Control of heart rate (copy)- gen

Explain what is meant by myogenic

Cardiac muscle contracts on its own without nervous system/neurone impulses

Describe the location of :

SAN

AVN

Bundle of his

Purkyne fibres

Right atrium

Middle sternum

Run through sturunum at outside

Walls of ventricles inward

Describe how the cardiac cycle is controlled by SAN and AVN

• SAN acts as a pacemaker and initiates the heartbeat

• SAN sends a wave of electrical impulses across the atria causing them to contract

• The non conductive tissue(septum) between atria and ventricles prevent the impulse reaching the ventricles

• There is a short delay at the AVN allowing atria to empty and to fill before they contract

• The AVN sends a wave of electrical activity down the bundle of his and up the Purkyne fibres

• This causes the ventricles to contract from the base upward

What is the advantage of having non conducting tissue

Allows enough time for atria to pump all blood into ventricles

So they are full before they contract

Where are chemoreceptors and pressure receptors involved in controlling heart rate found

Carotid artery

Aortic arch

What is the effect of impulses from the parasympathetic nervous system on heart rate

Which neurotransmitter is involved

Decreases heart rate

The nerve releases acetylcholine to SAN

What is the effect of impulses from the sympathetic nervous system on heart rate

Increases heart rate

Nerve releases noradrenaline into SAN

Describe what happens if there is an increase in CO2 concentration in the blood -exercise

• Decrease in PH detected by chemoreceptors in aortic arch/carotid artery

• More impulses sent to medulla

• Higher frequency of impulses sent down the sympathetic nervous system to SAN

• More noradrenaline released onto SAN

• SAN produces higher frequency of impulses and heart rate increases

Describe what happens if there is a decrease in CO2 concentration in the blood

• Increase in PH detected by chemoreceptors in aortic arch and carotid artery

• Fewer impulses sent to

• Higher frequency of impulses sent down PNS to SAN

• More acetylcholine released onto SAN

• SAN produces lower frequency of impulses and heart rate decreases

Describe what happens if there is an increase in blood pressure

• Increase inBP detected by pressure receptors in wall of aorta and carotid artery

• Higher frequency of impulses sent to the medulla

• Higher frequency of impulses sent down PNS to SAN

• More acetylcholine released onto SAN

• SAN produces a lower frequency of impulses as heart rate decreases

Describe what happens if there is a decrease in blood pressure

• Decrease in Bpm detected by pressure receptors in aortic arch and carotid artery Higher frequency

• Lower frequency of impulses sent to medulla

Higher frequency of impulses sent down SNS to SAN

more noradrenaline released into SAN

SAN produces higher frequency of impulses and heart rate increases

When a wave of electrical activity reaches the AVN there is a short delay before a new wave leaves AVN

Explain the importance

Atria empty and the ventricle fills before the ventricle contracts

Delay contraction of ventricle until after the atria contracts

Describe the route taken when electrical impulses are transmitted from SAN to muscles of ventricles

SAN to cardiac muscle

AVN

To bundle of his /purkyne fibres