Neurons and Myelinisation

• Neurons carry the electrical impulses in the nervous system.
• Myelin is a dense, fatty substance essential for electrical impulses to travel.

Myelin sheaths begin to form during foetal development and start in the brain before progressing on to the spinal cord and the rest of the body. The sheaths electrically insulate the axon on a neuron and increase the speed of nerve connection. There are gaps between the myelin sheaths which the electrical impulses jump between. This is how the messages travel and pick up speed.

Very little myelin is present at the time of birth with the exception of the nerves involved in swallowing and sucking reflexes. Babies responses to stimuli are slow and uncoordinated at first because the process of myelinisation is still in progress.

Myelination of the nerve tracts in the central nervous system is completed by the end of the second year of life, occurring from the head down to the trunk. Parts of the limbs nearest to the trunk develop fine control before the extremities, with fine control of the digits coming later. The development of myelin sheaths in the brain takes much longer and continues right up to adolescence.

All nerves are present at birth and the growth that occurs is in size. This occurs due to their plasticity so they can be constantly remodelled. Motor control develops from head to toe and centre to periphery.