- self generating
- 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.
Autonomic Nervous System (ANS)
- 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
Sympathetic System (SS)
- 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
SS and PS are Antogoistic
- Allows activities of internal glands and muscles to be regulated by a balance of the two systems
- e.g. heart rate.
Control of 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 SS
- one that decreases heart rate, linked to sinoatrial node in PS
- centre stimulated depends on pressure and chemical changes in the blood.
- 2 centres
- 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.
Effects of exercise on cardiac output
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
Control by pressure receptors
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 SS to sinoatrial node which increases heart rate.