Hi. Thank you for joining our course on medical cannabis and pain. This exciting course consists of several models. Some will cover various aspects of pain, others deal with different features of the cannabis plant, whereas the rest combined the two topics and carefully observe and analyze both the positive and the negative aspects of medical cannabis when used for pain control. The first model in this course focuses on pain. By completing this model, you'll be able to differentiate between diverse types of pain, understand the role of pain as a defense mechanism, appreciate the importance of pain treatment and the consequences of untreated pain, become familiar with the basics of pain physiology necessary to understanding how medical cannabis reduces pain, and finally, recognize modern approaches to pain treatment. So, in this first lesson, let's start by asking, why do we have pain? To answer this question, we'll break pain into three different categories. First, we'll talk about acute physiological pain. Pain is one of the main defense mechanisms of the human body. We have all experienced painful episodes, such as mistakingly touching a hot iron or a sharp object like a needle. Within milliseconds, we feel pain in the affected region and even without thinking about it, we withdraw our hand away from the source of pain. So, pain alerts us to potential or actual damage to our body or to a part of it and by quickly activating their withdrawal flex, it prevents further damage to our body. So, the answer is yes. Pain in those situation is a protective defense mechanism and a very important and effective one. We'll now move to the second pain category, which is acute inflammatory pain. Our next question is, if pain remain protective defense mechanism under all circumstances? Well, here things get a little bit more complicated. Let's think about a slightly different situation. About three hours ago, you had a surgical removal of a wisdom tooth. Your dentist gave you an injection of local anesthetics a few minutes before starting the surgery, which went very well and you had no pain. A few minutes ago, you started feeling pain which has quickly worsened and is just about to become excruciating. You certainly need a pain killer as soon as possible, but what does this pain mean to the body? Does it still serve as a defense mechanism? What is it supposed to protect you from? In this case, your pain arises from inflammation around the socket of the removed wisdom tooth. The body responds to injury, trauma, surgery, et cetera by creating an inflammatory response, which is aimed to heal the damaged tissue. The response is always painful. So, you might have guessed right. In the case of the wisdom tooth removal, pain does not have a protective value. Let's pause now and take a few seconds to think about situation where you have experience a painful event, which you consider as a protective one, and another condition in which you experience non-protective painful events. Thank you for coming back. Talking about inflammation, let's give our bodies some credit. Inflammatory pain might be important. One example is a condition called acute appendicitis. The appendix is small, dead end, hollow part of the intestine. It can sometimes get inflamed for various reason. If diagnosed on time, the appendix is usually removed by a relatively simple surgical procedure and full recovery can be expected within a few days. However, if not diagnosed on time, the inflammation can cause rupture of the appendix into the abdominal cavity and lead to a catastrophe, even to death. Now, what brings a patient with acute appendicitis to a doctor is severe abdominal pain, which accompanies the inflammatory process. If pain had not been a part of the inflammation, in many patients, the outcome of acute appendicitis would have been a disaster. So, this example shows us that pain, which accompanies acute inflammation, can often be regarded as a protective mechanism as well. Another example is the following. Let's assume that you break a bone in your leg while skiing. You are on the way to a hospital in an ambulance moments after the injury. The paramedic gave you an injection of strong painkiller and you are fairly comfortable while laying quiet in the ambulance. However, a bump on the road shakes you considerably and causes an immediate extreme pain exacerbation. Again, your body responds to the injury by creating an acute inflammation around the broken bone, which, as I said before, is always painful. Any movement of the leg can potentially cause harm to the neighboring tissues, like tearing muscles, nerve, or even blood vessels. Again, pain which increases with movings serves as a defense mechanism by telling you keep still, don't move, and avoid further damage. Lastly, let's talk about this third category, that of chronic pain. So far, we have dealt with various forms of acute pain, where we saw that in many cases, pain has protective value. However, worldwide, many people, actually about 20 percent of the adult population, have another type of pain known as chronic pain. Chronic pain is pain which lasts for more than three months and has many different causes and manifestations on which we will elaborate later in this course. Nonetheless, when pain becomes chronic, one can easily understand that it loses its alarming properties and serves no more as a protective mechanism. Let me give you one example. Nerve injury or nerve damage often results in chronic pain. Elderly people are prone to have shingles. This is a painful rash which results from activation of the zoster virus. The rush typically results within one month and pain gradually subsides as well, resulting in full recovery. However, in some people, although the rash disappears, pain stays for months or even for years. These people not only experience spontaneous pain, but they also have another dreadful phenomenon. Any light touch such as a gust of wind, running water, or rubbing close against the skin results in an immediate burst of pain exacerbation. This phenomenon is called allodynia. The reason I mention this now is that this is an example of how sometimes chronic pain totally lose its protective properties because gentle touch of running water at normal temperature is never a threat to the body and should therefore never provoke no pain whatsoever. Modern pain research has taught us a lot about the mechanisms which are responsible for these dramatic changes in pain systems, especially in patients with chronic pain, but we have no clue why those changes occur.