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Primitive Reflexes

Primitive reflexes are involuntary motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology 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 Frontal The bone that forms the frontal aspect of the skull. Its flat part forms the forehead, articulating inferiorly with the nasal bone and the cheek bone on each side of the face. Skull: Anatomy lobe. Lesions in this area of the CNS may cause the restoration of primitive reflexes as a result of loss of inhibition.

Last updated: Sep 22, 2022

Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Moro Reflex

  • Also known as the “startle reaction” 
  • Stimulus: sudden drop of an infant’s head (sudden movement) or loud noise
  • 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 Mean Mean is the sum of all measurements in a data set divided by the number of measurements in that data set. Measures of Central Tendency and Dispersion 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 Brachial Plexus The large network of nerve fibers which distributes the innervation of the upper extremity. The brachial plexus extends from the neck into the axilla. In humans, the nerves of the plexus usually originate from the lower cervical and the first thoracic spinal cord segments (c5-c8 and T1), but variations are not uncommon. Peripheral Nerve Injuries in the Cervicothoracic Region) or damage in the central nervous system Central nervous system The main information-processing organs of the nervous system, consisting of the brain, spinal cord, and meninges. Nervous System: Anatomy, Structure, and Classification.
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 Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess 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 Roof of the mouth 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. Palate: Anatomy
  • 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. Palate: Anatomy 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: Anatomy 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 Flexion Examination of the Upper Limbs 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 Foot The foot is the terminal portion of the lower limb, whose primary function is to bear weight and facilitate locomotion. The foot comprises 26 bones, including the tarsal bones, metatarsal bones, and phalanges. The bones of the foot form longitudinal and transverse arches and are supported by various muscles, ligaments, and tendons. Foot: Anatomy
  • Reaction: dorsiflexion of the large toe and fanning of the other toes
  • Disappears by 12 months of age
  • Also seen in patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship with upper motor neuron lesion Upper Motor Neuron Lesion Motor Neuron Lesions
Newborn reflex - babinski

Babinski sign Babinski sign A reflex found in normal infants consisting of dorsiflexion of the hallux and abduction of the other toes in response to cutaneous stimulation of the plantar surface of the foot. In adults, it is used as a diagnostic criterion, and if present is a neurologic manifestation of dysfunction in the central nervous system. Posterior Cord Syndrome:
Plantar stimulation by firmly stroking the lateral aspect of the sole of the foot Foot The foot is the terminal portion of the lower limb, whose primary function is to bear weight and facilitate locomotion. The foot comprises 26 bones, including the tarsal bones, metatarsal bones, and phalanges. The bones of the foot form longitudinal and transverse arches and are supported by various muscles, ligaments, and tendons. Foot: Anatomy causes dorsiflexion of large toe and fanning of the other toes.

Image by Lecturio.

Stepping Reflex

  • Stimulus: holding the infant so that only the soles of the feet touch the ground flat
  • Reaction: Infant places 1 foot Foot The foot is the terminal portion of the lower limb, whose primary function is to bear weight and facilitate locomotion. The foot comprises 26 bones, including the tarsal bones, metatarsal bones, and phalanges. The bones of the foot form longitudinal and transverse arches and are supported by various muscles, ligaments, and tendons. Foot: Anatomy in front of the other in a “walking pattern.”
  • Disappears by 2 months of age

Tonic Neck Reflex

  • Stimulus: Infant turns neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess 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: Anatomy on the side to which the infant turns straightens, contralateral 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: Anatomy 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.
Tonic neck reflex

Asymmetrical tonic neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess reflex in a 2-month-old baby:
Extension Extension Examination of the Upper Limbs of the 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: Anatomy and leg Leg The lower leg, or just “leg” in anatomical terms, is the part of the lower limb between the knee and the ankle joint. The bony structure is composed of the tibia and fibula bones, and the muscles of the leg are grouped into the anterior, lateral, and posterior compartments by extensions of fascia. Leg: Anatomy on the face side with flexion Flexion Examination of the Upper Limbs of the 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: Anatomy and leg Leg The lower leg, or just “leg” in anatomical terms, is the part of the lower limb between the knee and the ankle joint. The bony structure is composed of the tibia and fibula bones, and the muscles of the leg are grouped into the anterior, lateral, and posterior compartments by extensions of fascia. Leg: Anatomy on the skull Skull The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. Skull: Anatomy side

Image: “Asymmetrical tonic neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess reflex (ATNR) at Two Months” by Mjlissner. License: Public Domain

Galant Reflex

  • Stimulus: stroking along 1 side of the spine Spine The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. Vertebral Column: Anatomy while the infant is held facing down
  • Reaction: lateral flexion Flexion Examination of the Upper Limbs of the lower limbs toward the side of stimulation
  • Disappears by 6 months of age
Galant reflexe

Galant reflex
Stroking along one side of the spine Spine The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. Vertebral Column: Anatomy while the infant is held facing down causes lateral flexion Flexion Examination of the Upper Limbs of the lower limbs towards the side of stimulation.

Image by Lecturio.

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: Anatomy around finger. 6 months
Babinski Firmly stroke the sole of the foot Foot The foot is the terminal portion of the lower limb, whose primary function is to bear weight and facilitate locomotion. The foot comprises 26 bones, including the tarsal bones, metatarsal bones, and phalanges. The bones of the foot form longitudinal and transverse arches and are supported by various muscles, ligaments, and tendons. Foot: Anatomy. 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 Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess Turning neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess to side Fencing posture 5–7 months
Galant Stroke along 1 side of the spine Spine The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. Vertebral Column: Anatomy 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. Motor Neuron Lesions can cause disinhibition and deficits in judgement, orientation Orientation Awareness of oneself in relation to time, place and person. Psychiatric Assessment, 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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