Primitive Reflexes

Primitive reflexes are involuntary motor responses that can be elicited after birth. Although these reflexes are important for survival, they gradually disappear within the 1st year of life due to their inhibition by the developing frontal lobe. Lesions in this area of the CNS may cause the restoration of primitive reflexes as a result of loss of inhibition.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

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Moro Reflex

  • Also known as the “startle reaction” 
  • Stimulus: sudden drop of an infant’s head 
  • Reaction: Infant extends arms and then pulls them in as if grasping; usually accompanied by crying.
  • Disappears normally by the age of 3 months but can last until 6 months of age
  • Absence could mean injury during birthing trauma ( clavicle fracture Clavicle fracture A clavicular fracture is a common fracture usually occurring because of trauma. The trauma may be direct or indirect and is generally of high energy, but it may occur secondary to low-energy trauma in the elderly. Clinical presentation includes pain localized to the clavicle, a palpable deformity over the fracture site, and crepitus. Clavicle Fracture or injury in the brachial plexus) or damage in the central nervous system Nervous system The nervous system is a small and complex system that consists of an intricate network of neural cells (or neurons) and even more glial cells (for support and insulation). It is divided according to its anatomical components as well as its functional characteristics. The brain and spinal cord are referred to as the central nervous system, and the branches of nerves from these structures are referred to as the peripheral nervous system. General Structure of the Nervous System.
Moro reflex

Moro reflex:
Sudden drop of an infant’s head causing the infant to extend their arms and then flex them as if grasping

Image by Lecturio.

Rooting Reflex

  • Stimulus: stroking infant’s cheek or mouth
  • Reaction: Infant orients toward the side of the face touched, turning neck and eyes in that direction.
  • Assists with breastfeeding Breastfeeding Breastfeeding is often the primary source of nutrition for the newborn. During pregnancy, hormonal stimulation causes the number and size of mammary glands in the breast to significantly increase. After delivery, prolactin stimulates milk production, while oxytocin stimulates milk expulsion through the lactiferous ducts, where it is sucked out through the nipple by the infant. Breastfeeding 
  • Disappears by 4 months of age
Rooting reflex

Rooting reflex:
When the infant’s cheek or mouth is stroked, they turn toward the side of the face that has been touched.

Image by Lecturio.

Suck-Swallow Reflex

  • Stimulus: touching roof of the mouth
  • Reaction: suckling
  • Associated with the rooting reflex in assisting with breastfeeding Breastfeeding Breastfeeding is often the primary source of nutrition for the newborn. During pregnancy, hormonal stimulation causes the number and size of mammary glands in the breast to significantly increase. After delivery, prolactin stimulates milk production, while oxytocin stimulates milk expulsion through the lactiferous ducts, where it is sucked out through the nipple by the infant. Breastfeeding 
  • Disappears by 4 months of age
Suck-swallow reflex

Suck-swallow reflex:
Contact with the infant’s soft palate Palate The palate is the structure that forms the roof of the mouth and floor of the nasal cavity. This structure is divided into soft and hard palates. Oral Cavity: Palate stimulates suckling.

Image by Lecturio.

Palmar Grasp Reflex

  • Stimulus: Slide the finger across the palm from lateral border.
  • Reaction: Infant closes their hand Hand The hand constitutes the distal part of the upper limb and provides the fine, precise movements needed in activities of daily living. It consists of 5 metacarpal bones and 14 phalanges, as well as numerous muscles innervated by the median and ulnar nerves. Hand around the finger.
  • Disappears by 6 months of age
  • Replaced by voluntary grasp at 45 weeks of age
Palmar grasp reflex

Palmar grasp reflex:
Sliding fingers across the infant’s palm elicits flexion of their fingers and grasping of the examiner’s finger.

Image by Lecturio.

Plantar Reflex (Babinski Sign)

  • Stimulus: plantar stimulation by firmly stroking the lateral aspect of the sole of the foot
  • Reaction: dorsiflexion of the large toe and fanning of the other toes
  • Disappears by 12 months of age
  • Also seen in patients with upper motor neuron lesion
Chaddock reflex

Babinski sign:
Plantar stimulation by firmly stroking the lateral aspect of the sole of the foot causes dorsiflexion of the large toe and fanning of the other toes.

Image: “Chaddock Reflex” by C. G. Goetz. License: Public Domain

Stepping Reflex

  • Stimulus: holding the infant so that only the soles of the feet touch the ground flat
  • Reaction: Infant places 1 foot in front of the other in a “walking pattern.”
  • Disappears by 2 months of age

Tonic Neck Reflex

  • Stimulus: Infant turns neck to 1 side.
  • Reaction: Arm Arm The arm, or "upper arm" in common usage, is the region of the upper limb that extends from the shoulder to the elbow joint and connects inferiorly to the forearm through the cubital fossa. It is divided into 2 fascial compartments (anterior and posterior). Arm on the side to which the infant turns straightens, contralateral arm bends in “fencing” posture
  • Disappears by 5–7 months of age
  • Reflex should be equal on both sides; asymmetric reflex may be a sign of pathology.

Galant Reflex

  • Stimulus: stroking along 1 side of the spine while the infant is held facing down
  • Reaction: lateral flexion of the lower limbs toward the side of stimulation
  • Disappears by 6 months of age
Galant reflex

Galant reflex:
Stroking along 1 side of the spine while the infant is held facing down causes lateral flexion of the lower limbs toward the side of stimulation.

Image: “Galant Reflex” by Ashley Arbuckle. License: CC BY 2.0

Summary

Table: Summary of primitive reflexes
Reflex Stimulus Reaction Disappears
Moro Pull up → drop Spreads arms → pulls them back 3–6 months
Rooting Stroke cheek/mouth. Orients mouth toward the stimulus 4 months
Palmar grasp Slide finger across the palm. Infant closes hand Hand The hand constitutes the distal part of the upper limb and provides the fine, precise movements needed in activities of daily living. It consists of 5 metacarpal bones and 14 phalanges, as well as numerous muscles innervated by the median and ulnar nerves. Hand around finger. 6 months
Babinski Firmly stroke the sole of the foot. Dorsiflexion of large toe; fanning of the other toes 12 months
Stepping Placing infant’s soles flat on surface while holding infant Walking motion 2 months
Tonic neck Turning neck to side Fencing posture 5–7 months
Galant Stroke along 1 side of the spine while infant faces down. Lateral movement of the limbs toward stimulated side 6 months

Clinical Relevance

Upper motor neuron lesions Upper motor neuron lesions Upper motor neurons (UMNs) and lower motor neurons (LMNs) combine to form a neuronal circuit for movement. UMN lesions cause damage to neurons above the motor nuclei of the cranial nerves in the brain stem or the anterior horn cells in the spinal cord. LMN lesions affect the nerve fibers traveling from the anterior horn of the spinal cord to the peripheral muscle. Upper and Lower Motor Neuron Lesions can cause disinhibition and deficits in judgement, orientation, and concentration. This type of lesion is also characterized by the restoration of primitive reflexes. The various reflexes manifesting in an adult can be helpful in identifying the location of the lesion in the CNS.

References

  1. Modrell AK, Tadi P. Primitive Reflexes. (2021). StatPearls. Treasure Island (FL): StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK554606/ 
  2. HealthyChildren.Org. (2021). Newborn Reflexes. https://www.healthychildren.org/English/ages-stages/baby/Pages/Newborn-Reflexes.aspx 

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