How do we move, make decisions, smell, feel pain and make memories? The answer lies in our nerves, which make up the nervous system. The nervous system controls how we function and react to our environment. It has two parts: the central nervous system (CNS) which consists of sensory nerves that monitor our internal and external conditions by sending signals to our brain for further processing and action; and the peripheral nervous system (PNS) which consists of motor nerves that send signals from our brain to our muscles and organs, helping us to function and move within our environment.
Each nerve cell is divided into segments called neurons which are surrounded by a sheath. The sheath acts as an insulator and conductor speeding up the movement of the signal (action potential). As the signal moves from one neuron to another it changes from an electrical impulse to a chemical and then back to electrical impulse and can move at speeds of up to 120 metres per second.
When the system is at its optimum it works silently in the background and we are not even aware of it. But it is a delicate system and when things go wrong we cannot help but notice. So, what happens when things do go wrong? Nerves are delicate and can be damaged because of an injury (external), virus, disease or conditions. In the past we have discussed damage to the nerves of the CNS resulting in conditions such as Parkinson’s, ALS, MS and stroke but now we are going to discuss damage to the PNS caused by external injuries. Peripheral nerve injuries can be classified into three groups:
• Nerves can be injured by being overstretched and even though nerves are elastic and strong force can cause a complete tear resulting in a total loss of the signal and paralysis
• They can also be injured through a laceration and although it may cause transection most often there is some continuity.
• The third type of injury is a compression injury (pinched nerve) where pressure causes damage but there is no tear. A common compression injury is known as Saturday Night palsy, caused by resting the arm over a chair and falling asleep, putting pressure on the radial nerve leading to loss of movement and sensation. Depending on the duration of the compression the symptoms may be temporary with movement and sensation returning after time but in some cases the symptoms may be permanent.
Nerve damage may lead to neuritis—inflammation of the nerve that can be caused by an external injury or secondary to infection or an underlying condition such as alcoholism, cancer, vitamin B12 deficiency, vitamin B6 excess, diabetes, hypothyroidism or radiation therapy. Nerve damage can affect one or both sides of the body resulting in weakness, numbness and burning pain. Signs and symptoms can vary depending on the cause and area of symptoms. The most common signs are:
• Numbness or tingling in the arms or legs that can radiate into the hands and feet
• Burning, throbbing or sharp pain in a limb
• Chronic burning pain and hypersensitivity (causalgia pain)
• Heightened or lowered sensation to heat, cold and touch
• Poor co-ordination and difficulty with fine motor skills like doing up buttons and picking up small objects
• Muscle weakness and in some cases paralysis
• A tumour growing around the nerve (neuromatous)
Treatment not only focuses on the cause but also on pain and function. Not all nerve injuries will recover, especially where the symptoms are caused by a degenerative disease or condition or complete damage to the nerve. Whether the symptoms are temporary or permanent, pain may be an issue and in many cases pain medication may be prescribed but physiotherapy can also help. A physiotherapist will use a range of modalities to help relieve pain, such as massage, acupuncture and electrotherapy. Muscle weakness is also a symptom that needs attention to prevent further damage to the nerve, the muscle and the joints. Where there is no movement at all then safe handling techniques will be taught and in cases where there is some movement then exercises will be given to strengthen the muscles. It is also important to move the limbs through their normal range of movement to prevent stiffness and shortening of the muscles.
In cases where there is a chance of recovery, for example after a laceration or even a stroke, then exercise alone may not be enough to improve function. Relearning tasks and skills through sensory feedback (touch, sight and sound) is important as is performing tasks through normal movement patterns. So, remember whatever you are doing there are thousands of impulses moving through your body to make even the simplest of actions possible.
