Acclimatisation is the process by which the nervous system fails to respond to a stimulus, as a result of the repeated stimulation of a transmission across a synapse. Acclimatisation is believed to occur when the synaptic knob of the presynaptic neurone runs out of vesicles containing neurotransmitters due to overuse over a short period of time. A synapse that has undergone acclimatisation is said to be fatigued.
Acclimatisation is said to be responsible for 'getting used to' background noises and smells.
References
Acclimatisation (neurones) Wikipedia(Text) CC BY-SA