Nerve cells are also called neurons. They are adapted to carry electrical impulses from one place to another. They feature:
The axon is insulated by a fatty (myelin) sheath. The fatty sheath increases the speed of the nerve impulses along the neuron.
Myelination is the process of myelin developing around the axon fibres. It continues from birth to adolescence.
Certain diseases, such as multiple sclerosis and poliomyelitis, cause the myelin sheath to be destroyed. This causes damage to motor neurons which means that muscles no longer receive signals from the brain or spinal cord. This results in loss of strength and co-ordination in the limbs.
Myelin sheath is produced by glial cells. Glial cells do not transmit nerve impulses. Instead they maintain homeostasis, form myelin, and provide support and protection for neurons. Glial cells also remove any debris by phagocytosis.