Nervous system

it is the nerve pathway involved in a reflex action, including at its simplest a sensory nerve and a motor nerve with a synapse between

• arrival of stimulus and activation of receptor
• activation of sensory neuron
• info processing in the CNS
• activation of motor neurons 
• response of preipheral effectors

by way of dorsal root

• monosynaptic
• polysynaptic

• strech reflex
• no interneuron, sensory neuron in spinal cord
• fast response 
• e.g patellar reflex

• produce more complex responses
• interneurons can control motor neurons in several muscle groups simultaneously