What is the advantage of a polysynaptic reflex arc vs a monosynaptic reflex arc?

Answer 1

The polysynaptic reflex arc is the sudden movement to protect life and lymb. An example usually given is walking in a shallow pond and stepping on a sharpt object: the foot immeidately raises before you are voluntarily aware of pending danger. It is more complex than the monosynaptic relex and include prolonged output from the spinal cord (as opposed to one sudden stretch reflex stimulus) and decision making processes ("am I in danger?" "am I hurt?").

Answer 2

Because in a mono-synaptic reflex, only enough neurotransmitter is required to cause one post-synaptic cell to become stimulated above its threshold potential (and therefore depolarize if it is not in its refractory period). In a poly-synaptic reflex, enough neurotransmitter is required to stimulate multiple post-synaptic cells above their threshold potential. This will inevitably take longer, given the same amount of neurotransmitter release from the pre-synaptic cell.