Asymmetrical tonic neck reflex (ATNR) in a two-week-old female

The asymmetrical tonic neck reflex (ATNR) is a

primitive reflex Primitive reflexes are reflex actions originating in the central nervous system that are exhibited by normal infants, but not neurologically intact adults, in response to particular stimuli. These reflexes are suppressed by the development of the f ...

found in newborn humans that normally vanishes around 6 months of age. It is also known as the bow and arrow or "fencing reflex" because of the characteristic position of the infant's arms and head, which resembles that of a fencer. When the face is turned to one side, the arm and leg on that side extend, and the arm and leg on the opposite side flex. It is more likely to be seen in premature infants than full-term babies. It is rare in newborns but can be stimulated from infants to up to 3 months old. It is believed to help develop hand-eye coordination and help with awareness of both sides of the body The presence of the ATNR, as well as other primitive reflexes, such as the

tonic labyrinthine reflex The tonic labyrinthine reflex (TLR) is a primitive reflex found in newborn humans. With this reflex, tilting the head back while lying on the back causes the back to stiffen and even arch backwards, the legs to straighten, stiffen, and push togethe ...

(TLR), beyond the first six months of life may indicate that the child has developmental delays, at which point the reflex is atypical or abnormal. For example, in children with

cerebral palsy Cerebral palsy (CP) is a group of movement disorders that appear in early childhood. Signs and symptoms vary among people and over time, but include poor coordination, stiff muscles, weak muscles, and tremors. There may be problems with sensa ...

, the reflexes may persist and even be more pronounced. As abnormal reflexes, both the ATNR and the TLR can cause problems for the growing child. The ATNR and TLR both hinder functional activities such as rolling, bringing the hands together, or even bringing the hands to the mouth. Over time, both the ATNR and TLR can cause serious damage to the growing child's joints and bones. The ATNR can cause the spine to curve (

scoliosis Scoliosis is a condition in which a person's spine has a sideways curve. The curve is usually "S"- or "C"-shaped over three dimensions. In some, the degree of curve is stable, while in others, it increases over time. Mild scoliosis does not t ...

). Both the ATNR and TLR can cause

subluxation A subluxation is an incomplete or partial dislocation of a joint or organ. According to the World Health Organization (WHO), a subluxation is a "significant structural displacement", and is therefore always visible on static imaging studies, suc ...

of the femoral head or

dislocation In materials science, a dislocation or Taylor's dislocation is a linear crystallographic defect or irregularity within a crystal structure that contains an abrupt change in the arrangement of atoms. The movement of dislocations allow atoms to sl ...

of the femoral head as it completely moves out of the

hip socket The acetabulum (), also called the cotyloid cavity, is a concave surface of the pelvis. The head of the femur meets with the pelvis at the acetabulum, forming the hip joint. Structure There are three bones of the ''os coxae'' (hip bone) that ...

. When abnormal reflexes persist in a child, evidence suggests early intervention involving extensive physical therapy as the most beneficial course of treatment. The

fencing response The fencing response is an unnatural position of the arms following a concussion. Immediately after moderate forces have been applied to the brainstem, the forearms are held flexed or extended (typically into the air) for a period lasting up to sev ...

occurs in adults as a result of mechanical forces applied to the head, typically associated with contact sports. The fencing response is transient and indicates moderate forces applied to the

brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is cont ...

, resulting in a

traumatic brain injury A traumatic brain injury (TBI), also known as an intracranial injury, is an injury to the brain caused by an external force. TBI can be classified based on severity (ranging from mild traumatic brain injury TBI/concussionto severe traumatic b ...

References

* * Diagnostic neurology Neonatology Reflexes {{Pediatrics-stub

See also

References