Motor end plates are associated with

Motor end plates are associated with muscular contractions. Motor end plates are the large and complex end formation of a motor neuron that builds contact with the skeletal muscle fibers. Without motor end plates, muscular contractions will not be possible. This works highly during emergency situations where the body takes a fight or flight reaction. 

A good example is when the fingers touch a burning candle; these motor end plates get quick impulses from the brain and send signals to the muscles to move it away to prevent further damage to the body. Without motor end plates we would be in a heap of trouble as this is the mechanism of the body responsible for motor skills and quick reaction time.

C. gemstones they are the only non metallic mineral from the list.