Monosynaptic Reflex: When an arc reflex has only 2 neurons – 1 sensory neuron and 1 motor – it is referred to as a reflex that is monosynaptic. This designates the existence of only a single synapse of chemical. In cases of reflexes of the peripheral muscle such as Achilles reflex or patellar reflex, brief stimulus to the muscle rod results in a contraction of the effector or agonist muscles.

In contrast the polysynaptic reflex pathways have one or more interneurons connecting sensory or afferent and motor or efferent signals. All reflexes except for the simplest are polysynaptic, permitting inhibition or processing of reflexes of polysynaptic within the spinal cord.