Welcome to my first post on this blog. I decided that my opening should be something within my field of knowledge. This is to act as an introduction to both myself and what I plan to use this blog for. My aim is to make science simple and to express things in a way that anyone would understand. I see regularly that the general media can sometimes misinterpret or blow out of proportion scientific research. The term “scientists have said” is more cliche than Sean Bean dying in every movie he appears in. I wish to translate what they’re saying and why along with some information about how this could change our understanding of the world around us.
What makes me feel qualified to talk about this, to put it simply I am a scientist or at least I have experience studying it, working in a lab, attending conferences and giving talks about it. However I was always spent my time talking to other scientists. I want to reach out and communicate with people who aren’t experts in the field and hopefully have them develop an interest. I have always had a love for science. During my final year of school, I ended up attending a talk about how science has affected our day to day lives. I would highly recommend Better Looking, Better Living, Better Loving the fantastic book by the speaker John Emsley. From skin care products to the development of contact lens, the area that I found most engaging was the creation and development of drugs. This led me to undertake a degree in Pharmacology, which is not as one friend thought farm ecology and that I would be studying the breeding grounds of sheep (they ended up at Oxford so you all have a chance). After my degree I intended to pursue science further, spending four years working on a PhD focusing on understanding pain. I thought the best place to start was with a little introduction to pain and how it works.
A Painful Start
What is pain? Why is my body doing this? These are some thoughts that may go through your mind after stubbing your toe on a table leg, along with a chain of expletives. In most cases from our body’s point of view the answer is simply defence, pain is an evolutionary benefit to our survival. Warning us when we put ourselves in danger, as well as enforcing the mindset to not repeat it. Learning that it isn’t a good idea to put your hand in a beehive or directly onto a hot pan. The body reacts at an incredible speed to prevent damage from occurring hopefully managing to escape with a mere “ouch!” Providing us information as to where something is wrong is valuable, some signs of serious problems are often accompanied by pain such as appendicitis or cancer.
There does exist a small group of people, truly a minute percentage who do not experience pain at all. Some may call this a gift or a super power, but it comes at a price. Gory stories of horrific burns and broken bones without the person even noticing anything had happened. Pain as horrible as it can be is in most cases (sadly pain can go wrong) is a necessary evil to protect us.
The pain system itself is made up of three distinct regions, the site of injury, this could be damage to the skin or muscle as well as internal organs. The spinal cord which functions as the body’s information highway travelling on to the final area; the brain. All of these regions are connected by nerves the electrical circuitry of the body linking together your paper cut to the rest of the pain system.
The main pain detecting nerves are the nociceptors (noci translates to pain or injury). They have the specific purpose of recognising unpleasant inputs. They are covered in different receptors that can detect the type of pain being experienced. We have categorised pain into three main categories; mechanical (cuts and bumps), chemical (acids, bleach) and thermal (burns through heat or cold). There are specially evolved receptors that are able to distinguish between all these different sensations. There are a huge number of different types, each with a distinct purpose and accompanied by a lovely long name.There are far too many to go into, but as an example the transient receptor potential vanilloid 1 or TRPV1, the first in the family of vanilloid receptors can detect changes in heat. The chefs among you may notice the similarity in name to vanilla, the vanilloids are a large family of chemicals that are able to interact with this receptor. However there is a far more infamous vanilloid that is able to turn these receptors on tricking your body or more typically your mouth into thinking it’s hot. Found in chilli peppers the chemical capsaicin sticks to these receptors turning them on producing the sensation of feeling hot. Always a good idea to wash your hands as you don’t want that capsaicin getting anywhere more uncomfortable.
If you were to cut your finger the cells that make up the layers of protective skin would break releasing their contents into the surrounding environment. The waiting nociceptors are able to detect these chemicals generating within them an electrical signal that shoots from your hand to the spinal cord. The spine functions as a junction box passing information to the brain while also relaying another set of signals back to the arm triggering muscles within the arm to pull your hand away from whatever cut you, known as the pain reflex.
Nociceptors aren’t the only factors at play they are heavily influenced by the actions of the immune system. In response to cell damage immune cells are recruited to the area. Your skin no matter how many times you wash will have bacteria on its surface. The skin is the best barrier we have to keep things that would mean us harm out. With a wound now open these bacteria will seize the opportunity to rush past the breached walls, and it is the immune system that will send forward the ground forces to deal with them. The main immune cells of the body are a family called the white blood cells making up the majority are the neutrophils. They release cytokines and other inflammatory chemicals. These function to call other cells and increase the blood flow to the area. This is what causes the swelling and redness you see around injuries. These chemicals referred to as inflammatory mediators are able to affect the function at the nociceptors. They do this by reducing the required threshold to turn them on meaning things that wouldn’t normally be painful become so. The reason for this is again defensive, by making an injured area more sensitive to pain you are more likely to protect it. This is called allodynia the sensation of non-painful inputs becoming painful.
Neutrophils and macrophages are specialised white blood cells that work to protect the body from foreign threats. Cytokines released by these cells act to signal other immune cells to come to the area like a homing beacon or alert signal. Other chemicals released also act to sensitise the injured or invaded area to potentially help in defending it from further harm. Along with this they work to basically eat up bacteria in a process called phagocytosis. The cell will basically wrap itself around the bacterial cells and consume it.
The immune cells then go to work clearing up the debris of broken cells and any bacteria that may have made their way from your skin inside. The macrophages go round eating up any foreign invaders. The site of the injury will then return to normal as new skin is made to eventually seal away the outside world and any other damaged tissues are replaced. The immune cells return to a resting state and the nociceptors lose their increased sensitivity; bringing the tissue back to a relative normal.
Most of what I’ve discussed only covers the events at the site of the injury and doesn’t even scrape the surface of the pain system. The roles of the spinal cord and the brain as well as different types of pain. We can also experience neuropathic (nerve damage), visceral (internal) and cancer related pain. I will get to discuss the role of the spinal cord and brain in a follow up post. For now it’s important to see that pain is there for our benefit providing us the knowledge of where the pain is and how intense it feels. Without it we would be walking disasters not really know what has happened to us.
Reading Sources
- Textbook of Pain, Wall & Melzack.
- Central sensitization: implications for the diagnosis and treatment of pain, Clifford Woolf.
- Cellular and molecular mechanism of pain, Basbaum AI et al.
- A capsain-receptor homologue with a high threshold for noxxious heat. Caterina MJ et al.
NociSci 