What happens to the brain during a concussion?

A direct or indirect blow to the head, face or jaw can cause the brain to accelerate then rapidly decelerate within the skull. This acceleration/deceleration motion can induce mechanical changes to the nerve fibres – causing them to stretch – and in turn, alter several important metabolic pathways. Though injury is apparent given the spectrum of symptoms experienced by a concussed athlete, no structural damage is caused to the brain itself. That is, unlike other sports injuries (like a fractured wrist or dislocated shoulder) nothing appears abnormal on standard imaging studies like CT, or MRI. Instead, these imaging methods are used to rule out more severe trauma such as bleeding within the brain or skull or fractures of the skull or neck. We understand now, more than ever, that just because we can’t see the injury, it doesn’t mean that something’s not wrong.

Current evidence suggests that the rapid stretch of nerve fibres within the brain during a concussive trauma results in the release of various neurotransmitters (signalling molecules within the brain), which trigger the initiation of a complex neurometabolic pathway. Ultimately an energy crisis ensues, and the brain is unable to produce the energy required to sustain its normal processes. These changes take place within minutes of the injury and can last for hours or days before normalization occurs.It is thought to be this metabolic imbalance, along with other impaired physiological processes that contribute to the physical, cognitive, behavioural and emotional signs and symptoms typically seen in a concussed individual.