ANATOMY

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The nerves that connect your brain and spinal cord to the muscles and skin enable movement and feeling. Once injured, the normal information flow is interrupted with a resulting loss of sensation or function and pain. If a nerve injury occurs, there is an interruption in the information being conveyed to the skin or muscles to and from the brain.

The larger nerves in your arms and legs are about the thickness of a power lead to a domestic appliance except each encloses many of thousands of microscopic nerve fibers (axons) which can be over a metre in length. For example, the sciatic nerve extends from the base of the spine to the big toe. These nerve fibres are grouped together in bundles called fascicles. Some nerves – such as the median and ulnar nerves in your arm – have motor and sensory fascicles, giving you both movement and feeling in your hand. The brachial plexus illustrates how these major and minor nerve fibres are grouped to provide the vital motor and sensory connections between the central nervous system and the upper limbs. Examples and diagrams can be seen here.

Like electrical cable, many of these nerve fibres are insulated in myelin which enables far faster transmission of impulses compared with unmyelinated fibres. In peripheral nerves, the myelin sheath also provides the framework for regrowth of the axon after injury. Human axon growth rates can reach 2 mm/day in small nerves and 5 mm/day in large nerves (in babies) but adult nerve regeneration is normally of the order of 1mm per day.