So if a question asks when does the CNS initiate the reflex arc i could just answer when the receptors pick up a harmful/painful stimulus? If thats true then that means there are normal sensory receptors and pain receptors and not just one type right? I think i am overthinking this
As you suspected, there are many different receptors, temperature, pressure etc.
However, harmful/painful might be a bit too broad - we can be pained without experiencing the spinal reflex (depending on who was marking it might also be accepted but better safe than sorry).
Answers I would consider:
- when the spinal reflex is initiated (look at the question structure to see if this is too circular or not)
- when receptors detect a source of possible harm that the body must be quickly removed from to minimise damage.
- after sensory pathways have transmitted a signal from the receptors indicating a source of harm which the body should be rapidly removed from (tailored to the exact wording of your sample question)
I find it unlikely that that question would be asked