Factors that affect the Cardiac conduction system

Question 1

The cardiac control centre

Answer 1

• The cardiac control centre is located in the medulla oblongata.
• Here, HR is controlled by 2 systems:
  1. Sympathetic nervous system:
  
  • Sympathetic nerve impulses increase HR.
  • More impulses= increased HR.

2. Parasympathetic nervous system:
   - Parasympathetic nerve impulses decrease HR.
   - Less impulses= decreased HR.

Question 2

What receptors stimulate the cardiac control centre?

Answer 2

• The cardiac control centre is stimulated by 3 main receptors.

1. Chemoreceptors
2. Baroreceptors
3. Proprioceptors

Question 3

Chemoreceptors (chemical)

Answer 3

1. Exercise begins
2. Chemoreceptors detect a rise in carbon dioxide in the blood (increased acidity).
   - During exercise more CO2 is produced as a result of more O2 being consumed and utilised.
3. This info is sent to the medulla oblongata.
4. As a result the sympathetic nervous system is stimulated.
5. Increased impulses are sent to the SAN.
6. Heart rate increases to match the demands of exercise.

Question 4

Baroreceptors (neural)

Answer 4

• Baroreceptors detect changes in blood pressure (the stretching of arterial walls).

1. The baroreceptors detect a drop in blood pressure.
2. This info is sent to the medulla oblongata.
3. The sympathetic nervous system is stimulated.
4. Increase signals are sent to the SAN.
5. HR increases to increase blood pressure.

Question 5

Baroreceptors pt.2

Answer 5

• The opposite happens if the baroreceptors detect an increase in blood pressure (parasympathetic NS stimulation/ decreased signals to the SAN/ decrease HR/ decreased blood pressure).

Question 6

Baroreceptors and exercise

Answer 6

Baroreceptors set limits in relation to what the body is doing.
- At rest blood pressure is set to a certain level to maintain a healthy blood pressure.
- However, during exercise this set level has to be increased as blood pressure will obviously rise as a result of the increased HR and O2 demands.

• If the limit was not changed during exercise HR would be lowered during exercise which would result in less oxygen getting to the working muscles.

Question 7

Proprioceptors

Answer 7

• Proprioceptors detect movement in the body.
• They are located in the muscles, joints and tendons.

1. During exercise, proprioceptors detect an increase in muscular movement.
2. This information is then sent to the medulla oblongata.
3. This then stimulates the sympathetic nervous system.
4. Increased signals are sent to the SAN.
5. Heart rate increases to meet the demands of the exercise.

Question 8

Hormonal control

Answer 8

• During exercise adrenaline/ noradrenaline is released.
• This is known as hormonal control.

1. Exercise begins.
2. Adrenaline is released.
3. This info is sent to the medulla oblongata.
4. The sympathetic nervous system is then stimulated.
5. As a result increased impulses are sent to the SAN.
6. Heart rate increases to meet the demands of the exercise.