Understanding Pain, A Ten Week Ecourse: Part 5
By Jonathan Blood Smyth
Week 5 - The Structure of the Pain System, Part 2
This is Jonathan Blood Smyth, Founder of The Physiotherapy Site and author of Secrets of Pacing, and welcome to the fifth instalment of my Ten Week Ecourse, I hope you find it interesting and stimulating.
Part Five continues the anatomy of the pain producing system, the way that pain is perceived by the tissues and conveyed up through the central nervous system to the brain. This part covers how it gets through the spinal cord and up towards the brain where we feel it.
You are welcome to publish this course in your newsletters of on your web site, on condition you do not alter it and that you keep the resource box at the bottom of each instalment.
Last time we talked about the the way the pain travels up the peripheral nerves and connects with the various layers of cells in the spinal cord. There are patterns of typical connections, which can become disturbed and abnormal in pain syndromes.
Spinal Cord Transmission Pathways
Signals travelling up towards the brain take two major pathways, the anterolateral (front and side) system and the dorsal (back) column system. The anterolateral system carries signals mostly about pain and temperature but also some touch.
The dorsal system carries touch and proprioceptive (joint position sense) information. Joint position sense, the ability to know where your body is without thinking about it or looking, is very important in our ability to maintain postures and move successfully.
The thalamus is the last link in the chain of connections which leads up to the sensory cortex, that area of the complex brain where we feel pain. It collects and processes most incoming information before transferring up to the cortex.
There is a thalamus on both sides, small masses of nerve cells acting as transmission stations on the pain pathways.
As the pain pathways continues, it goes through a series of different structures on its way up to the cortex. These structures control many aspects of our behaviour, such as fear and anxiety, vocalisation (crying out from pain), control of circulation, arousal (getting ready to act), control of breathing and heart function, modification of pain, aversive behaviours (avoiding pain), emotional expression of pain, increased adrenaline, increased blood supply to muscles, memory and movement.
This complex of multiple connections along the nerve pathways influences all the aspects of the individual which pain influences. We need to respond to pain in so many ways, emotionally, searching for answers, taking actions, getting help and avoiding painful activities.
Reaching the cerebral cortex
To make an impact on us, impulses have to get up to the feeling area in the most complex, most evolved brain areas, the cerebral cortex. If pain impulses don’t get up to the cortex, we don’t have a pain. If pain impulses appear in the cortex but are not caused by any disease process, we do have a pain.
From the thalamus, the nerve pathways proceed towards their final target, the somatosensory (body-feeling) areas of the cerebral cortex. The areas of nerve cells serving different areas of the body depends on the importance of those areas. The thumb, hand, face and lips have very large areas devoted to them, indicating their importance in our lives.
Pain impulses are not confined to the areas which feel pain but are sent to all sorts of nearby areas in the brain. This reflects the complicated nature of pain, with its need to feel where a pain is, reflect mood changes associated with pain, and allow changes in the automatic and muscle control body systems.
From the cortex down
No, the messages don’t always go up to the cortex for interpretation. The cortex has huge influence on lower areas of the nervous system, affecting the type and intensity of incoming impulses. These downgoing nerve pathways are called corticospinal projections and are more influential and numerous than usually recognised.
The exact role of the corticospinal projections has not been well researched, but downgoing impulses along these nerves can both inhibit or excite spinal cord cells further down. This can change the nature of messages coming up to the brain, either reducing their strength or increasing it. This is another method by which pain can be altered before it gets up to its eventual destination in the cortex.
The cortex has the power to influence its own inputs, to at least partly decide what information and at what strength comes up to itself. It can decide how urgent it is for this information to reach conscious levels, at what intensity and at what time.
Lessons from the anatomy of the nervous system
Research into the nervous system has revealed several interesting aspects in the way it feels, processes and deals with pain.
- Pain is not felt via just simple pain receptors, but felt in various ways through several different types of nerve.
- There is no single pain pathway up to the brain. Pain can travel in various routes and connects in varying areas in the spinal cord.
- Pain can be influenced by many incoming impulses at many places in the pathway to the brain.
- When the pain gets up to the brain, there isn’t a pain area. Pain is perceived using many areas of the brain and this may be due to its complex nature.
- The brain can determine its own incoming pain levels to some extent by influencing the nerves lower down to send more or less pain up towards our conscious minds.
- Even though very complex, an understanding of this system can lead to insights in how to manage pain in real people.
Check out the sixth instalment of the Pain Ecourse.
Understanding Pain, A Ten+ Week Ecourse by Jonathan Blood Smyth.
The Physiotherapy Site is your resource for orthopaedics, joint replacement, physiotherapy and pain.