- Spinal cord
- Dorsal root of nerve
- Dorsal root ganglion
- Ventral root of nerve
- Nerve – periferal
- Outside of spinal disc
- Inside of spinal disc
- Vertebra – the bony part of the spine.
In the previous pain blog I wrote about the immediate aftermath of a pain incident, a wasp sting or a hippopotamus getting too close to our feet. The sensation of pain goes up a periferal nerve, up the spinal column and into the brain where the magnitude of the pain, the danger we are in from all aspects of our life, plus the memories of any such similar happenings are taken into account and we then react accordingly. Pain is a very complicated, emotional process. This blog looks at an important relay station at the top of the nerve, just before it enters the spinal cord, a little bulge in the nerve called the dorsal root ganglion or, sometimes, a spinal ganglion. This little bulge relays sensory information about the world to the brain and it responds to messages from the brain about pain and stress by increasing sensitivity. If compressed, it may or may not cause pain. The dorsal root ganglion itself can cause pain. Yes, kneeling on a drawing pin hurts, but pain can come from within. 1
But before getting stuck into the dorsal root ganglion, the above diagram needs a little explanation. The spinal cord (1) is also known as the central nervous system, the information highway from body to brain and back. As can be seen, the nerves coming from the body split into 2 just before joining the spinal cord and the dorsal root part (2) carries the sensory information about the world and the ventral root part (4) carries the messages to tell muscles to contract. They join together to form a periferal nerve. In fact the diagram demonstrates a disc bulge, which will be covered in a future blog on fascinating facts about back ache. For now, the picture demonstrates how the central part of a spinal disc can protrude onto a nerve (7) and cause pain.
The wasp sting blog talked about the various sensory receptors living at the end of the periferal nerves, conveying information about temperature changes, tearing, chemicals and so on which may or may not be recognised as a danger to the body. The dorsal root ganglion nestles within the bones of the spine which should give it protection from damage. The dorsal root ganglion contains the nucleus, or control centre, of the nerve and this nucleus manufactures the various sensors and sends them down to the nerve ends. The sensors only live for a few days so need frequent replenishment- a point worth pondering on if fearful that the pain will last forever. Within the nucleus resides the DNA of the nerve, which, when activated, says which sensors to make. For instance, in order to sense movement, each joint is surrounded by a very high number of mechanoreceptors. Also, the lips, hands, feet and sex organs are surrounded by many sensory neurones.
The dorsal root ganglion is sensitive and changeable, which means it can increase or reduce levels of pain. It does this in 2 different ways, firstly as a response to changes in chemicals and secondly as a response to being squashed. The chemicals that can affect it include the stress hormones, inflammation as a result of damage to the nearby tissues and chemicals from the brain telling it to ramp up production of some of the pain sensors as a result of ongoing pain. So when we are stressed, the resultant adrenaline and cortisol in our blood sends a signal to the dorsal root ganglions to be on the alert for physical trauma and therefore potentially more sensitive to pain. This helps explain why when we feel upset or worried about something, old aches and pains seem to feel worse; its true, they do. Also when we have hurt ourselves in some way, the brain tells the DRG to make more pain sensors to discourage us from moving the injured part about and help it to heal. Another source of chemically induced response could be coming from nearby inflammation, which is thronging with immune system cells and repair cells, which can irritate the dorsal root ganglion and increase pain at the end of the affected nerves. So, whilst messing about in the snow, we decide to make a snow angel; we lie on our back and land on a shard of glass that cuts us on the back near the spine. In a couple of days, for no apparent reason we get back ache or suddenly develop sciatica; the cause is the cut is mending with the usual swelling and scabs being formed, but because of where we cut ourselves, we have also irritated a dorsal root ganglion and it is now pumping out pain receptors. A final source of chemical irritation could be a herniated (or split) disc, as in the above diagram. A herniated disc causes excruciating pain – partly because the highly acidic contents ooze around the dorsal root ganglion and send it into a frenzy of pain production.
The DRG does not like getting squashed and things that squash it include nearby inflammation, arthritic changes to the spine, or spinal misalignment. This will increase its sensitivity and it might make its own pain receptors, so it itself becomes a source of pain. However, if the squashing happens slowly over a long time, then the DRG may not get sensitised since the brain does not perceive the squashing as dangerous.
So if we suffer a major trauma, as part of the body’s defence mechanism, the control centre of the relevant nerves, the dorsal root ganglion, squirts out more pain receptors and keeps doing this until the pain subsides and we are healed. Pain hurts and causes us to fear more pain, which increases stress levels, which also has the DRG squirting out more pain receptors. The dorsal root ganglion will also respond to emotional stress and fear, which increases the possibility of us feeling pain. Pressure on the DRG from the bones or damaged tissues get it going too. So the DRG will increase pain for many reasons; however the DRG will also reduce pain when the danger or stress has gone, and it will reduce the pain within days because the pain sensors only live for a few days before dying off and needing replenishment. We just need to find the people who can help us recover physically and/or mentally. Pain is not a never ending state.
- Sources: Explain Pain, David Butler and Lorimer Moseley. Atlas of Anatomy, Thieme. Wikipedia. My notes from my R phase training with Z health. [↩]