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A reflex arc is a neural pathway that controls a reflex action. In higher animals, most sensory neurons do not pass directly into the brain, but synapse in the spinal cord. This characteristic allows reflex actions to occur relatively quickly by activating spinal motor neurons without the delay of routing signals through the brain, although the brain will receive sensory input while the reflex is carried out. Analysis of the signal takes place after action has been taken. There are two types of reflex arc: autonomic reflex arc (affecting inner organs) and somatic reflex arc (affecting muscles). It is the pathway followed by sensory nerve in carrying the sensation from receptor organ to spinal cord and then the pathway followed by motor nerve in carrying the order from spinal cord to effector organ during a reflex action. right ==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 brain. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「reflex arc」の詳細全文を読む スポンサード リンク
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