Medical Definition of Concussion of the brain

Reviewed on 3/29/2021

Concussion of the brain: A traumatic injury to the brain as a result of a violent blow, shaking, or spinning. A brain concussion can cause immediate and usually temporary impairment of brain function such as of thinking, vision, equilibrium and consciousness.

Although anyone can have a concussion, we will focus here purely for purposes of example on athletes who suffer a concussion. The considerations can be generalized to the general population of people with concussions of the brain.

Objective signs of concussion: The signs of concussion observed by medical staff in athletes with a concussion, according to The American Medical Association (AMA), include the following:

  • Player appears dazed
  • Player has vacant facial expression
  • Confusion about assignment
  • Athlete forgets plays
  • Disorientation to game or score
  • Inappropriate emotional reaction
  • Player displays clumsiness
  • Player is slow to answer questions
  • Loss of consciousness
  • Any change in typical behavior

Subjective symptoms of concussion: The symptoms of concussion reported by athletes with a concussion, according to the AMA, include the following:

  • Headache
  • Nausea
  • Balance problems or dizziness
  • Double or fuzzy vision
  • Sensitivity to light or noise
  • Feeling slowed down
  • Feeling "foggy" or "not sharp"
  • Change in sleep pattern
  • Concentration or memory problems
  • Irritability
  • Sadness
  • Feeling more emotional

Causes: A concussion is not a bruise to the brain caused by hitting a hard surface. In fact, no physical swelling or bleeding is usually seen on radiological scans.

Impact: The concussion occurs from impact when the head accelerates rapidly and then is stopped, or from spinning when the head is spun rapidly and then is stopped. Impact to the brain can occur when the head slams into a hard surface. The skull is stopped by the hard surface but the brain, floating in cerebrospinal fluid (CSF), can still move and is shaken.

Spinning: Spinning of the brain can occur when a blow causes the head to snap rapidly. The skull then stops spinning but the brain, floating in cerebrospinal fluid (CSF), can still move and is damaged.

Violent trauma: Violent trauma, whether it be from shaking or spinning, causes the brain cells to become depolarized and fire all their neurotransmitters at once in an abrupt cascade, flooding the brain with chemicals --there is a sudden flood of ions (including sodium, potassium, and calcium) -- and deadening receptors in the brain that are associated with learning and memory.

Second impact syndrome: Sometimes a person has a second concussion before their brain has recovered from the first. This can lead to what is called second impact syndrome. In the second impact syndrome, massive swelling of the brain causes pressure inside the skull that chokes off the flow of fresh blood and leads to irreparable brain damage or death.

Recovery from concussion: It takes considerable time and energy for the brain to correct this chemical imbalance. Changes in the brain start to resolve immediately, but the recovery time seems to vary. The time depends not only on the severity of the blow, but also on how many previous concussions a person has had.

After a concussion, the arteries in the brain constrict. This reduces blood flow to the brain and lowers the rate at which oxygen is delivered to the brain. At the same time the demand rises for the sugar glucose which provides energy to the brain for healing. But the need for more glucose cannot be met by the narrowed arteries and this discrepancy ("mismatch") creates a metabolic crisis. Eventually the damaged brain cells (that survive) do slowly repair themselves, the demand for glucose eases, the arteries to the brain open wider, and blood flow to the brain returns to normal. However, the brain stays in a lowered metabolic state, a quiescent condition, for a considerable length of time before it can return to normal.

Return to normal activities: The American Academy of Neurology has established guidelines for athletes with concussion returning to play. The guidelines divide concussions into three grades of severity, with a prolonged knockout being the worst. The Academy recommends that athletes whose symptoms -- headaches, nausea, amnesia, blurred vision -- do not clear up within 15 minutes, or who lose consciousness even briefly, be kept out of competition until their symptoms have disappeared completely for at least a week.

Susceptibility to future concussions: Once a person has had a concussion, he or she is as much as four times more likely to sustain a second one. Moreover, after several concussions, it takes less of a blow to cause the injury and requires more time to recover.



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