Controlling heart rate

Question 1

Why is it important hear rate changes?

Answer 1

to ensure the extra oxygen required for increased respiration is delivered

Question 2

How is heart rate formed?

Answer 2

• involuntarty and controlled by the autonomic nervous system
• the medulla oblongata in the brain is responsible for controlling heart rate and making any necessary changes

Question 3

What are the two centres within the medulla oblongate do?

Answer 3

both are linked to the sinoatrial node in the heart by motor neurones

• one centre increases heart rate by sending impulses through the sympathetic nervous system, these impulses are transmitted by the accelerator nerve
• once centre decreases heart rate by sending impulses through the parasympathetic nervous system, these impulses are transmitted by the vagus nerve

Question 4

Which centre is stimulated depnds on what?

Answer 4

the information received by receptors in the blood vessels

Question 5

What are the two types of receptors?

Answer 5

• baroreceptors (pressure receptors)
  
  • these receptors detect changes in blood pressure
  • for example, if a person’s blood pressure is low, the heart rate needs to increase to prevent fainting
  • barorecptors are present in the aorta, vena cava, and cartoid arteries
• chemoreceptors (chemical receptors)
  
  • these recptors detect change sin the level of particular channels in the blood such as carbon dioxide
  • located in the aorta, the cartoid artery (mahor arter in neck that supplies the brain with blood), and the medulla

Question 6

Describe the steps involved with the effects of exercise on cadiac output?

Answer 6

• increased muscular/metabolic acitivity
• more carbon dioxide produced by tissues from increased respiration
• blood pH is lowered
• centre in medulla oblongata that speeds heart rate, increases the freq. of impulses to SAN via the sympathetic nervous system
• SAN increases heart rate
• carbon dioxide levels return nomral

Question 7

What happens as CO2 levels decrease?

Answer 7

• pH rises
• detected by chemoreceptors in the wall of the cartoid arteries and the aorta
• results in a reduction in the frequency of nerve impulses being sent to the medulla oblongata
• reduced freq of impulses beign sent to the SAN via the sympathetic nervous system, and thus heart rate decreases back to it normal level

Question 8

How is blood pressure returned to normal levels?

Answer 8

• barorecpotrs present in the aorta and cartoid artery wall detect changes in pressure
• if pressure is too low/high, impulses are sent to the medulla blongata centre which decreases/increases heart rate
• send impulses along the parasympathetic/vagus neurones to the SAN which decreases/increases teh rate at which the heart beats

Question 9

How is heart rate controlled by hormones?

Answer 9

• in times of stress adrenaline and noradreanline
• affect the pacemaker of the heart itself
• speed up the heart rate by increaseing the freq of impulses produced by the SAN

Question 10

Stimulus - high blood pressure

receptor - ?

neurone - ?

effector - ?

response - ?

how is this different for chemicals

Answer 10

• receptor
  
  • barorecptors
• neurone
  
  • impulse sent to the medulla,
  • which sends impulses along the vagus nerve
  • this secretes acetycholine, which binds to receptors on SAN
• effector
  
  • cardiac muscles
• response
  
  • heart rate slows down
• stimulus is high blood O2 low CO2 or high pH
• chemoreceptrrs
• same neurone and response

Question 11

Stimulus - low blood pressure

receptor - ?

neurone - ?

effector - ?

response - ?

How is this different for chemicals?

Answer 11

• receptro
  
  • barorecptors
• neurone
  
  • impulse sent to medulla
  • send impulses along the accelerator nerve
  • this secretes noradrenaline
  • which binds to receptros on SAN
• effector
  
  • cardiac muscle
• response
  
  • heart rate speeds up
  • increase blood pressure to normal
• low blood O2
• chemoreceptors
• same neurone, effector and response