myogenic control of the heart and receptors to pressure and CO2 and pH

Describe the role of Chemoreceptors when there is a rise in CO2 or fall in pH and of the nervous system in the process (4 marks)

• Chemoreceptors in the aorta and carotid artery detect a rise in CO2/or a fall in pH

• This causes them to send impulses to the medulla oblongata

• Which increases the frequency of electrical impulses to the SAN

• Via the sympathetic nervous system

• This causes heart rate to increase, to deliver blood rapidly and remove CO2

Describe the role of Baroreceptors when blood pressure increases and of the nervous system in the process (4 marks)

• Baroreceptors in the aorta and carotid artery detect a rise in blood pressure

• This causes them to send signals to the medulla oblongata

• Which decreases electrical impulses to the SAN

• Via the Parasympathetic nervous system

• This decreases heart rate which lowers the blood pressure

Describe the role of Baroreceptors when blood pressure decreases and of the nervous system in the process (4 marks)

• Baroreceptors in the aorta and carotid artery detect a rise in blood pressure

• This causes them to send signals to the medulla oblongata

• Which increase electrical impulses to the SAN

• Via the Sympathetic nervous system

• This increases heart rate which increases the blood pressure

describe how the heart rate is controlled (6 marks)

The SAN releases electrical impulses/a wave of depolarisation across the atria

Causing them to contract.

The AVN will then release a second wave of depolarisation to the bundle of His in the septum.

The wave of depolarisation travels down the septum to the Purkyne fibres in the walls of the ventricles.

There is a short delay before the Apex and ventricles contract.

Allowing time for the atria to pump all the blood into the ventricles,

The cells depolarise and the cardiac muscle relaxes.

Which part of the brain controls heart rate?

The medulla oblongata

How does the medulla oblongata control heart rate?

Via the autonomic nervous system

Label this diagram

The increasing of heart rate/blood pressure involves the

Sympathetic nervous system

The decreasing of heart rate/blood pressure involves the..

Parasympathetic nervous system

What does the SAN and AVN stand for?

• Sinoatrial node

• Atrioventricular node

Where is the “Bundle of his” located?

In the septum

Where is the “Purkyne fibres located in”?

In the walls of the ventricles

Where is the SAN located in?

In the top of the right atrium

Where is the AVN located in?

Between the right and left ventricle

What does it mean when the cardiac muscle is myogenic?

The cardiac muscle can contract on its own

Without stimulation by nervous impulses

how is the rate of contraction controlled?

By the waves of depolarisation

How does a rise in CO2 in the blood affect blood pH?

It decreases blood pH