Crash: Self-defence - text only -

• Raising the alarm

• Emergency repairs

• Programmed to survive

• Coma

• Neurogenesis

• Relocation

• Raising the alarm
When the senses perceive a possible threat to the body, electrical impulses are sent racing up the spine to convey the threat to the brain. The first stop for all incoming signals to the brain is the thalamus, a neural waystation, which sends them out to the parts of the brain that need to receive them.

When danger signals arrive at the thalamus, it sends a message straight to the amygdala, the part of the brain that controls defensive behaviour, setting the body to high alert. The thalamus also routes the danger signals to the analysing front area of the brain, which decides whether or not you need to react in a defensive way to your surroundings. If this part of the brain decides that the body needs to prepare itself for a threat, it sends another signal to the amygdala.

The amygdala prepares the brain and body to react quickly to danger. The heart beats faster, increasing the blood supply to the brain and other organs; the blood pressure increases; and stress hormones are produced, giving the body the ability to respond rapidly.

Amazingly, your brain can also suppress your capacity to feel pain, so that you can continue to defend yourself even if you are hurt.

All these physical effects are accompanied by a feeling of fear.

• Emergency repairs
Once injured, the body immediately sets about healing itself. Its first reaction is a momentary constriction of the blood vessels in the damaged area, followed by a dilation that sends vital blood to the wound. At the same time, the walls of the blood vessels allow protein-rich fluids to exit into the injured tissue. These fluids include cells that fight infection and clean up the cell debris from the wound. The flooding of fluid into the damaged area causes it to swell, triggering pain receptors.

But if the injury is to the brain, the flooding response may not help the situation. The brain is surrounded by the skull, if it is swamped with fluid, its cells are squeezed. As the pressure increases in the brain, it becomes difficult for blood to reach damaged areas, and the brain will be starved of the oxygen and glucose that it needs.

• Programmed to survive
But the brain has strategies to cope with threats to its own survival — and therefore the survival of the whole individual — such as the loss of blood supply. It prioritises its own survival over that of the rest of the body, and it prioritises one part of itself over all else: the brain stem.

In evolutionary terms, the brain stem is the oldest part of the brain. It runs our bodies without our conscious awareness. When we sleep, parts of the brain are turned off, but the brain stem never sleeps. It sends out electrical messages that control the heartbeat, breathing, circulation and digestion. Damage to the brain stem can affect its ability to control these activities and they may stop, leading to death.

In the case of an injury that disrupts the flow of blood to the brain or shatters its circuitry, such as the trauma that David suffers, the brain stem will shut down every part of the brain not vital to survival within 8 to 10 seconds of loss of blood supply. It can then divert all the blood available to its own cells so that it can carry out the body's most crucial reflexive functions. However, if the blood supply is not restored, the brain stem itself will die after about three minutes.

A person whose brain has shut down to only its reflexive functions is in a coma.

• Coma
Coma is rarely a state of total vegetation. Unconsciousness may be so deep that no amount of stimulation will cause a person to respond. But in many cases, a person in a coma can move, make noises and respond to pain.

Coma is the body's way of coping with the most serious threats to its survival. While in a coma the brain may be able to repair itself (see Neurogenesis below) and other cells in the body can regenerate while the body and brain are at rest.

It is widely believed that prolonged coma implies that, if a person wakes, their chances of recovery are poor. In fact, some people who have been in a prolonged coma make a full recovery. Others may suffer disabilities, and in some cases, they emerge from coma only to a PVS (persistent vegetative state). In PVS, a patient may appear to be awake: they may open their eyes and look about the room, but they are otherwise unresponsive. It is possible to recover from PVS, but the longer a person remains in this state, the poorer their chances of recovery become.

• Neurogenesis
Recently, scientists have discovered that the brain can grow new cells through a process known as neurogenesis. If scientists can learn enough about this process, they may be able to use their knowledge to help the brain heal itself.

On its own the brain cannot re-grow enough cells to repair itself completely after a severe trauma, though it may be able to re-establish some connections between neurons. During this vital and delicate process the brain keeps the body immobile in a coma.

• Relocation
Another mysterious way in which the brain resurrects itself after trauma is through the re-distribution of the brain's workload from damaged areas to healthy areas of the brain. In this way, an individual may recover lost functions despite permanent brain damage. However, crucial, fragile connections between neurons must still be able to function to pass messages on, or must be regenerated to do so.

Trauma | Self-defence | Intervention

Amnesia | Car safety

top

Crash | Teen dreams | Fat attack

Brave new world | Bad taste | Allergy

Home | Find out more | Glossary | Credits