Concussions, head shots, cheap blows. There's been a lot of talk in pro sports lately of doing something to cut down on the number of injuries that occur in games played by very large, very strong and very talented athletes - especially in hockey and football.

Toronto Blue Jays' John McDonald collides with Minnesota's Justin Morneau at second base in a play that gave the Twins' star a concussion. He will be out at least another week. (Chris Young/Canadian Press)Yet, in 2010, two of the highest profile athletes to miss significant chunks of the season were Canadians in a mostly-American game: baseball: Jason Bay of the New York Mets and Justin Morneau of the Minnesota Twins.

Bay missed the last two months of the season after his head bashed into the left-field wall while he made a running catch at Dodger Stadium in Los Angeles in late July. Two weeks earlier, Morneau slid hard into second base during a game in Toronto, colliding with the shortstop.

Both players made what are considered good plays: Bay was able to hang on to the ball for the final out of the inning and Morneau's hard slide impeded Toronto's shortstop in his effort to throw out the runner going to first base. And in both incidents, the players - while apparently momentarily dazed - were able to get to their feet and walk off the field. "Always a good sign," as the announcer says at the end of the video of Morneau's incident posted on the official site of Major League Baseball.

Both players were out for the rest of the season because of ongoing symptoms of concussion.

What is a concussion?

A concussion is an injury to the brain resulting from a blow to the head. Your brain is protected from everyday bumps and jolts by the cerebrospinal fluid that it floats in, inside your skull. A hard enough jolt, though, causes your brain to smack into your skull.

Most people don't black out when they suffer a concussion. In fact, they may feel little more than a bit dazed at first and - like Jason Bay and Justin Morneau - be able to get up and walk away with little sign of injury.

A concussion is the mildest form of traumatic brain injury. In medical parlance, traumatic is used to indicate "sudden" as opposed to "chronic" which develops over a long period of time.

What are the symptoms of concussion?

Classic concussion symptoms include confusion and amnesia, especially of the event that caused the concussion.

Other immediate symptoms may include:

• Headache.
• Dizziness.
• Ringing in the ears.
• Nausea or vomiting.
• Slurred speech.
• Fatigue.

Other symptoms may show up in the days and weeks following the incident. They include:

• Memory or concentration problems.
• Sensitivity to light and noise.
• Sleep disturbances.
• Irritability.
• Depression.

Like any head injury, it is important to watch the patient closely for 24 hours. If the patient loses consciousness often or has trouble waking up, you should seek immediate medical attention.

What should I look for if I suspect my child has suffered a concussion?

Kids can be particularly at risk for concussion - even if they're not involved in sports. Falling off a couch or bumping into a table could provide enough of a blow to cause a concussion. Watch for:

• Listlessness, easy to tire.
• Irritability, crankiness.
• A change in eating or sleeping patterns.
• A lack of interest in favourite toys.
• A loss of balance or unsteady walking.

You should seek medical attention if your child loses consciousness, suffers a seizure, vomits repeatedly, has a headache that keeps getting worse, or has lasting or recurrent dizziness.

What is post-concussion syndrome?

It's when a combination of concussion symptoms persist for weeks or months after the injury that caused the concussion. They can persist for a year or more in some people.

It's unclear why the symptoms persist. Some experts believe the event that caused the concussion does structural damage to the brain or disrupts neurotransmitter systems. Others believe the syndrome is related to psychological factors, especially since the most common symptoms - including headache, dizziness and sleep difficulties - are similar to those of people suffering from depression.

When is it safe to resume activity after a concussion?

Definitely not on the same day the concussion is suffered. Beyond that, it depends.

The Second International Symposium on Sport Concussion, held in Prague in 2004, led to the creation of the Sport Concussion Assessment Tool (SCAT2). It's a standardized tool that medical professionals can use to diagnose athletes - and athlete can use to help determine if they're suffering from a concussion and whether they're ready to resume activity.

SCAT2 includes six steps to take before an athlete should return to play, with at least 24 hours for each stage. However, if symptoms recur, the athlete should return to the first stage. The New York Mets report that Jason Bay has been symptom-free since December, when he resumed working out. He's expected to be at full strength when the baseball season opens in April.

As for Justin Morneau? The Minnesota Twins say he continues to make good progress and has been hitting, fielding and throwing. But they won't know whether he's over his post-concussion issues until he starts playing in games during training camp later this month.