Concussion is the most common traumatic brain injury
A concussion can follow a blow to the head or a jolt elsewhere on the body that whips the skull. Headache leads the list of symptoms, with dizziness, foggy thinking, poor sleep, brief memory gaps and mood swings close behind. Each year more than 3.5 in every 1,000 people worldwide are thought to suffer one.
Doctors class concussion as a mild traumatic brain injury, and it is the most common kind. Men and young adults are hit most often, usually through car crashes, falls, sport or bicycle accidents; violence, alcohol and a previous concussion all raise the risk. Symptoms generally show up within 72 hours, most often in the first minutes or hours, though some are delayed. Being knocked out briefly does not by itself signal a worse injury.
The brain floats in cerebrospinal fluid, which absorbs light knocks but not hard impacts or sudden acceleration. The skull can push the brain in straight lines, spin it around its centre of gravity, or twist it on another axis, and the twisting kinds do the most harm in the midbrain and diencephalon. Disruption of the arousal network housed there is the leading explanation for loss of consciousness. Studies of athletes up to 2007 found that neither the size nor the location of an impact reliably predicted how bad a concussion would be.
What follows is chemical as much as mechanical. Nerve cells release a flood of excitatory messengers such as glutamate, ions slip out of balance, and blood flow to the brain drops somewhat, though less than in a stroke. Cells then face an energy shortage, their mitochondria slow, and they fall back on less efficient metabolism that leaves lactate behind. For minutes to days afterwards the brain is unusually fragile to swings in pressure, blood supply or oxygen.
The injury is spread across the brain rather than focused in one spot, and researchers still argue whether it is purely a disturbance of function or involves structural damage. Prevention leans on helmets and mouth guards in some sports, seatbelts, rules on body contact, and neuromuscular warm-ups. Most people recover well.
Source: Concussion
