5.5.12 Factors Affecting Heart Rate

Question 1

What does myogenic mean?

Answer 1

• No external stimuli needed to initiate contraction
• Cardiac muscle in heart as an example

Question 2

What is the autonomic nervous system?

Answer 2

• Medulla split into 2 parts
• Acceleratory centre (causes heartrate to speed up)
• Inhibitory centre (causes heartrate to slow down)
• Connected to sinoatrial node by nerves
• Self controlling

Question 3

How does the acceleratory centre work?

Answer 3

• Acceleratory centre activated
• Impulses sent to SAN along sympathetic neurones
• Noradrenaline secreted at synapse within SAN
• Causes SAN to increase frequency of electrical waves it produces to initiate heartbeat
• Increased heartrate

Question 4

How does the inhibitory centre work?

Answer 4

• Activated
• Impulses sent along parasympathetic neurones to SAN
• Acetylcholine secreted at synapse with SAN
• Reduces frequency of electrical waves it produces initiating heartbeat
• Reduces elevated heartrate to resting rate

Question 5

How are the acceleratory and inhibitory centres triggered for activation?

Answer 5

• CO2 concentration increase of blood
• Fall in blood pressure from dilating muscle arterioles
• Chemoreceptors and pressure receptors in aorta
• When change is detected, nerve impulses released and sent to acceleratory and inhibitory centers which are the coordinators
• Low frequency impulses activate inhibitory centre to slow heartrate
• High frequency impulses activate acceleratory centre to speed up heartrate

Question 5

What hormones increase heartrate?

Answer 5

• Adrenaline and noradrenaline
• Thyroxine