What reflex is demonstrated when an infant startles in response to a loud sound or sudden movement?

The Moro reflex is indeed the correct answer as it specifically refers to the startle response observed in infants. This reflex is characterized by the infant's abrupt extension of the arms and legs, followed by their retraction, when they experience a sudden noise or movement. This response is believed to be a protective mechanism, allowing the infant to react to potential threats in their environment.

The Moro reflex typically appears at birth and can last until around 4 to 6 months of age when it usually diminishes as the child grows and starts developing more voluntary movements and stability. Understanding this reflex is important in pediatric development assessments, as it provides insight into the neurological development of the infant.

The other reflexes listed serve different functions: the Babinski reflex involves the splaying of toes when the sole of the foot is stimulated, commonly assessed to evaluate neurological function; the rooting reflex is related to searching for the breast or bottle when the infant's cheek is stroked; while the grasp reflex is characterized by an infant's tendency to grasp objects placed in their hand. Each of these reflexes plays a distinct role in early development, but the stimulus described in the question aligns specifically with the Moro reflex.