reflex

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reflex An automatic and innate response to a particular stimulus. A reflex response is extremely rapid. This is because it is mediated by a simple nervous circuit called a reflex arc, which at its simplest involves only a receptor linked to a sensory neuron, which synapses with a motor neuron (supplying the effector) in the spinal cord. Such reflexes are known as monosynaptic spinal reflexes; an example is the stretch reflex. Other spinal reflexes involve more than one synapse (see polysynaptic reflex); an example is the withdrawal reflex of the hand from a painful stimulus (such as fire). Cranial reflexes are mediated by pathways in the cranial nerves and brain; examples are the blinking and swallowing reflexes. See also conditioning.

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