What does the myelin sheath do?

It’s an insulating layer that is formed amongst nerves such as nerves in the brain or spiral cord and it’s made of fatty substances and protein it allows eletric impulses to be transmitted swiftly

It acts an insulator on the neurons. The neurons are covered with it and hence the nerve impulses have to jump over the myelin sheath to reach other neurons. This causes nerve impulses to move rapidly from neuron to neuron.