Organisms Respond to Changes in their Internal and External Environments: Stimuli, Both Internal and External, are Detected and Lead to a Response - Control of Heart Rate

Question 1

What is the centre responsible for controlling the rate of the heart rate?

Answer 1

• Cardioregulatory centre

Question 2

Where is the cardioregulatory centre located?

Answer 2

• Medulla

- AKA medulla oblongata

Question 3

What are the two discrete parts of the cardioregulatory centre?

Answer 3

• Cardioacceleratory centre

- Cardioinhibitory centre

Question 4

What does the cardioacceleratory centre do?

Answer 4

• Responsible for increasing the heart rate

Question 5

What does the cardioinhibitory centre do?

Answer 5

• Responsible for decreasing the heart rate

Question 6

How are the cardioacceleratory centre and cardioinhibitory centre connected to the SAN? What system are these nerves a part of?

Answer 6

• Centres connected to SAN via nerves

- The nerves form the autonomic nervous system

Question 7

Define the term autonomic nervous system

Answer 7

• A branch of the motor nervous system that carries nerve impulses to muscles and glands
• It controls involuntary activities

Question 8

What are the two groups of the autonomic nervous system?

Answer 8

• Sympathetic nervous system (SNS)

- Parasympathetic nervous system (PNS)

Question 9

What chemical does the SNS secrete?

Answer 9

• Noradrenaline

Question 10

Does the SNS generally speed up or slow down activities?

Answer 10

• Generally speeds up activities

Question 11

What chemical does the PNS secrete?

Answer 11

• Acetylcholine

Question 12

Does the PNS generally speed up or slow down activities?

Answer 12

• Generally slows down activities

Question 13

What factors can change the heart rate?

Answer 13

• Changes in pH

- Changes in blood pressure

Question 14

What receptors detect changes in pH?

Answer 14

• Chemoreceptors

Question 15

Where are chemoreceptors located?

Answer 15

• Carotid arteries

- Medulla

Question 16

How do receptors trigger a change in heart rate?

Answer 16

• Receptors send electrical impulses to medulla along sensory neurones
• Medulla processes information
• Medulla sends impulses to SAN along sympathetic or parasympathetic neurones

Question 17

How does respiration affect blood pH?

Answer 17

• Increased respiration leads to higher CO2 levels
• CO2 dissolves in blood plasma to form carbonic acid, which lowers pH
• Anaerobic respiration produces lactic acid, which lowers pH

Question 18

Does low CO2 levels (high pH) lead to an increase or decrease in heart rate?

Answer 18

• Decrease in heart rate

Question 19

Explain how low CO2 levels (high pH) leads to a change in heart rate

Answer 19

• Chemoreceptors in carotid arteries and medulla detect fall in CO2 levels
• Chemoreceptors send impulses along sensory neurones to medulla (cardioinhibitory centre)
• Medulla increases frequency of impulses sent along parasympathetic sensory neurones to SAN
• These neurones secrete acetylcholine
• Acetylcholine binds to receptors on SAN
• Causes heart rate to decrease -which increases CO2 levels, and lowers pH levels

Question 20

Does high CO2 levels (low pH) lead to an increase or decrease in heart rate?

Answer 20

• Increase in heart rate

Question 21

Explain how high CO2 levels (low pH) leads to a change in heart rate

Answer 21

• Chemoreceptors in the carotid arteries and medulla detect increase in CO2 levels
• Chemoreceptors send impulses to medulla (cardioaccelatory centre)
• Medulla increases frequency of impulses sent along sympathetic sensory neurones to SAN
• These neurones secrete noradrenaline
• Noradrenaline binds to receptors on SAN
• Causes heart rate to increase - which decreases CO2 levels and increases pH levels

Question 22

What receptors detect changes in blood pressure?

Answer 22

• Baroreceptors

Question 23

Where are baroreceptors located?

Answer 23

• Aorta

- Carotid arteries

Question 24

Does high blood pressure lead to an increase or decrease in heart rate?

Answer 24

• Decrease in heart rate

Question 25

Explain how high blood pressure leads to a change in heart rate

Answer 25

• Baroreceptors in the aorta and carotid arteries detect increase in blood pressure
• Baroreceptors send impulses along sensory neurones to medulla (cardioinhibitory centre)
• Medulla increases frequency of impulses sent along parasympathetic neurones to SAN
• These neurones secrete acetylcholine
• Acetylcholine binds to receptors on SAN
• Causes heart to decrease - which decreases blood pressure

Question 26

Does low blood pressure lead to an increase or decrease in heart rate?

Answer 26

• Increase in heart rate

Question 27

Explain how low blood pressure leads to a change in heart rate

Answer 27

• Baroreceptors in the aorta and carotid arteries detect fall in blood pressure
• Baroreceptors send impulses along sensory neurones to medulla (cardioaccelatory centre)
• Medulla increases frequency of impulses sent along sympathetic sensory neurones to SAN
• These neurones secrete noradrenaline
• Noradrenaline binds to SAN
• Causes increase in heart rate - which increases blood pressure