What is a concussion?

A concussion is the bruising of the brain. Peter Holmes, MD, with Methodist Ambulatory Surgery Hospital, talks about the severity of a concussion and how to detect it.
A concussion is an injury to the brain caused by a bump to the head or body that shakes the brain. This causes damage to the nerve cells of the brain and keeps them from working normally for a while. You can’t see a concussion on a computerized tomography (CT) scan, magnetic resonance imaging (MRI) or x-ray. A concussion is diagnosed by knowing the signs or symptoms that show up after injury to the head. A sign is something that you can see when looking at a child with a concussion (they seem dazed or confused, for example). A symptom is what they are telling you they feel, such as headache or dizziness.   
Todd Brubaker, DO
Pediatrics
A concussion is a type of traumatic brain injury (TBI) caused by a bump, blow or jolt to the head or by a high-speed hit to any part of the body that causes the head and brain to move rapidly back and forth. This sudden movement can cause the brain to bounce around or twist inside the skull, stretching and damaging the brain cells and creating chemical changes in the brain. This is called a coup-countrecoup injury. Disturbance of brain function is related to these chemical changes and is typically not seen with any imaging like a CT scan or MRI.
 
Concussions are a brain injury similar to scrambling an egg inside its shell or a bruised banana. You can think of it like a "brain sprain." Like muscle sprains, concussions vary in severity, from mild to moderate to severe. Considered a mild traumatic brain injury, a concussion can last hours, days, or even weeks. If the symptoms of a concussion continue beyond a week or two, the severity may increase to post-concussion syndrome or even mild traumatic brain injury (mTBI). Resting alone may not be enough and can actually lead to long-term negative consequences.
UCLA Health
Administration

A concussion is a traumatic brain injury resulting in neurological dysfunction caused by a bump or blow to the head. It may or may not involve a loss of consciousness.

A concussion is a type of traumatic brain injury that can occur with a blow or jolt to the head, which can cause the brain to move back and forth inside the skull. Usually they are not life-threatening, but caution needs to be taken when one occurs because repetitive injury to the brain can cause long-term effects. If you think that you or someone you know has had a concussion, please see a doctor immediately. Signs to watch for are irritability, sleepiness, headache, and confusion.
A concussion is a brain injury caused by a blow to the body that causes the brain to shake inside the skull. This event leaves the brain damaged, which hinders its performance.

(This answer provided for NATA by the Washington State University Athletic Training Education Program.)
American Red Cross
Administration
A concussion is a type of brain injury that involves a temporary loss of brain function resulting from a blow to the head.

A person with a concussion may not always lose consciousness. The effects of a concussion can appear immediately or very soon after the blow to the head and include sleep, mood, and cognitive disturbances, and sensitivity to light and noise.

However, some effects do not appear for hours or even days and may last for several days or even longer.
Intermountain Healthcare
Administration
A concussion is a type of brain injury. Swelling and bleeding are not involved. It cannot be seen on CT scan or traditional MRI, but is a dysfunction of brain metabolism. Most often it is caused by an impact injury to the head, but can also be caused by whiplash forces on the brain. Loss of consciousness is not necessary, but can occur. Common symptoms can be headache, nausea, sensitivity to light and noise, fatigue, memory loss, trouble with concentration, insomnia, decreased energy, dizziness, or becoming more emotional. Every concussion is different. Some last less than a week and others can have long-term effects. 

The basis of treatment is rest for the injured brain. This can include rest from physical, metal, visual, auditory, and emotional stimulation. Returning to activity or sports too soon can prolong the concussion or have more serious effects. In teenagers, returning to contact sports too soon has even caused serious brain injury or even death. This is called Second Impact Syndrome. Repetitive concussions, as sometimes seen in boxers or professional football linemen, can cause Chronic Traumatic Encephalopathy. This is a syndrome with degenerative changes in the brain that can be seen on CT scan or MRI. It is associated with depression, substance abuse, personality changes, headaches, movement problems, chronic mental deficiencies and even violence.

Research defines a cerebral concussion to be an abrupt loss of consciousness following a traumatic blow to the head. This sudden acceleration/deceleration force to the head causes the brain to hit the inside of the skull resulting in damage to the brain tissue. Depending on the severity of the impact, the damage can range from minimal to severe (possibly resulting in coma or death). The damage can also result in a hematoma (bleeding), which may cause harmful pressure on the brain. Sustaining multiple concussions (like in boxing) may lead to more chronic and severe conditions like traumatic encephalopathy (punchdrunk syndrome), which is characterized by weakness of the legs, tremors, altered speech, and slowed mental processes.

A concussion is a minor injury to the brain, which usually results from some type of trauma to the head. People who suffer a concussion may lose consciousness for a short period of time, suffer headaches, or experience other cognitive difficulties. Concussions are fairly common, especially among people who play contact sports, like football.

Continue Learning about Head Injuries

Head Injuries

Head Injuries

Some of the primary causes of head injuries are motor vehicle, bicycle, and motorcycle accidents and can result in concussions and contusions. Usually, people with serious head injuries lose consciousness. You may notice swelling ...

or broken bones in the skull. However, not all head injuries are obvious at first. Learn more about head injuries from our experts.
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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.