Explainer: What is a concussion? | Science News for Students

Explainer: What is a concussion?

This severe type of head injury can damage a brain for weeks to years — perhaps a lifetime
Feb 15, 2018 — 6:25 am EST
soccer injury
A blow to the head can knock a player out of the game and might even cause a concussion.

It may start with a car accident. Or a collision with another athlete on the basketball court or soccer field. Perhaps a cheerleader did a header off a human pyramid. In each case, the end result is the same — a whopping knock to the noggin. If the hit was particularly hard, doctors may diagnose the individual with a concussion.

Its symptoms can include forgetfulness, headache, dizziness, fuzzy vision and sensitivity to noise. Some people may vomit. Others undergo behavioral changes. They might become irritable or have trouble concentrating. Severe concussions can even knock someone unconscious. People in this sleeplike state are not aware of their surroundings and experiences.

Concussion occurs when the brain slams against the inside of the skull. The brain’s parts are not uniform in size and density. So when this organ collides with bone, some parts of the brain will move faster than others. That can cause parts of the tissue to twist and get squashed. These movements can damage delicate nerve cells.

Those nerve cells, or neurons, are what relay signals inside our brains. They connect with each other through long, slender structures called axons. It’s these axons that a head injury can damage.

Just like a wire carries electricity, an axon carries electrical signals. Those signals tell other parts of the brain, or specific parts of your body, what to do. Without neurons to communicate information from your eyes to your brain, you wouldn’t be able to understand — or even see — the words in this sentence.

All those neurons in the brain form the control center for the body. That’s why the body has a skull: to protect the brain.

The skull forms a solid barrier between that control center and anything that might harm it. A cushion of fluid inside the skull surrounds the brain, further protecting it. This fluid keeps the brain from banging into the skull during normal activity. But extreme head movements can be too much for that cushion to handle. When the head snaps forward, back or to the side, the skull stops moving. The brain, however, may keep going — and smack hard against the bone.

When an axon is stretched or twisted, the cells to which it is a part may die. That’s why symptoms of concussion may last for weeks to months. More worrisome: Some changes may persist for years, emerging data show. These may escape the notice of patients and their doctors. For instance, the brain may seem to perform just fine, yet have to work unduly hard just to manage simple tasks. Such subtle changes may never go away.

Especially troubling is that repeated concussions in professional athletes — especially in boxers and football players — have been linked with permanent memory problems, even dementia. Many of those changes have been associated with a type of progressive brain disease known as CTE. That’s short for chronic traumatic encephalopathy (En-SEFF-uh-LOP-uh-thee).

A 2017 study of the brains of 202 former U.S. football players, all now deceased, showed 177 of them had developed CTE. The same condition also showed up in the brains of some younger athletes, including three of 14 high school football players and 48 of 53 college players.

Clearly, concussion is nothing to be ignored. Most experts now recommend weeks or months of recovery before a concussed athlete resumes activities that may pose a risk of being reinjured.

In a concussion, the brain bounces around inside the skull.
Centers for Disease Control and Prevention (CDC)/YouTube

Power Words

(more about Power Words)

axon     The long, tail-like extension of a neuron that conducts electrical signals away from the cell.

cell     The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall.

chronic traumatic encephalopathy (also known as CTE). This long-lasting brain disease is brought on by head injuries (often sustained in sports or military service). This disease often is progressive, meaning it worsens with time.

concussion     Temporary unconsciousness, or headache, dizziness or forgetfulness due to a severe blow to the head.

deceased     An adjective that describes someone who has died.

dementia     A type of mental disorder caused by disease or injury that causes people to gradually lose all or part of their memory. It may start out temporary and build to a permanent condition where the ability to reason also is impaired.

density     The measure of how condensed some object is, found by dividing its mass by its volume.

diagnose     To analyze clues or symptoms in the search for their cause. The conclusion usually results in a diagnosis — identification of the causal problem or disease.

electricity     A flow of charge, usually from the movement of negatively charged particles, called electrons.

high school     A designation for grades nine through 12 in the U.S. system of compulsory public education. High-school graduates may apply to colleges for further, advanced education.

nerve     A long, delicate fiber that transmits signals across the body of an animal. An animal’s backbone contains many nerves, some of which control the movement of its legs or fins, and some of which convey sensations such as hot, cold or pain.

neuron     An impulse-conducting cell. Such cells are found in the brain, spinal column and nervous system.

organ     (in biology) Various parts of an organism that perform one or more particular functions. For instance, an ovary is an organ that makes eggs, the brain is an organ that makes sense of nerve signals and a plant’s roots are organs that take in nutrients and moisture.

risk     The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)

skull     The skeleton of a person’s or animal’s head.

subtle     Some feature that may be important, but can be hard to see or describe. For instance, the first cellular changes that signal the start of a cancer may be visible but subtle — small and hard to distinguish from nearby healthy tissues.

symptom     A physical or mental indicator generally regarded to be characteristic of a disease. Sometimes a single symptom — especially a general one, such as fever or pain — can be a sign of any of many different types of injury or disease.

tissue     Made of cells, any of the distinct types of materials that make up animals, plants or fungi. Cells within a tissue work as a unit to perform a particular function in living organisms. Different organs of the human body, for instance, often are made from many different types of tissues.


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