Nerve impulses carry electrical signals between sense organs, the central nervous system and effectors to coordinate fast responses.
Neurones transmit nerve impulses.
The diagram shows a neurone.
Some neurones do not have a myelin sheath.
A scientist investigates the impulse speed for neurones with different diameters. She does this for neurones with a myelin sheath and neurones without a myelin sheath.
The graph shows the scientist's results.
Impulse speed in m per s
Which conclusion is supported by the graph?
impulses are always faster in neurones with a myelin sheath
neurones always have a myelin sheath
wider neurones have a myelin sheath
wider neurones have faster impulses