The Autonomic nervous system
Controls subconscious activities of muscles and glands
two main divisions:
1.) The sympathetic nervous system – Speeds up activities and thus allows us to cope with stressful situations (fight or flight response).
2.) The parasympathetic nervous system – Inhibits effects and slows down activities. This allows energy to be conserved. Controls under normal resting conditions.
The two divisions are antagonistic, meaning that their effects oppose one another.
Changes of the heart rate are controlled by a region of the brain called the medulla, which has two main divisions:
- One division is connected to the sino-atrial node through the sympathetic nervous system.
- The other is connected to the sino-atrial node via the parasympathetic nervous system.
Control by chemoreceptors
Chemoreceptors are found in the wall of the carotid arteries and detect changes in pH as a result of CO2 concentration.
When CO2 concentration in the blood is too high, chemoreceptors detect the drop in pH and send impulses to the section of the medulla oblongata responsible for increasing heart rate.
This section then increases the number of impulses sent to the S.A node via the sympathetic nervous system.
This results in an increase in heart rate, which then causes blood pH to return to normal.
Control by pressure receptors
Pressure receptors occur in the wall of the carotid arteries and the aorta.
When blood pressure is too high – impulses are sent to the medulla oblongata which then sends impulses to the S.A node via the parasympathetic nervous system decreasing the heart rate.
When blood pressure is too low – impulses are sent to the medulla oblongata which then sends impulses to the S.A node via the sympathetic nervous system, increasing the heart rate.