Nerve fibres. Coloured scanning electron micrograph SEM of nerve fibres brown. A group of nerves such as this is known as a fasciculus. The fibres are held together by connective tissue in the form of strands of collagen red. Each nerve fibre consists of a nerve cell axon, the output process of a nerve cell, covered in an insulating fatty layer known as a myelin sheath. Myelin isolates the nerve from its surroundings, increasing the speed of nerve transmissions. Nerves collect, interpret and relay information. The fibres are used to pass the information on to other parts of the body, such as the muscles and organs like the brain.