14.6 Controlling Heart Rate

Question 1

Which part of the brain is most reponsible for controlling heart rate?

Answer 1

medulla oblongata

Question 2

Which centre in the medulla is linked to the sympathetic nervous system & accelerator nerve?

Answer 2

centre for increasing heart rate

Question 3

Which centre in the medulla is linked to the parasympathetic nervous system & vagus nerve?

Answer 3

centre for decreasing heart rate

Question 4

To increase the heart rate, the medulla sends [increased/decreased] frequency of electrical impulses to the ____ via the ____ nerve of the _____ nervous system.

Answer 4

increased

SAN

accelerator

sympathetic

Question 5

To decrease the heart rate, the medulla sends [increased/decreased] frequency of electrical impulses to the ____ via the ____ nerve of the _____ nervous system.

Answer 5

decreased

SAN

vagus

parasympathetic

Question 6

The centre in the medulla for increasing the heart rate is linked to the SAn by the ____ nerve of the ____ nervous system.

Answer 6

accelerator

sympathetic

Question 7

The centre in the medulla for decreasing heart rate is linked to the SAN by the ____ nerve of the ____ nervous system.

Answer 7

vagus

parasympathetic

Question 8

What are the type of receptors detecting changes in blood pH?

Answer 8

chemoreceptors

Question 9

What stimuli do chemoreceptors detect?

Answer 9

changes in blood pH

Question 10

What are the type of receptors which detect changes in blood pressure?

Answer 10

baroreceptors

Question 11

What stimuli do baroreceptors detect?

Answer 11

changes in blood pressure

Question 12

Where are baroreceptors for detecting changes in blood pressure located?

Answer 12

aorta, carotid artery

Question 13

Where are chemoreceptors for detecting changes in blood pH located?

Answer 13

aorta, carotid artery, medulla

Question 14

Explain what happens to increase the heart rate when CO₂ concentration in the blood is too high:

Answer 14

increased CO₂ forms more carbonic acid, H₂CO₃

(CO₂ + H₂O ⟶ H₂CO₃)

carbonic acid dissociates, decreasing blood pH

decrease in pH detected by chemoreceptors in aorta/carotid artery/medulla

increased frequency of impulses from chemoreceptors ⟶ to centre in medulla for increasing heart rate

increased frequency of impulses from medulla ⟶ SAN

SAN increases heart rate

faster blood flow through lungs

CO₂ removed faster, restoring normal blood pH

Question 15

Explain what happens to decrease the heart rate when CO₂ concentration in the blood is too low:

Answer 15

• decreased CO₂ forms less carbonic acid, H₂CO₃
  
  • (CO₂ + H₂O ⟶ H₂CO₃)
• lower concentration of H⁺, so pH increases
• increase in pH detected by chemoreceptors in aorta/carotid artery/medulla
• increased frequency of impulses from chemoreceptors ⟶ to centre in medulla for decreasing heart rate
• decreased frequency of impulses from medulla ⟶ SAN
• SAN decreases heart rate
• slower blood flow through lungs
• CO₂ & H₂CO₃ concentration increases, restoring normal blood pH

Question 16

If the blood pH increases above normal range, the heart rate must…

Answer 16

decrease

(decreases blood flow through lungs, increases CO₂ + H₂CO₃ concentration, decreases pH back to normal)

Question 17

If the blood pH decreases below normal range, the heart rate must…

Answer 17

increase

(increases blood flow through lungs, decreases CO₂ + H₂CO₃ concentration, increases pH back to normal)

Question 18

What receptor & nervous system is involved when the blood pH increases above normal range?

Answer 18

chemoreceptors

parasympathetic (to decrease heart rate, increase CO₂ + H₂CO₃ concentration)

Question 19

What receptor & nervous system is involved when the blood pH decreases below normal range?

Answer 19

chemoreceptors

sympathetic (to increase heart rate, decrease CO₂ + H₂CO₃ concentration)

Question 20

Explain what happens to decrease the heart rate when the blood pressure is too high:

Answer 20

• Detected by baroreceptors in aorta/carotid artery
• Increased frequency of impulses ⟶ medulla
  
  • centre for decreasing heart rate
• Decreased frequency of impulses ⟶ SAN
  
  • (through parasympathetic nervous system, vagus nerve ∵ ￬ heart rate)
• SAN decreases heart rate
• So blood pressure decreases to normal

Question 21

Explain what happens to increase the heart rate when the blood pressure is too low:

Answer 21

• Detected by baroreceptors in aorta/carotid artery
• Increased frequency of impulses ⟶ medulla
  
  • centre for increasing heart rate
• Decreased frequency of impulses ⟶ SAN
  
  • (through parasympathetic nervous system, vagus nerve ∵ ￬ heart rate)
• SAN decreases heart rate
• So blood pressure decreases to normal

Question 22

Why does increased metabolic activity result in low blood pH?

Answer 22

increased demand for energy/ATP

increased rate of respiration

produces more CO₂, increasing concentration in blood

CO₂ + H₂O ⟶ H₂CO₃

dissociates, increasing H⁺ concentration

decreases blood pH

Question 23

Why may an athlete’s heart rate increase just before a race has begun?

Answer 23

stress

causes release of adrenaline/noradrenaline

increases the frequency of impulses from medulla to SAN

increasing heart rate

Question 24

How can the heart rate be influenced by hormones?

Answer 24

adrenaline/noradrenaline increase frequency of impulses sent to SAN

increasing heart rate