The symmetrical tonic neck reflex (STNR) is a
primitive reflex that normally emerges during the first month of an infant's life and is diminished by the age of 9–10 months.
It is a bridging or transitional
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 conti ...
reflex that is an important
developmental stage and is necessary for a baby to transition from lying on the floor to quadruped
crawling or
walking
Walking (also known as ambulation) is one of the main gaits of terrestrial locomotion among legged animals. Walking is typically slower than running and other gaits. Walking is defined as an " inverted pendulum" gait in which the body vaults o ...
.
In order to progress beyond this development stage, the baby needs to have been successful in unlinking the automatic movement of the head from the automatic movement of the arms and legs.
The STNR is normally fully developed by 6–8 months and significantly diminished by 2–3 years. If this reflex is retained beyond 2–3 years to such a degree that it "modifies voluntary movement", the child is considered to have "immature and abnormal reflex development", and this can have broad effects on the child's later development.
Testing
The symmetrical tonic neck reflex can be tested by placing the child in quadruped position on the floor and passively flexing the head forward and then extend it backwards. The expected response would be forward head flexion producing flexion of the upper extremities and extension of the lower extremities while extension of the head will produce extension of the upper extremities and flexion of the lower extremities.
Significance
This reflex can help the child to come to quadruped or crawling position but does not allow crawling because when the neck flexes forward, the upper limbs flex and lower limbs go into extension. This reflex is not normally easily seen or elicited in normal infants but may be seen in an exaggerated form in many 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, spasticity, stiff muscles, Paresis, weak muscles, and tremors. There may b ...
.
See also
*
Asymmetrical tonic neck reflex
References
Reflexes
Pediatrics
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