CBD Oil and pain: 3 - how do we feel pain

Pain has a huge impact on society and a lot of people are looking for ways to manage their pain. At Peach & Moon Organics one of the most common questions asked by people around South Africa is 'will CBD help manage my pain?'. 

This is part 3 of a series of blog posts relating to CBD and pain. Part 1 covers the different types of pain and you can read more by clicking here. Our second blog covers the impact of acute and chronic pain, and you can read more about that by clicking here. 

This blog post covers some basics on the physiology of pain to lay the foundation for understanding how cannabis and specifically CBD can help to reduce pain. We will look at three different types of pain: pain felt at the time of an injury, inflammatory pain and neuropathic pain.

Pain involves the nervous system. The nervous system can be thought of as the bodies electrical wiring. There are two parts to the nervous system:

1. The central nervous system - spinal chord, brain and brain stem 

2. The peripheral nervous system - nerves that branch out from the brain and spinal chord extending to the other parts of the body

 Let's look at an example for the first type of pain - pain felt at the time of an injury. Suppose you stab yourself in the hand with a needle - how do we feel this sensation as pain? The surface of our bodies are covered with peripheral nerves and the end of these nerves are in our skin. Some of these endings are sensitive to pain, while others are sensitive to things like temperature or touch. Those that are sensitive to pain (pain sensors) are called nociceptors and they have a high threshold for activation, so that only something intense will produce the pain signal. Pain sensors are activated by a physiological process called transduction. A needle stabbing your finger would activate the pain sensor as would other factors that have the potential to cause tissue damage. Transduction is what causes the pain signal ('sciency term for the pain signal is action potential).  The pain signal or action potential travels along the peripheral nerve to the spinal cord. The information can then travel along the spinal cord to the brain stem and to different parts of the brain and we then perceive the experience of pain. 

A really great video which offers a fantastic explanation about how this all works in more detail can be watched by clicking here. We can see more detail about conduction along the peripheral and central nervous system. 

Now the question becomes, how do we use medicine to help with this type of pain? We use nerve block for acute pain to interfere with pain signalling. In other words nerve block interferes with conduction along the periphery to the central nervous system.  For example the dentist will use a nerve block injection. 

Let's very briefly explore the transmission of pain signals to where it is perceived as pain in the brain.  Where the peripheral and nervous system meet we find the synapse (this is in our spinal cord). The nervous system consists of millions of synapses. Essentially the synapse is the meeting point between two neighbouring neurons (nerve cells). Think about the end of a peripheral neuron transmitting a pain signal to the beginning of a second central neuron - the area between these two neurons is called the synaptic gap. The peripheral neuron contains neurotransmitters, while the central neuron has tiny receptors. When there is a pain signal from the periphery nervous system the neurotransmitters are spilled into the synaptic gap and cross over it, binding to the receptors on the other side. This leads to a pain signal (as we mentioned earlier the term would be an action potential) which is transmitted to multiple places in the brain. These sites are involved in different mechanisms. For example, some areas of the brain are involved in motor response to pain, others in pain sensations (do we experience pain as sharp/dull/burning) and other sites are involved in the emotional response to pain (for example anxiety). All of the processes involved in recognising pain are referred to as pain perception.

The identification of many of the neurotransmitters and receptors (and how they function) has led to the development of many pain medications. Cannabis can also bind to some of our receptors. We will explore this further in another blog post.

 Earlier, we used the example of  stabbing yourself in the hand with a needle (this is considered acute exposure to a noxious stimuli). If this goes on for a long time or is very intense then there may be tissue damage. The body responds to tissue damage with inflammation (inflammation is painful). Inflammatory pain is the second type of pain we will discuss. 

We spoke about inflammatory pain in blog post 1. When there is damaged tissue substances spill out of injured cells. Here is what happens:

1: Nociceptors get irritated causing pain.

2: These substances attract inflammatory cells that release substances for repair of damaged tissue but they also irritate nociceptors.

We can see that after an injury and acute pain we can get a new pain called inflammatory pain and neurons are sensitised. The transduction process is ongoing. The pain will continue until the inflammation is resolved. Another thing that happens is called hyperalgesia - usually the threshold for activating nociceptors is very high but hyperalgesia means that this threshold drops so if we touch the inflamed area the perceived pain is much stronger and disproportionate to the pressure or force of the touch. 

 Then we have a third type of pain called neuropathic pain. In this type of pain the transduction process no longer exists. In this case what has happened is that a disease or injury activates the pain system through something called ectopic pain signals. The signal travels along the pain pathways and causes the perception of pain in the brain. Those with neuropathic pain also report hyperalgesia (disproportional pain response to stimuli) and spontaneous ongoing pain. Allodynia is also frequently reported - we discussed this in blog 1. It is the phenomenon where pain is experienced from something that is ordinarily painless (such as something like a light wind on the skin or running water).  Allodynia and hyperalgesia stems from sensitisation of pain pathways in the central and periphery nervous system. 

We have now covered the physiology of three types of pain. Pain felt at the time of an injury activating otherwise normally functioning nociceptors, inflammatory pain from tissue damage and senstisation of nociceptors, and  neuropathic pain which is the result of damage to the pain pathways. With neuropathic pain the nerves that transfer information have been damaged and this type of pain does not get better with common medications used as pain killers (such as paracetamol and ibuprofen). Many of the medications prescribed for neuropathic pain are also used for treating other conditions such as anxiety and depression. It is important to understand the type of pain in order to treat it correctly. 

In our next blog we will look at the modulation of pain and then following that the pharmacological treatment of pain.