What is the startle reflex called in babies?

The Moro reflex was first described by Ernst Moro in 1918 and is a primitive infantile reflex that causes an involuntary protective motor response. The response produced is due to sudden stimulation and not due to the distance of the drop. It's mainly concerned with the extension and abduction of the upper extremities. It is elicited by pulling off the baby's arm in the supine position and then letting the arms go to produce the sensation of falling. It is easily confused with a startle pattern or reflex. This reflex is said to be of labyrinthine origin.

It is important to note that it can't be elicited in premature babies due to lower muscle tone which further does not allow resistance to passive movements. The absence and hyper-response of this reflex are of diagnostic value.[1]

Head Drop Method: Supine position. Suspend the baby horizontally, in a symmetrical supine position such that the therapist's one hand behind the chest and the other supports the head. The infant's head should be in the midline position.[2]

It is important to guarantee that both the infant's hands are open at the moment of elicitation of the reflex so as not to produce an asymmetrical response. Also, ensure that the baby is awake and not crying during the examination.

Baby Drop Method: Same as the head drop method.

Head Drop Method: Dropping the head of the baby by a few centimetres.

Baby Drop Method: The therapist lowers their hands rapidly about 10 to 20 cm and brings them to an abrupt halt.

Subcutaneous Stimulus: Painful stimulus to the subcutaneous tissue of the epigastrium. ( considered to be a more sensitive technique)

Normal Response[edit | edit source]

Initial Phase: Abduction of the upper extremities and extension of the arms. The fingers extend, and there is a slight extension of the neck and spine.

After Phase: Arms adduct and the hands come to the front of the body before returning to the infant's side.

Abnormal Response[edit | edit source]

The disintegration of the reflex within 2 to 3 months of age.

Persistence of the response beyond 6 months of age.

Asymmetrical response.

This reflex can be stimulated in all neonates during the first 12 weeks of age and disintegrates by 6 months of age.

[3]

The examiner holds the infant in the supine position and drops the head slowly downwards. Abduction of upper extremities followed by extension of arms with a fingers extension is seen.

This reflex is primarily elicited with the help of vestibular nuclei. It is mediated by the brainstem and therefore its centre seems to be in the lower region of the pons to the medulla. The efferent pathways of the response seem to originate in the vestibulospinal and/or reticulospinal neurons and the reflex movement is generated by the subcortical structures without cortical participation.[2]

The Difference between Moro and Startle Reflex[edit | edit source]

The startle reflex, the response to a sudden stimulus, is one of the defensive reactions and consists essentially of flexion movements. It differs from the Moro response which is characterized by extension.

The startle reaction is induced by an auditory stimulus which shows clear habituation in premature infants, whereas the Moro reflex does not stimulate due to any auditory cues.

The startle reaction can not be elicited in anencephalic newborns, while the Moro reflex is always elicited in these infants.

Reflexes are involuntary movements or actions. Some movements are spontaneous, occurring as part of the baby's usual activity. Others are responses to certain actions. Reflexes help identify normal brain and nerve activity. Some reflexes occur only in specific periods of development. The following are some of the normal reflexes seen in newborn babies:

Root reflex 

This reflex begins when the corner of the baby's mouth is stroked or touched. The baby will turn his or her head and open his or her mouth to follow and "root" in the direction of the stroking. This helps the baby find the breast or bottle to begin feeding.

Suck reflex

Rooting helps the baby become ready to suck. When the roof of the baby's mouth is touched, the baby will begin to suck. This reflex does not begin until about the 32nd week of pregnancy and is not fully developed until about 36 weeks. Premature babies may have a weak or immature sucking ability because of this. Babies also have a hand-to-mouth reflex that goes with rooting and sucking and may suck on fingers or hands.

Moro reflex 

The Moro reflex is often called a startle reflex because it usually occurs when a baby is startled by a loud sound or movement. In response to the sound, the baby throws back his or her head, extends out the arms and legs, cries, then pulls the arms and legs back in. A baby's own cry can startle him or her and trigger this reflex. This reflex lasts about 5 to 6 months.

Tonic neck reflex

When a baby's head is turned to one side, the arm on that side stretches out and the opposite arm bends up at the elbow. This is often called the "fencing" position. The tonic neck reflex lasts about 6 to 7 months.

Grasp reflex 

Stroking the palm of a baby's hand causes the baby to close his or her fingers in a grasp. The grasp reflex lasts until about 5 to 6 months of age.

Babinski reflex

When the sole of the foot is firmly stroked, the big toe bends back toward the top of the foot and the other toes fan out. This is a normal reflex up to about 2 years of age.

Step reflex

This reflex is also called the walking or dance reflex because a baby appears to take steps or dance when held upright with his or her feet touching a solid surface.

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