. Advanced biology. Biology; Physiology; Reproduction. CONDITIONED REFLEX 217. A reflex arc is traversed when the finger touches a nail. The sense organ in the skin is stimulated, the stimulus is carried over the afferent or sensory neuron through a synapse to a motor neuron. This ends in a muscle which contracts and causes the finger to be pulled away. are motor, which result in a number of reactions. Reactions of the second level are more complex than those of the first level and will involve parts of the bodv somewhat distant from the point of stimulation. When the knee jerk arouses thought
. Advanced biology. Biology; Physiology; Reproduction. CONDITIONED REFLEX 217. A reflex arc is traversed when the finger touches a nail. The sense organ in the skin is stimulated, the stimulus is carried over the afferent or sensory neuron through a synapse to a motor neuron. This ends in a muscle which contracts and causes the finger to be pulled away. are motor, which result in a number of reactions. Reactions of the second level are more complex than those of the first level and will involve parts of the bodv somewhat distant from the point of stimulation. When the knee jerk arouses thought or delibera- tion, it is classified as a third level response. For example, if the blow is so severe that one would rub the in- jured spot or examine it deliberately, certain neural connec- tions would be made in the brain. Such consequent thoughtful activities attend the reflex so closely that they are sometimes con- sidered a part of the reflex. Such reaction is called an activity of the third level. Conditioned reflex. A baby is born with the pathways for a certain number of reflexes already established. When certain sense organs are stimulated, the impulses travel along these pathways until they reach muscles or other mechanisms, which carry on the processes essential for maintaining life; such as, sucking, digesting of food, crying, coughing, and moving. When these responses are caused by other than the original stimuli, they are said to be modified or conditioned. For example, Pavlov, a Russian physiol- ogist, observed that the secretion of saliva in a dog is a reflex act, resulting from nerve pathways established in the dog at birth. The appearance of food or the taste of food in the mouth acts as the stimulus, and the flow of saliva is the response. If the same person always feeds the dog, the saliva of the dog will, after a certain number of times, flow at the sight of that person even though no food is given. The stimulus in this case is the sight of the person, not
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