of receptors and of the nervous system in this process (4 marks).

Answer 27

1. Chemoreceptors detect rise in carbon dioxide in blood 2. Send impulses to cardiac centres / medulla oblongata; 3. More / increases frequency of impulses to SAN; 4. via sympathetic nervous system;

Question 28

Some drugs inhibit the transmission of nerve impulses to the heart. Explain how these drugs reduce blood pressure (2 marks).

Answer 28

1. Inhibit impulses along sympathetic nervous system; 2. SAN not stimulated so less waves of electrical activity / impulses spread across atria;