What happens to the brain when it’s injured?

Following a TBI a number of damaging changes occur within the brain. The severity of the injury determines the intensity and distribution of the various elements of the damage responses

What occurs during a traumatic brain injury?

Following the initial impact, the brain moves within the skull and can hit the opposite side of the skull from where the initial injury took place. The brain can also rotate within the skull causing stretch injury to the nerve cells. This leads to a cascade of events within the brain.

  • The concentration of some chemicals within the brain can change, and this, in turn, can trigger damage to specific cells and structures in the brain. Some of the harmful chemicals which can be produced in the brain after a TBI are called free radicals.
  • If there is a breach to the barrier between the brain and the rest of the body then this can allow inflammatory cells to enter the brain, and the inflammation which then occurs can result in worsening damage to the brain.
  • Nerve cells and the cells which make insulating myelin that protect the nerve cells can be disrupted. Nerve cells may be stretched or torn. While some of these nerve cells may rearrange and recover their function, others may die, leading to loss of brain connections and reduced function in that area of the brain.
  • The injured cells release molecules, which indicate that the host is in danger, initiating the infiltration of inflammatory cells to cause potential further local damage and also responses in the entire body.

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The degree of severity of these damage responses is a contributing factor in the symptoms someone suffers following a TBI.

Neurometabolic changes to the brain can also occur following a TBI, including an increase in glucose metabolism along with a decrease in cerebral blood flow. This can lead to an imbalance in energy supply and demand, and cause an array of additional symptoms including headache.1

The symptoms following a TBI are varied and range from mild to moderate to severe. The severity of symptoms is likely to be influenced by any pre-existing conditions that the person may have, the nature of the injury, the severity of the injury, where on the head the person was impacted, and the resulting area of the brain that was damaged – meaning that every TBI is different and complex.

Read about the symptoms of a Traumatic Brain Injury here.


  1. Gurley, James M., Hujsak, Bryan D., and Kelly, Jennifer L. ‘Vestibular Rehabilitation Following Mild Traumatic Brain Injury’. 1 Jan. 2013 : 519 – 528.
What is myelin?

Myelin is an insulating layer that covers the long processes of nerve cells within the brain and nervous system. It’s made up of protein and a fatty substance that allows nerve cells to more efficiently communicate with each other.

How does a free radical work?

When the brain is injured the concentration of some chemicals in specific cells or regions of the brain changes. The altered balance of chemicals can cause free radicals to occur. When a free radical is formed, it works to pull an electron from a molecule, which in turn makes that molecule a free radical. This can cause an unstable domino effect which causes disruption and further damage to the cells and structures of the brain.