system
Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
The increase in the threshold of a receptor when a series of stimuli of subthreshold intensity are applied in succession is called
assistant
The correct answer is  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.