Final answer:
The neural impulse travels faster when the axon is encased by a myelin sheath due to its insulating properties and the nodes of Ranvier that facilitate saltatory conduction.
Step-by-step explanation:
The speed at which a neural impulse travels is increased when the axon is encased by a myelin sheath. The myelin sheath acts similarly to insulation on an electrical wire, preserving the electrical impulse as it travels along the axon. This occurs because the myelin sheath prevents the electrical signal from dissipating, allowing the impulse to travel faster and more efficiently.
Moreover, specific gaps in the myelin sheath, known as nodes of Ranvier, allow the nerve impulse to be rapidly transmitted down the axon by enabling the signal to 'jump' from node to node in a process called saltatory conduction. This efficient transfer of electrical signals results in faster communication between neurons and other cells.