Jess is fast asleep, and her roommate crystal is studying in the next room. their cat knocks a lamp off of the bookshelf. crystal jumps up from her desk, but jess remains asleep. what brain structure is responsible for raising or lowering the threshold of conscious awareness, such that crystal reacts to the sound of the lamp falling and jess is unaware of it

It is "​the reticular formation".

It is in charge of the rest wake cycle, along these lines intervening different levels of alertness. The reticular formation has projections to the thalamus and cerebral cortex that enable it to apply some command over which sensory signs achieve the cerebrum and go to our cognizant consideration. It assumes a focal job in conditions of cognizance like alertness and sleep.  

answer; georgia,blue ridge region;

answer; heredity ;