Your nervous system is made up of the central part, the brain and the spinal cord and the peripheral part, the progressively smaller nerves that spread from your spinal cord over and into your body like tiny rivers with many branches. 

Electrical signals flow up and down the nerves relaying information to and from the brain. There is a conscious system which controls feeling and movement and an unconscious system that controls the function of your organs like the heart, lungs, gut, kidneys sexual organs and all the rest. 

Nerves can become damaged by many disease processes, by inadequate nutrition such as Vit B12 deficiency, by direct damage such as accidents or pressure being caused by other tissues compressing nerves such as slipped discs. There is a very long list of things that can cause damage to nerves. Sometimes the damage can be reversed and sometimes not. 

The function of nerves will deteriorate if they are being damaged, and because nerves control all the important functions in your body, it is important to act to prevent damage. Some of the symptoms that may alert you that there may be damage caused to your nerves are obvious, such as having pain or prickling feelings on some part of your body or losing power in your arms and legs or the muscles of your face. Other symptoms may be less obvious, such as losing control over the rhythm of your heart, bowel, or bladder function. 

The most important thing is to be on the lookout for these symptoms and by knowing your body well. Do not wait when you become aware of any of these symptoms but approach a trusted medical professional straight away so that they may look into it. 

They will take a history and examine you and sometimes further tests such as blood tests, MRI scans or other specialist tests like electromyograms may be required. The treatment depends on the underlying cause but may be as simple as adapting your lifestyle or taking simple medication. Sometimes however more complex treatments may be required such as pain procedures or rarely, surgery.