Explain, physiologically, how you would decide to use ice or heat on an injury?

Question

My book doesn't have any good info on this question. Is there a reputable website or article to get info to answer this question?

Answer 1

http://orthopedics.about.com/cs/sportsmedicine/a/iceorheat.htm

http://health.howstuffworks.com/medicine/first-aid/ice-or-heat-for-injury.htm