Startle reflex

The Moro reflex, also known as the startle reflex, is one of the infantile reflexes. It may be observed in incomplete form in premature birth after the 28th week of gestation, and is usually present in complete form by week 34 (third trimester). It is normally lost by the 6th month of life postpartum. It was discovered and first described by Austrian pediatrician Ernst Moro (1874-1951).

This reflex is a response to unexpected loud noise or when the infant feels like it is falling. It is believed to be the only unlearned fear in human newborns. The little Albert study used the startle reflex in the famous classical conditioning experiment to make him fear white fuzzy things.

The primary significance of this reflex is in evaluating integration of the central nervous system (CNS), since the reflex involves 4 distinct components:
 * 1) Startle
 * 2) spreading out the arms (abduction)
 * 3) unspreading the arms (adduction)
 * 4) Crying (usually)

Absence of any component (except crying) or any asymmetry in the movements is abnormal, as is persistence of the reflex in older infants, children and adults.

The origin of this reflex can be found in that fact that primate infants of our ancestors clung to their mother's fur soon after birth, giving their mother the advantage of having her hands free to forage for food and such. If human babies are falling backward with their head their innate reflex will be to stretch out the arms to grab and cling to their mother.