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decerebrate rigidity[dē′ser·ə‚brət ri′jid·əd·ē]
a sharp increase in the tonus of extensor muscles and a relative relaxation of the flexor muscles, arising as a result of severing the brain stem—that is, decerebration. In decerebrate rigidity the reflexes that maintain body balance and the ability to move are lost; the trunk and all the animal’s extremities are extended and stretch spasmodically and the head is thrown back (so-called opisthotonos). The cause of decerebrate rigidity is the freeing of the tonic centers of the medulla oblongata and the spinal cord from the inhibitory control of the reticular formation of the medulla oblongata and the midbrain.