Which of the following occurs at a neuromuscular junction? 1. Acetylcholine is released from a motor neuron then binds to receptor sites on a muscle cell 2. Troponin binds to myosin 3. Calcium is released from the nerve terminal of a motor neuron 4. A nerve impulse travels from a motor neuron to a muscle cell initiating the events of contraction 5. Both statements 1 and 4 are correct