Monosynaptic Vs. Polysynaptic
When a reflex arc consists of only two neurons in an animal (one sensory neuron, and one motor neuron), it is defined as monosynaptic. Monosynaptic refers to the presence of a single chemical synapse. In the case of peripheral muscle reflexes (patellar reflex, achilles reflex), brief stimulation to the muscle spindle results in contraction of the agonist or effector muscle. By contrast, in polysynaptic reflex pathways, one or more interneurons connect afferent (sensory) and efferent (motor) signals. All but the most simple reflexes are polysynaptic, allowing processing or inhibition of polysynaptic reflexes within the spinal cord.
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