When a reflex arc consists of only two neurons, one sensory neuron, and one motor neuron, it is defined as monosynaptic. Monosynaptic refers to the presence of a single chemical synapse. ... By contrast, in polysynaptic reflex arcs, one or more interneurons connect afferent (sensory) and efferent (motor) signals.

Why do we need Polysynaptic reflexes?

A polysynaptic pathway also mediates the effects of flexor-reflex afferent (FRA) fibers. ... To achieve appropriate gain control of postural reflexes, information is needed that signals the influence of gravity on the body. This information is insufficiently provided by muscle stretch receptors and the vestibular system.

Why do Monosynaptic reflexes exist?

In a monosynaptic reflex, the message travels from the sensory neuron to the motor neuron with only one synapse. ... In the spinal cord, the signal crosses a synapse to a motor neuron and then travels back to the same muscle. This muscle contracts and causes the leg to kick forward.