Control of the heart rate

Question 1

What makes up the nervous system?

Answer 1

1. CNS- the brain and spinal cord.
2. The peripheral nervous system- all the neurones that connect the CNS to the rest of the body.

Question 2

What makes up the peripheral nervous system?

Answer 2

1. The somatic nervous system- responsible for conscious actions.
2. The automatic nervous system- responsible for unconscious action.

Question 3

What makes up the automatic nervous system?

Answer 3

1. sympathetic nervous system- gets the body ready for action.
2. parasympathetic nervous system- slows the body down.

Question 4

Why is the cardiac muscle considered myogenic?

Answer 4

It can contract without receiving signals from nerves.

Question 5

How is the heartbeat controlled?

Answer 5

1. The SAN sends waves of electrical activity along the walls of the atria causing them to contract.
2. The waves of electrical activity travel to the AVN which sends them down the bundle of His.
3. There is a slight delay before the AVN does this to make sure the atria have emptied before the ventricles contract.
4. The bundle of His then takes the waves of electrical activity down the apex of the heart and into the Purkinje fibres.
5. The Purkinje fibres take the waves of electrical activity to the walls of the ventricles causing them to contract from the bottom up.

Question 6

What controls the rate at which the SAN fires waves of electrical activity?

Answer 6

The medulla

Question 7

What are the receptors involved in the control of the heart rate?

Answer 7

1. Baraoreceptors in the aorta and carotid arteries detect a change in blood pressure.
2. Chemoreceptors in the medulla and carotid arteries detect a change in the pH.

Question 8

Describe what happens when the blood pressure is high.

Answer 8

The baroreceptors in the aorta and carotid arteries detect the increase in blood pressure and send an impulse along the sensory neuron to the medulla. The medulla then sends an impulse down the parasympathetic neurone which releases acetylcholine. The acetylcholine binds to receptors on the walls of the SAN which causes the heart rate to slow. This then decreases the blood pressure

Question 9

Describe what happens when the blood pressure is low.

Answer 9

The baroreceptors in the aorta and carotid arteries detect the decrease in blood pressure and send an impulse along the sensory neurone to the medulla. The medulla then sends an impulse down the sympathetic neurone which releases noradrenaline. The noradrenaline binds to receptors on the walls of the SAN which causes the heart rate to increase. This then increases the blood pressure.

Question 10

Describe what happens when the blood pH is high ( High O2 concentration and low CO2 concentration).

Answer 10

The chemoreceptors in the medulla and carotid arteries detect an increase in oxygen concentration in the blood and send a message along the sensory neurone to the medulla. The medulla then sends a message down the parasympathetic neurone, The parasympathetic neurone releases acetylcholine which binds to the walls of the SNA. This causes the heart rate to slow down so the oxygen can be used up by respiring cells and carbon dioxide can be released. This decreases the pH levels back to normal.

Question 11

Describe what happens when the blood pH is low ( low O2 concentration and high CO2 concentration).

Answer 11

The chemoreceptors in the medulla and carotid arteries detect a decrease in oxygen concentration in the blood and send a message along the sensory neurone to the medulla. The medulla then sends a message down the sympathetic neurone, The sympathetic neurone releases noradrenaline which binds to the walls of the SNA. This causes the heart rate to speed up so carbon dioxide can be removed quickly and more oxygen can diffuse into the blood in the lungs.