Muscle disease tends to be patchy, hence the term ‘sampling’, which is often applied to the technique of electromyographic investigation. The susceptibility of muscle pathology to electromyographic diagnosis relies on type 1 fibres being affected because motor units containing these fibres are the first to be recruited. Myelinated nerve fibres may undergo demyelination or degeneration depending upon whether the myelin or the axon is primarily affected. Severely demyelinated nerves are unstable and degenerate. Disease of nerve cell bodies cause centripetal degeneration in the longest axons, the so-called dying-back neuropathy. Severe trauma to a nerve causes distal degeneration, also known as Wallerian degeneration.