3.6.1.3 Autonomic control of heart rate

Question 1

What functions does the autonomic nervous system control?

Answer 1

heart rate, blood pressure, pupil dilation, digestion

Question 2

Parasympathetic nervous system

Answer 2

• inhibitory effect on body tissues

- neurones release neurotransmitter acetylcholine

Question 3

Sympathetic nervous system

Answer 3

• excitatory effect on body
• neurones release neurotransmitter noradrenaline
• action of noradrenaline means muscles have increased blood supply more more O2 and glucose

Question 4

Increase in impulses in parasympathetic system

Answer 4

• more acetylcholine

- slower heart rate

Question 5

Increase in impulses in sympathetic system

Answer 5

• more noradrenaline

- faster heart rate

Question 6

What are chemoreceptors and where are they found?

Answer 6

• chemical receptors
• in aorta, carotid arteries and medulla
• detect changes in [CO2] & [O2] in blood plasma, and blood pH

Question 7

What are baroreceptors and where are they found?

Answer 7

• pressure receptors
• in aorta and carotid arteries
• detect changes in blood pressure

Question 8

What increases blood pressure?

Answer 8

• increased heart rate

- increase in blood volume (lower water potential in blood e.g. more salt)

Question 9

What decreases blood pressure?

Answer 9

• decreased heart rate

- decreased blood volume

Question 10

Explain how an increase in carbon dioxide changes heart rate

Answer 10

• Increased respiration
• Increases CO2 in blood produces more carbonic acid to lower pH
• chemoreceptors in carotid arteries detect the change and send impulses along the sensory neurones to the medulla
• increase in impulse frequency sent via the sympathetic neurones to the SAN using noradrenaline
• increased impulses from SAN
• more contractions of cardiac muscle - heart rate increases

Question 11

Explain how a decrease in blood CO2 is detected and responded to

Answer 11

• decreased rate of respiration results in less CO2 produces
• less carbonic acid produced in blood - less acidic pH
• chemoreceptors in carotid arteries detect this change and send impulses along the sensory neurones to the medulla
• increase in impulse frequency sent via the parasympathetic neurones to the SAN using acetylcholine
• SAN sends less impulses / inhibitory effect, so cardiac muscle contracts less - reducing heart rate

Question 12

Explain how an increase in blood pressure is detected and responded to

Answer 12

• baroreceptors in aorta and carotid arteries detect increase in blood pressure
• send impulses to medulla
• increased impulses to the SAN via parasympathetic neurones
• release of acetylcholine decreases impulses from SAN