Illustration of a section through a nerve cell (cell body at top centre) showing its myelinated axon. The axon is the nerve fibre that passes information to other nerve cells, or to effector cells such as muscle fibres. Myelin is an insulating fatty layer that surrounds the nerve fibre, increasing the speed at which nerve impulses travel. It is formed when Schwann cells wrap around the fibre, depositing layers of myelin between each coil. The outermost layer consists of the Schwann cell's cytoplasm and is known as the neurolemma or sheath of Schwann.