Answer: fibrillated

AnswerCrossword Clue
fibrillated(of a fiber) Split up into fibrils
fibrillatedFIBRILLATE, to undergo fibrillation
fibrillatedBreak (a fiber) into fibrils
fibrillated(of a muscle, esp. in the heart) Make a quivering movement due to uncoordinated contraction of the individual fibrils