Control of Heart Rate

Question 1

What two systems is the nervous system split up into?

Answer 1

The central nervous system

The peripheral nervous system

Question 2

What is the CNS made up of?

Answer 2

Brain and spinal cord

Question 3

What is the peripheral nervous system made up of?

Answer 3

The neurones that connect the CNS to the rest of the body

Question 4

What are the two different systems within the peripheral nervous system?

Answer 4

The somatic

The autonomic nervous systems

Question 5

What does the somatic nervous system control?

Answer 5

Conscious activities, e.g running and playing video games

Question 6

What does the autonomic nervous system control?

Answer 6

Unconscious activities, e.g digestion

Question 7

What is the autonomic nervous system split into?

Answer 7

The sympathetic and the parasympathetic nervous systems.

Question 8

What is the general difference between the sympathetic nervous system and the parasympathetic nervous system?

Answer 8

The sympathetic nervous system is the fight or flight system that gets the body ready for action.
The parasympathetic nervous system is the rest and digest system that calms the body down.

Question 9

What does the SAN do?

Answer 9

Generates electrical impulses that cause the cardiac muscles to contract.

Question 10

What controls the rate at which the SAN fires?

Answer 10

The medulla

Question 11

What causes fainting?

Answer 11

Low blood pressure

Question 12

What are internal stimuli detected by?

Answer 12

Pressure receptors and chemical receptors

Question 13

What are baroreceptors?

Answer 13

Pressure receptors in the aorta, the vena cava and carotid arteries that are stimulated by high and low blood pressure.

Question 14

What are chemoreceptors?

Answer 14

Chemical receptors in the aorta, the carotid arteries and in the medulla. They monitor the O2 level in the blood and also CO2 and pH

Question 15

How does the heart respond to high blood pressure?

Answer 15

Baroreceptors detect high blood pressure.
They send impulses along sensory neurones to the medulla.
This sends impulses along parasympathetic neurones.
These secrete acetylcholine, which binds to receptors on the SAN.
This causes the heart rate to slow down in order to reduce blood pressure.

Question 16

How does the heart respond to low blood pressure?

Answer 16

Baroreceptors detect low blood pressure.
They send impulses along sensory neurones to the medulla.
This sends impulses along sympathetic neurones.
These secrete noradrenaline, which binds to receptors on the SAN.
This causes the heart rate to speed up in order to increase blood pressure.

Question 17

How does the heart respond to high blood O2, low CO2 or high blood pH levels?

Answer 17

Chemoreceptors detect chemical changes in the blood. They send impulses along sensory neurones to the medulla.
This sends impulses along parasympathetic neurones.
These secrete acetylcholine, which binds to receptors on the SAN.
This causes the heart rate to decrease in order to return O2, CO2 and pH levels back to normal.

Question 18

How does the heart respond to low blood O2, high CO2 or low blood pH levels?

Answer 18

Chemoreceptors detect chemical changes in the blood.
They send impulses along sensory neurones to the medulla.
This sends impulses along sympathetic neurones.
These secrete noradrenaline, which binds to receptors on the SAN.
This causes the heart rate to increase in order to return O2, CO2 and pH levels back to normal.

Question 19

What are the effects of exercise on cardiac output?

Answer 19

Increased muscular/metabolic activity.
More carbon dioxide produced by tissues due to increased respiration
Blood pH is lowered.
Chemical receptors in the carotid arteries increase frequency of impulses to the medulla oblongata.
Centre in the medulla oblongata that speeds heart rate, increases frequency of impulses to SA node via the sympathetic nervous system.
SA node increases heart rate.
CO2 levels return to normal.

Question 20

What is the passage of action potentials in the heart?

Answer 20

Action potentials originate in the sinoatrial node and travel across the wall of the atrium to the atrioventricular node.
They pass slowly through this to give the atria time to contract.
They then pass rapidly along the AV bundle which extends from the AV node through the fibrous skeleton to inter ventricular septum.
The atrioventricular bundle divides into right and left branches and action potentials descend rapidly to the apex of each ventricle along the bundle of His.
Action potentials are carried by the purkynje fibres from the bundle branches to the ventricular walls.

Question 21

Flow of blood through the heart

Answer 21

Right atrium -> right ventricle -> pulmonary artery -> lungs -> pulmonary vein -> left atrium -> left ventricle -> aorta -> organs -> veins -> vena cava -> right atrium