Which description matches the asymmetrical tonic neck reflex?

• A. When turning the head to one side, both arms extend
• B. When turning the head to one side, the ipsilateral arm extends and the contralateral arm flexes
• C. When the cheek is stroked, the infant turns toward the stimulus
• D. When startled, the arms abduct and the fingers spread

Answer: (B)

The main idea is the asymmetrical tonic neck reflex, a primitive reflex where turning the head to one side produces an asymmetric pattern in the limbs. When the head is turned to one side, the arm and leg on that same side (ipsilateral) extend, while the opposite arm and leg (contralateral) flex. This creates the classic fencing posture: head turned, same-side arm and leg straight, opposite-side arm and leg bent. It’s typically integrated by about 4–6 months of age; if it persists beyond infancy, it can interfere with activities like feeding, rolling, and hand-eye coordination because the abnormal posture disrupts coordinated movement. The other described responses don’t match this pattern: bilateral extension occurs with other reflexes or states, rooting involves turning the head toward stroking of the cheek, and the Moro reflex involves sudden abduction with arm and finger spread.