Which sequence best represents the course of an impulse over a reflex arc?

Which sequence best represents the course of an impulse over a reflex arc?

1. effector, sensory neuron, synapse, motor neuron, receptor
2. receptor, motor neuron, synapse, sensory neuron, effector
3. receptor, sensory neuron, center, interneuron, effector
4. none of the above
5. * receptor, sensory neuron, synapse,motor neuron, effector