Control of Heart Rate

Question 1

What is myogenic?

Answer 1

Muscle can initiate its own contractions. This can happen due to SAN (pacemaker)

Question 2

What supplies the nervous impulse?

Answer 2

The nerves from the medulla oblongata

Question 3

Where is the medulla oblongata found?

Answer 3

• Base of brain

- The region that co-ordinates the unconscious functions of the body

Question 4

If adrenaline increases, how does heart muscle respond?

Answer 4

• Beats faster and stronger

Question 5

What are the 2 main nodes found in the heart?

Answer 5

• Sinoatrial node (SAN)

- Atrioventricular node (AVN)

Question 6

How is heart rate controlled?

Answer 6

1) SAN sends an electrical impulse over atrial walls
2) This causes atria to contract
3) Conducted to AVN, where the electrical wave of excitation is conducted down Purkinje fibres
4) Causes ventricular to contract
5) Layer of insulation between atria and ventricles prevents first wave from travelling all the way down
6) This layer cause a delay at the AVN

Question 7

What does the medulla oblongata do?

Answer 7

• Ivolved in unconcious functions e.g. breathing
• Can sense factors that require change in heart rate
• Cardiovascular centre can detect CO2 levels

Question 8

How does movement affect heart rate?

Answer 8

• Limb movement is detected by stretch receptors
• Impulse to CV centre, signals that oxygen is needed
• Heart rate increases

Question 9

How does exercise affect heart rate?

Answer 9

• Muscles release more CO2
• CO2 lowers pH of blood which is detected by chemoreceptors that send impulses to CV centre
• Chemoreceptors fire action potentials that are passed to CV centre of medulla obongata
• Impulse sent to accelerator nerve increases heart rate

Question 10

How does adrenaline affect heart rate?

Answer 10

• Secreted as a response to stress
• Presence increases heart rate
• Adrenaline binds to specific receptors on cell membranes in SAN

Question 11

How does blood pressure affect heart rate?

Answer 11

• Monitored by pressure receptors in wall of carotid sinus
• Too high- CV centre is signalled
• Signals sent through vagus nerve to decrease heart rate

Question 12

What is the sympathetic nervous system?

Answer 12

Stimulates effectors to speed up activity.

Question 13

What is the parasympathetic nervous system?

Answer 13

Inhibits effectors to slow down activity

Question 14

Explain how both ventricles contracting at the same time is coordinated in the heart after initiation of the heartbeat by the SAN?

Answer 14

The impulse travels down the bundle of His and passes across both ventricles at the same time