Control Of The Heart Rate

Question 1

What is the somatic nervous system?

Answer 1

It controls conscious actions.

Question 2

What is the automatic nervous system?

Answer 2

It control unconscious actions.

Question 3

What is the sympathetic part of the automatic nervous system?

Answer 3

It speeds the body up and gets it ready for action.

Question 4

What is the parasympathetic part of the automatic nervous system?

Answer 4

It slows the body down.

Question 5

What are chemoreceptors and where are they found?

Answer 5

1. They are receptors that detect a change in oxygen and carbon dioxide in the blood.
2. They are found in the medulla, aorta and carotid arteries.

Question 6

What are baroreceptors and where are they found?

Answer 6

1. They are receptors that detect a change in blood pressure.
2. They are found in the aorta and carotid arteries.

Question 7

How do the baroreceptors and chemoreceptors react in response to high pressure, high oxygen concentration and low carbon dioxide concentration in the blood ( high pH)?

Answer 7

1. The baroreceptors detect the increase in pressure. The chemoreceptors detect an increase in oxygen and a decrease in carbon dioxide in the blood. There is less acidic carbon dioxide in the blood so the pH levels are higher.
2. They send more electrical impulses to the medulla.
3. The medulla sends an electrical impulse down the parasympathetic neurone.
4. The parasympathetic neurone releases acetylcholine, which binds to receptors on the cell membrane in the cells of the SAN.
5. This causes the SAN to slow the heart rate.
6. This means the blood pressure decreases, and since the blood is flowing more slowly, the cells have time to take in the oxygen for respiration and release carbon dioxide back into the blood. This puts the pH levels back to normal.

Question 8

How do the baroreceptors and chemoreceptors react in response to low blood pressure, low oxygen concentration and high carbon dioxide concentration in the blood ( low pH)?

Answer 8

1. The pH is lower because there is a higher concentration of acidic carbon dioxide and less oxygen in the blood. The chemoreceptors detect this and send more electrical impulses to the medulla. The baroreceptors also detect the decrease in pressure and send more impulses to the medulla.
2. The medulla sends an electrical impulse down the sympathetic nervous system which releases noradrenaline.
3. The noradrenaline binds to receptors on the SAN causing it to increase the blood pressure.
4. This allows for the faster removal of carbon dioxide from the blood and for the blood and the oxygenation of blood.

Question 9

Why is the cardiac muscle described as myogenic?

Answer 9

It contracts and relaxes without external stimulation from the nervous or endocrine system.

Question 10

What is the role of the SAN, AVN, the bundle of his and the outline fibres in controlling the myogenic stimulation of the heart?

Answer 10

1. The SAN sends out a wave of depolarisation across the atria causing it to contract.
2. When this wave reaches the AVN it will send out another wave of depolarization.
3. There is a non-conductive layer between the atria and ventricles which prevents the waves of depolarisation from going into the ventricles.
4. The wave of depolarisation travels down the bundle of his and into the Purkinje fibres in the walls of the ventricles
5. This causes the ventricles to contract from the bottom up.
6. This shirt delay between the atria and ventricles contracting allows the blood to flow into the ventricles so it can be pumped into the arteries.