1. Some Most All Control of heart rate WAL:
An overview of how the heart rate is controlled
WAL:
All
Most
What role do chemical and pressure receptors play in the process?
Some
How does the autonomic nervous system control heart rate?
What is the autonomic nervous system?
Starter – If the hormonal system and nervous system had a fight who would win and why?

2. Today we are covering from the specification:
Pages of your textbook

3. The Nervous System
Divided into two systems:
The CNS – brain and spinal cord
The Peripheral Nervous System (PNS) – pairs of nerves

4. Nervous system Nervous system Peripheral Nervous system Central
Brain
Spinal cord
Sensory
system
Motor system
Voluntary system
Autonomic system
Sympathetic
Parasympathetic

5. Control of Heart Rate Autonomic Sympathetic Parasympathetic Inhibitory
(slows down activity)
Positive stimulation
(speed up activity)

6. Control of heart rate
Heart rate is controlled by the part of the brain called the medulla oblongata
Has two centres:
Increases heart rate linked to the sinoatrial node by the sympathetic nervous system
Decreases heart rate linked to the sinoatrial node by the parasympathetic nervous system
The centre that is stimulated depends on:
Chemical changes in the blood
Pressure changes in the blood

7. Control by chemoreceptors
Found in the walls of the carotid artery
Sensitive to changes in the pH of the blood that result from changes in carbon dioxide concentration. (In solution CO2 forms an acid)

8. Control by chemoreceptors
When the blood has a higher than normal concentration of CO2, pH decreases.
Chemoreceptors in the wall of the carotid arteries and the aorta detect this and increase the frequency of nervous impulses to the centre in the medulla oblongata that increases heart rate.
This centre increases the frequency of impulses via the sympathetic nervous system to the sinoatrial node, increasing heart rate.

9. Control by chemoreceptors
The increased blood flow that this causes leads to more CO2 being removed in the lungs and so the CO2 levels return to normal
As a consequence the pH of the blood rises to normal and the chemoreceptors in the wall of the carotid arteries and aorta reduce the frequency of nerve impulses to the medulla oblongata.
The medulla oblongata reduces the frequency of impulses to the sinoatrial node, which therefore decreases the heart rate to normal.

10. Control by pressure receptors
Pressure receptors occur within the walls of the carotid arteries and the aorta. They operate as follows:
When a blood pressure is higher than normal:
1) They transmit a nervous impulse to the centre of the medulla oblongata that decreases heart rate.
2) This centre sends impulses via the parasympathetic nervous system to the sinoatrial node of the heart, decreasing heart rate.

11. Control by pressure receptors
Pressure receptors occur within the walls of the carotid arteries and the aorta. They operate as follows:
When a blood pressure is lower than normal:
1) They transmit a nervous impulse to the centre of the medulla oblongata that increases heart rate.
2) This centre sends impulses via the sympathetic nervous system to the sinoatrial node of the heart, increasing heart rate.

12. Modifying heartbeat Carotid artery Chemo receptors Pressure receptors
hypothalamus
medulla
Sinoatrial node
Atrioventricular node
Vagus nerve
Cardioinhibitory centre
Cardioacceleratory centre
Human circulation

13. Plenary– Answer the questions on page 149
Control of heart rate
An overview of how the heart rate is controlled
WAL:
All
Most
What role do chemical and pressure receptors play in the process?
Some
How does the autonomic nervous system control heart rate?
What is the autonomic nervous system?
Plenary– Answer the questions on page 149