The Nervous System

How the nervous system works?

We have receptors all over our skin. These are nerve endings or danger sensors. Different receptors pick up different information. Some react to temperature; some to pressure. The information that the receptors pick up is sent through the nerves to the spinal cord. The message that is sent is more like a question asking “do I need to protect this?” Not all messages are sent.

We are not aware of every time we are touched. We do not constantly feel our clothes on our skin and sometimes we cannot remember getting the bruise that we discover on our leg. The spinal cord acts like a postal sorting office and decides when and which danger messages are sent to the brain. When enough danger messages reach the spinal cord, the message is sent to the brain.

The brain processes the danger messages and decides if the body is at risk of harm or injury. If the brain decides the body is at risk, we will feel pain and react to get ourselves out of danger. If our hand touches something hot, the danger sensors will send messages to the brain. Our tissues are not designed to withstand much heat, so to protect the hand tissues our brain sends a response of pain and we very quickly remove our hand from the source of heat.

It is sometimes easier to think of how the danger sensors and the brain combine together to form an alarm system. As we mentioned above about the six-inch nail and the paper cut, pain does not always equal harm. Therefore, when we talk about the nerves sending messages, we like to call them danger messages. It is the brain’s use of this information from the alarm system that results in the feeling of pain. The brain is working out “do I need to protect this?”

Why does it hurt?

Most of us will have sprained an ankle at some time in our lives. Remember how quickly after the injury the area became swollen, red and tender to touch? This is because all the chemicals involved in healing arrive at the injury site to do their job and start the healing process. These chemicals irritate the nerves, making the area tender to touch. This reaction has a protective role. The first few days after the sprained ankle you may have rested more or even used crutches to ease the pain when walking which allows the injured tissues time to heal. This type of pain is called acute pain.

Over time, as healing takes place, we can walk easier and, after more time, are able to return to our normal activities. There was a useful reason for this pain. It meant we rested the injury and allowed the tissues time to heal. As the healing takes place, the chemicals stop being produced and the pain should gradually reduce and stop. 

This process takes time but the tissues will heal. A broken bone or tendon and ligament injuries will heal within six to 12 weeks. The body will continue to remodel scar tissue for three to six months after healing. 

Why does the pain last after the tissue has healed?

Researchers have learnt more about pain in the past 10 years than in the past 100 years. They can see what changes happen in the nervous system producing persistent pain; even though the tissues are completely healed. For some people the pain starts without damage to the tissues. Unfortunately, we do not fully understand why this persistent pain starts.

What is happening in the tissue to cause pain?

This type of pain is called chronic or persistent pain. In persistent pain the brain continues to receive the danger message; it thinks that the tissues may require protecting. The brain decides the body needs all the protection it can get. It starts to adapt and build more defences; it upgrades the alarm system. It needs more information from the tissues, so it creates more danger sensors. The brain thinks, the more information the better!

More danger sensors create more danger signals. All these messages are sent to the spinal cord. The spinal cord or postal sorting office becomes overloaded with messages and starts working overtime to deal with all the extra messages. It becomes quicker at processing the messages and sends out more deliveries, allowing more of the messages to be sent out as soon as they arrive. Before it would have been more selective of which messages needed to be sent. The spinal cord is now starting to amplify the signals it receives from the tissues.

Our brain receives more messages, it becomes better and quicker at recognising the danger messages. The alarm system stays on high alert. This now means that we receive the pain message more often. Levels of pressure and movement that didn’t previously hurt, can now feel painful and things that previously hurt, now hurt even more. The alarm system is now going off, for example, when someone taps the window, instead of only when the window breaks.

As time goes on

The pain starts, it does not go, and you become worried. In the past when you had pain you rested, so now you do the same and avoid movement to protect the area and avoid any potential damage.

The pain stays; you keep the reduced level of activity because any time you try to do more or do something differently, it hurts. Your muscles and tissues become weaker and less flexible as they get used to doing less. When you walk further than normal you may become out of breath and hot. You find that you can no longer do things that you used to find easy. When you become active it takes less to stress your muscles and tissues. When the tissues are stressed they release danger chemicals as the brain is now on alert and quicker at recognising these signals and is more likely to send a pain message.

When tighter tissues, weaker muscles and lots of danger chemicals irritate the over excited alarm system it is not surprising that the smallest stretch starts to feel so painful. Even though the tissues are healed as best they can, you feel pain. This pain can often feel exactly like the pain you had when you initially had your injury. This familiar pain helps to reinforce the thoughts you may be having that there must be something wrong; there must be damage to the tissues. Hopefully, by reading and understanding what has been written so far we know that this is not always true and pain does not always mean harm.

Pain and your memory

Pain memory can be very powerful. Even a memory of a specific situation that caused harm from the past, can elicit the danger alarm system to produce pain and make us act in ways that we think will protect us from further harm; even if there is no real danger the second time round.

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