During the crossed extension reflex, when a noxious stimulus is applied to one leg, which pattern best describes the opposing limb?

During the crossed extension reflex, when a noxious stimulus is applied to one leg, which pattern best describes the opposing limb?

• A. Flexors on the stimulated side are excited, and extensors on the opposite side are inhibited
• B. Flexors on the stimulated side are inhibited and extensors on the opposite side are excited
• C. All leg extensor muscles are inhibited on both sides
• D. Flexors on the stimulated side are excited, and extensors on the opposite side are excited

Answer: (A)

Crossed extension reflex involves a protective pattern where withdrawing the stimulated leg is paired with extending the opposite leg to maintain balance. When a noxious stimulus hits one leg, the leg that’s stimulated responds with flexor activation to withdraw, while interneurons cross to the other side and activate the extensors there to support the body. In other words, the opposing limb shows increased extensor muscle activity to bear weight, and the flexors on that limb are dampened to allow full extension. This contrast between withdrawal on the stimulated side and extension on the opposite side is what preserves posture during a painful input.

Crossed extension reflex involves a protective pattern where withdrawing the stimulated leg is paired with extending the opposite leg to maintain balance. When a noxious stimulus hits one leg, the leg that’s stimulated responds with flexor activation to withdraw, while interneurons cross to the other side and activate the extensors there to support the body. In other words, the opposing limb shows increased extensor muscle activity to bear weight, and the flexors on that limb are dampened to allow full extension. This contrast between withdrawal on the stimulated side and extension on the opposite side is what preserves posture during a painful input.