Control of heart rate

• Autonomic
  • self generating
• Antogolistic
• • if one system contracts a muscle then the other will relax it
• Medulla Oblongata
  • centre of the brain that controls heart rate
• Carotid arteries
  • arteries that serve the brain
• Pressure receptors
  • occur within walls of carotid arteries and the aorta.

2 parts:

• Sympathetic nervous system
• Parasympathetic nervous system

Both haves nerves that emerge from the brain and go to organs concerned.

ANS = involutarily controls activities of internal muscles and glands

• stimulates effectors
• speeds up activity
• emergency controller
  • used during strenous excersis and when experiencing powerful emotions
• makes us more aware of surroundings.

• inhibits effectors
• slows down activity
• controls activities under normal resting conditions
• conserves energy and replenishes supplys

• Allows activities of internal glands and muscles to be regulated by a balance of the two systems
  • e.g. heart rate.

• Resting rate of an adult varies depending on demands for oxygen
  • e.g. excessive increases demand
• Medulla oblongata
  • 2 centres
    • one that increases heart rate which is linked to sinoatrial node in **
    • one that decreases heart rate, linked to sinoatrial node in PS
  • centre stimulated depends on pressure and chemical changes in the blood.

• found in wall of Carotid arteries
• sensitive to changes in pH of blood
  • changes due to carbon dioxide conc.
• Process of control:
  • higher than normal conc of carbon dioxide
  • chemoreceptors detect this and increase freq of nervous impulses to medulla oblongata
    • increases heart rate
  • centre increases freq of impulses via SNS to sinoatrial node which increases heart rate.
  • increases blood flow means more CO2 removed and pH returned to normal
  • medulla oblongata reduces freq of impulses and decreases heart rate to normal.

Increased muscular/metabolic activity

--> more CO2 produced as increased respiration

--> blood pH is lowered

--> chemical receptors in the carotid arteries increase frequency of impulses to medulla oblongata

--> SA node increases heart rate

--> increases blood flow removes CO2 faster

--> CO2 level returns to normal

Operate as follows:

• When blood pressure higher than normal
  • nervous impulse is transmitted to medulla oblongata to decrease heart rate
  • impulses go via PS to sinoatrial node
• When blood pressure is lower than normal
  • transmit a nervous impulse to medulla oblongata that increases heart rate
  • sends impulses via ** to sinoatrial node which increases heart rate.