Sandra was 74 years old. She often complained being fatigue, having muscle cramps, difficulty swallowing, and needing machines to help her breath. During reflex tests, she also showed absents of some reflexes. Both her presynaptic and postsynaptic neurons were low in numbers. Her postsynaptic neurons were lower than presynaptic neurons. With further investigation, it was revealed that she was exposed to a chemical that increases intracellular protein production in the nerves. This unknown chemical could also increase release of excessive excitatory neurotransmitters which could cause death in postsynaptic neurons. Knowing that rise in massive amount of Ca 2 in cytoplasm of postsynaptic neuron could kill the nerve, propose two mechanisms that may be involved in Ca2 entry to the postsynaptic neurons after the release of the neurotransmitters in the synaptic cleft: (Hint: need to show how Ca 2 enters the neurons)