Reflex arc

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A reflex arc is the neural pathway that mediates a reflex. It generally does not involve the brain. In higher animals it is composed of a spinal "reflex integration center" composed of interneurons to connect affector (sensory stimulation) and effector (response) signals. While the reflex generation may be initiated by nociceptive input, extensive processing takes place within the spinal cord. The neural connection from the primary sensory neurons to the motor neurons is a poly-synaptic pathway (Andersen).

In lower animals reflex interneurons not necessarily inolve the spinal cord, see e.g., lateral giant neuron of crayfish.

A reflex to a stimulus is almost simultaneous, as the reflex arc doesn't involve the brain at all.

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