A nurse is assessing a 3-day-old newborn. Which finding would indicate a normal primitive reflex?

This question tests your ability to differentiate between normal and abnormal newborn reflexes. The key is to identify the expected response for a specific primitive reflex in a neurologically intact 3-day-old infant. The correct answer describes the Babinski reflex, a normal finding in infants up to about 12-24 months of age due to an immature central nervous system.

Option 1 accurately describes a normal Babinski reflex. The expected response when stroking the lateral sole of a newborn's foot from heel to toe is dorsiflexion of the great toe and fanning of the other toes. The provided source explains the physiological basis for this ^[1]. In the newborn, the pyramidal tract is not yet fully myelinated, meaning it does not exert the same inhibitory control over spinal motoneurons as it does in an older child or adult. Therefore, a primitive flexion synergy is brisk and involves all muscles that shorten the leg. The toe "extensors" are part of this synergy because their contraction also contributes to shortening the leg, making them physiological flexors in this context ^[1]. The upward movement of the big toe is a component of this mass flexion response, not a sign of upper motor neuron damage as it would be in an adult.

• Option 2: This describes the Moro reflex. While the Moro reflex is normal in a newborn, the description is incomplete and could be misinterpreted. A complete Moro reflex involves symmetric abduction and extension of the arms, fanning of the fingers, and then a return to midline with the arms coming together in an embrace-like motion, often followed by crying. The description of extending and bringing back the arms and legs is too vague and does not capture the characteristic "embrace" motion of the arms, making Option 1 a more precise and unequivocal description of a normal reflex.


• Option 3: This describes the palmar grasp reflex. While a tight grasp is normal, the description is a general observation. The Babinski reflex description in Option 1 is a highly specific, objective neurological sign with a clear developmental rationale tied to corticospinal tract maturation, making it a more definitive indicator of a normal primitive reflex in the context of this question.


• Option 4: This describes the asymmetric tonic neck reflex (ATNR), often called the "fencer's pose." While ATNR is a normal primitive reflex, it should not be obligatory. If the infant is stuck in this posture, it could indicate a neurological problem. The Babinski reflex is a more straightforward, consistently present, and easily elicited sign of a normal, immature nervous system in a 3-day-old, without the clinical caveats associated with ATNR.

For the NCLEX, you must know the timeline for the Babinski reflex. It is a normal finding in infants until the corticospinal tract matures, typically around 12-24 months of age. After this age, a positive Babinski sign (great toe dorsiflexion and toe fanning) is abnormal and indicates an upper motor neuron lesion. The underlying mechanism, as the source highlights, is the maturation of the pyramidal tract gaining control over spinal reflexes, which causes the toe "extensors" to disengage from the primitive flexion synergy. The toes then respond with plantar flexion, a segmental reflex, instead of the mass extension response ^[1]. This pathophysiological link between an anatomical finding and a clinical sign is a high-yield concept for the examination.