6.1.3: Control of heart rate

Question 1

What does myogenic mean?

Answer 1

Heart muscle can initiate its own contraction

Question 2

Where is the sinoatrial node located?

Answer 2

Right atrium (pacemaker)

Question 3

Where is the atrioventricular node located?

Answer 3

border of the right and left ventricle within the right atrium

Question 4

Where is the bundle of His located?

Answer 4

runs through septum

Question 5

Where is the Purkyne fibres located?

Answer 5

Walls of ventricles

Question 6

Process of control of heart rate

Answer 6

• SAN releases wave of depolarisation across atria causing it to contract
• AVN release another wave of depolarisation.
• A nonconductive layer of tissue prevents wave of depolarisation travelling down ventricles
• The bundle of His conducts the wave of depolarisation down the septum and the Purkyne fibres
• The apex and walls of ventricles contract after a delay
• Short delay while AVN transmits second wave of depolarisation so stria can pump blood into the ventricles

Question 7

Role of medulla oblongata in control of heart rate

Answer 7

• Controls on the autonomic nervous system
• Impulses through the sympathetic nervous system: Acceleratory centre linked to SAN releases waves of depolarisation more frequently increasing heart rate
• Impulses through the parasympathetic nervous system: Inhibitory centre linked to SAN releases wave of depolarisation less frequently decreasing heart rate

Question 8

What two factors does heart rate respond in change to?

Answer 8

1) pH
2) Blood pressure

Question 9

What receptors respond to blood pressure?

Answer 9

Baroreceptors

Question 10

What receptors respond to pH?

Answer 10

Chemoreceptors

Question 11

Where are baroreceptors and chemoreceptors found?

Answer 11

Aorta and carotid receptors

Question 12

What happens if CO2 levels increase in blood?

Answer 12

• pH decreases due to CO2 production and lactic acid during high respiratory rates
• Detected by chemoreceptors in walls of aorta and carotid arteries
• More frequent impulses sent to medulla oblongata
• More frequent impulses sent from acceleratory centre in medulla to SA node by sympathetic branch
• More frequent impulses from SA node across atria so heart rate increases

Question 13

What happens if blood pressure increases above normal?

Answer 13

• Detected by baroreceptors in carotid arteries and walls of aorta
• More frequent impulses sent to medulla oblongata
• More frequent impulses sent to inhibitory centre in medulla to SA node in the parasympathetic nerve
• Less waves of depolarisation from SA node across atria so heart rate decreases

Question 14

What happens if blood pressure decreases above normal?

Answer 14

• detected by baroreceptors in walls of aorta and carotid arteries
• More frequent impulses sent to medulla oblongata
• More frequent impulses from acceleratory centre in medulla sent to SAN by sympathetic nerve
• Increases frequency of impulses from SA nodes across atria so heart rate increases