6.3 Control of heart rate

Question 1

What does myogenic mean?

Answer 1

Can contract and relax without receiving electrical impulses from nerves

Question 2

How is the heart able to contract?

Answer 2

• SAN acts as a pacemaker, releasing electrical impulse across atria
• Causing atria to contract simultaneously
• Non-conducting tissue between atria and ventricles prevents impulse passing directly to ventricles
• Waves of electrical activity reach AVN which delays impulse
• Allowing atria to fully contract and empty before ventricles contract
• AVN sends electrical impulse down bundle of His to Purkyne tissue
• Causing ventricles to contract simultaneously base up

Question 3

Where are baroreceptors and chemoreceptors located?

Answer 3

Aorta and carotid arteries

Question 4

Increasing heart rate

Answer 4

• Baroreceptors detect fall in blood pressure / chemoreceptors detect fall in blood pH
• Send impulses to medulla
• Which sends more frequent impulses to SAN along sympathetic neurones
• So more frequent impulses sent from SAN to AVN
• So cardiac muscle contracts more
• So heart rate increases

Question 5

Decreasing heart rate

Answer 5

• Baroreceptors detect rise in blood pressure / chemoreceptors detect rise in blood pH
• Send impulses to medulla
• Which sends more frequent impulses to SAN along parasympathetic neurones
• So less frequent impulses sent from SAN to AVN
• So cardiac muscle contracts less
• So heart rate decreases