Understanding Stroke
A stroke is a brain attack – a sudden interruption of blood flow to a part of the brain, causing it to stop working and eventually damage brain cells. The effects can be devastating and may last a lifetime.
The Brain
The brain is the control centre, like an intricate computer controlling the body. The brain’s nerve cells are connected to other nerve cells in every part of the body. Some of these cells send messages to the brain, telling it what is happening throughout the body. Others carry messages from the brain to tell the various body organs and systems how to function. Some brain cells enable memories, personality, and our ability to communicate or make decisions.
Blood Supply
Like any other part of your body, your brain needs a constant supply of blood and oxygen for it to work. The vessels that carry the blood are a system of tubes of various sizes. Each area of the brain has its own blood supply from one of these branches.
- Arteries bring blood full of oxygen from the heart and lungs to the brain (and other organs)
- Veins take the used blood back to the heart and lungs so that oxygen levels can be restored
- Capillaries are a network of tiny blood vessels that join up the arteries and veins. Here the oxygen can easily travel from the blood to the brain cells where it is needed.
How a Stroke happens
There are two main ways a stroke happens: either a clot blocks a blood vessel in the brain, or a blood vessel in the brain bursts.
1. Ischaemic Stroke – a blocked blood vessel in the brain.
This is the most common type of stroke. When the blood supply is blocked or insufficient, the section of the brain supplied by that artery does not receive the oxygen it needs to function and brain cells are damaged. The blockage to the artery happens because:
- Disease (atherosclerosis or ‘hardening of the arteries’) causes a build up of fatty tissue (plaque) in the wall of the artery. If the lining of these fatty deposits breaks, a clot can form and this narrows the space that blood can flow through or blocks the flow altogether.
OR
- An embolus, which is a blood clot or a clump of debris, breaks off and travels in the bloodstream until it becomes stuck in a small or narrowed artery in the brain. The embolus can come from one of the large blood vessels between the heart and the brain or from the heart itself. For example, this can happen after a heart attack, or as a result of heart valve disease or an abnormal heart rhythm (especially atrial fibrillation [AF]).
2. Haemorrhage – a burst blood vessel causes bleeding in the brain
There are two main types of brain haemorrhage – intra-cerebral haemorrhage and subarachnoid haemorrhage.
- Intra-Cerebral haemorrhage
This is when blood bursts through the walls of an artery and leaks into the brain. This can happen because the person was born with a faulty artery or an abnormal collection of blood vessels, or because disease (usually caused by high blood pressure) has weakened the artery walls. The leaking blood is forced into brain tissue causing damage. Because there is little space inside the skull cavity, the build up of blood also presses on nearby parts of the brain causing further damage to nerve cells and brain function. Only 10 – 15 per cent of strokes are due to haemorrhage. - Aneurysms and sub-arachnoid haemorrhage
An aneurysm is when a weakness in an artery wall balloons out and forms a thin walled bubble on the artery. If the bubble (aneurysm) bursts, the blood leaks into the fluid surrounding the brain, usually resulting in a sudden severe headache. Sometimes the increased pressure inside the skull makes people drowsy or even unconscious. Aneurysms may develop over several years and usually don’t cause detectable problems until they burst.
Stroke Foundation of N.Z. Inc (National office)
P O Box 12482
L1, Federation House
95-99 Molesworth Street
WELLINGTON
Tel: 04 472 8099
0800 STROKE (0800 78 76 53)
E-mail: strokenz@stroke.org.nz
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