Physical Therapy Assistant Practice Exam

Which reflex is integrated by 1-2 months of age and is stimulated by a noxious stimulus to the foot?

1. Crossed extension reflex

2. Osteoblast reflex

3. D2 flexion pattern

4. Tonic labyrinthine reflex

The correct answer is: Crossed extension reflex

The crossed extension reflex is a protective reflex that develops early in life, typically integrating by 1-2 months after birth. It is initiated when a noxious stimulus, such as a painful stimulus to the foot, causes the flexion of the stimulated leg and simultaneous extension of the opposite leg. This reflex plays an important role in maintaining balance and posture, as well as aiding in protective mechanisms by promoting withdrawal from harmful stimuli. In infant development, the integration of this reflex is crucial as it indicates a normal progression of neurological function. When the foot experiences a noxious stimulus, the immediate reaction is flexion of that leg to withdraw from the source of pain, while the opposite leg extends to help stabilize the body and prepare for potential movement or reaction to the stimulus. The other options do not relate to the noxious stimulus to the foot or do not integrate by the specified age. The osteoblast reflex is not recognized in neurodevelopmental terms, while the D2 flexion pattern and tonic labyrinthine reflex do not respond specifically to noxious stimuli nor typically integrate within this early timeframe. This highlights the significance of the crossed extension reflex in both protection and motor development during infancy.