The autonomic nervous system controls the involuntary activities of internal muscles and glands. It has two divisions:
- the sympathetic nervous system. This stimulates effectors and so speeds up any activity. It helps us to cope with stressful situations by heightening our awareness and preparing us for activity (the fight or flight response).
- the parasympathetic nervous system. This inhibits effectors and so slows down any activity. It controls activities under normal resting conditions. It is concerned with conserving energy and replenishing the body's reserves.
The actions of the sympathetic and parasympathetic nervous systems normally oppose eachother - they are antagonistic.
Changes to the heart rate are controlled by a region of the brain called the medulla oblongata. This has two centres:
- a centre that increases heart rate, which is linked to the sinoatrial node by the sympathetic nervous system
- a centre that decreases heart rate, which is linked to the sinoatrial node by the parasympathetic nervous system
Control by Chemoreceptors
Chemoreceptors are found in the wall of the carotid arteries…