Increase in threshold level on applying subthreshold, slowly rising stimulus is known as
Accommodation- Slow rising subthreshold stimulus failing to produce action potential even when the normal threshold levels are reached. This occurs because of inactivation of voltage-gated Na+ channels. 
Adaptation- Persistent application of suprathreshold stimulus fails to generate repetitive firing.
Refractoriness- A stimulus to the nerve does not elicit a response.
Electrotonus- When a current is passed through electrodes kept on the surface of a nerve, current passes through it resulting in a change in membrane potential and development of electrotonic potential.
Adaptation
Accomodation
Refractoriness
Electrotonus