Reflexes A reflex is a rapid, involuntary response to a stimulus. A reflex arc is the pathway traveled by the nerve impulses during a reflex. Most reflexes are spinal reflexes with pathways that traverse only the spinal cord. During a spinal reflex, information may be transmitted to the brain, but it is the spinal cord, not the brain, that is responsible for the integration of sensory information and a response transmitted to motor neurons. Some reflexes are cranial reflexes with pathways through cranial nerves and the brainstem. A reflex arc involves the following components, shown in Figure 1: • The receptor is the part of the neuron (usually a dendrite) that detects a stimulus. • The sensory neuron transmits the impulse to the spinal cord. • The integration center involves one synapse (monosynaptic reflex arc) or two or more synapses (polysynaptic reflex arc) in the gray matter of the spinal cord. In polysynaptic
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