What happens in your body?Putting energy into digesting your lunch, optimising your immune system or ensuring you are fertile all become rather unimportant in life-threatening situations. All these non-essential body functions cease and you divert all energy to your muscles and brain.
Your heart beats faster, your blood pressure increases and you breathe faster pumping maximum oxygen and energy-rich blood to your muscles. Your liver releases more sugar into your blood ready for action.
Most other situations are subjective. Life-events, exams or types of work can be hugely stressful to one person yet easier to cope with by others.
As with many forms of perception, scientists don’t know the actual neural mechanisms that allow you to combine your prior experience with information coming in through your senses, and produce your brains judgement that a situation is dangerous.
What happens in your brain?
Once your brain has decided there’s a danger, it sends immediate nerve signals down your spinal cord to your adrenal glands telling them to release the hormone adrenaline. Once released, adrenaline increases the amount of sugar in your blood, increases your heart rate and raises your blood pressure (and has many other actions).
Your brain’s remarkable hypothalamus also sends signals to your pituitary gland at the bottom of your brain, telling it to release factors that within a few minutes have travelled through your blood stream and stimulated your adrenal cortex to produce a stress hormone – cortisol.
Long-term effects of stress
Your body’s stress response is perfect in the short-term, but damaging if it goes on for weeks or years. Raised levels of cortisol for prolonged periods can damp down your immune system and decrease the number of brain cells so impairing your memory. It can also affect your blood pressure and the fats in your blood making it more likely you will have a heart attack or stroke.
|Cortisol has been shown to damage and kill cells in the hippocampus (the brain area responsible for your episodic memory) and there is robust evidence that chronic stress causes premature brain aging. |
Without cortisol you would die – but too much of it is not a good thing. It seems it makes your brain more vulnerable to damage such as strokes, ageing and stressful events.
Stress and depression
It's quite clear that chronic stress is related to depression.A common feature of depression is an excess release of cortisol into the blood. Some neuroscientists and psychiatrists are now suggesting that the major changes in serotonin and other neurotransmitters seen in depression are not the cause of depression, but secondary to changes in the stress response.