6.1.3 Control of heart rate

Question 1

Define myogenic

Answer 1

Contraction of heart is initiated within the muscle itself rather than by nerve

Question 2

State the name of the 2 nodes involved in heart contraction

Answer 2

Sinoatrial node (SAN)
Atrioventricular node (AVN)

Question 3

Where are the 2 nodes involved in heart contraction located

Answer 3

SAN: within the wall of the right atrium
AVN: near lower end of right atrium in the wall that separates the 2 atria

Question 4

Describe how heartbeats are initiated and coordinated

Answer 4

1. SAN initiates wave of depolarisation
2. The wave of depolarisation spreads across both atria = atrial systole
3. Layer of fibrous, non-conducting tissue delays impulse while ventricles fill and valves close
4. AVN conveys WOD down septum via Bundle of His, which branches into Purkinje fibres along ventricles
5. Causes ventricles to contract from apex upwards

Question 5

State the formula for cardiac output

Answer 5

Cardiac output (CO) = Stroke volume (V) x heart rate (R)

Question 6

What is an autonomic nervous system?

Answer 6

• System that controls involuntary actions of glands and muscles
• 2 subdivisions: sympathetic and parasympathetic

Question 7

State the difference between sympathetic and parasympathetic nervous system

Answer 7

Sympathetic involved in ‘fight or flight’ response: stimulates effectors to speed up activity
Parasympathetic involved in normal resting conditions: inhibits effectors to slow down activity

Question 8

Name the receptors involved in changing heart rate

Answer 8

Baroreceptors (detect changes in blood pressure)
Chemoreceptors (detect changes in pH)

Question 9

State the location of the receptors involved in changing heart rate

Answer 9

Baroreceptors: carotid body
Chemoreceptors: carotid body and aortic body

Question 10

How does the body respond to an increase in blood pressure?

Answer 10

1. Baroreceptors send more impulses to cardioinhibitory centre in the medulla oblongata
2. More impulses to SAN down vagus nerve via parasympathetic nervous system
3. Stimulates release of acetylcholine, which decreases heart rate

Question 11

How does the body respond to a decrease in blood pressure?

Answer 11

1. Baroreceptors send more impulses to cardioacceleratory centre in the medulla oblongata
2. More impulses to SAN via sympathetic nervous system
3. Stimulates release of noradrenaline, which increases heart rate and strength of contraction

Question 12

How does the body respond to an increase in carbon dioxide concentration?

Answer 12

1. Chemoreceptors detect pH decrease and send more impulses to cardioacceleratory centre of medulla oblongata
2. More impulses to SAN via sympathetic nervous system
3. Heart rate increases, so rate of blood flow to lungs increases = rate of gas exchange and ventilation rate increase