Of the symmetrical-tonic neck reflex is an early childhood reflex that is physiological up to the third month of life. In the supine position, the examiner bends the child's head and thereby stimulates a reflex movement of the arms and legs. The persistence of the reflex beyond the first three months of life indicates neurological disorders.
What is the symmetrical-tonic neck reflex?
Reflexes are automatic and involuntary body responses to a particular stimulus. Infants and young children have a number of reflexes that adults no longer have. These reflex stimulus responses are known as early childhood reflexes. In the course of further maturation, these reflexes regress.
It is only after birth that the central motor neurons are fully developed, which serve as a superordinate control authority and make many of the early childhood reflexes disappear. Individual reflexes from the group of early childhood reflexes occur in certain weeks or months of life and regress at a certain point in time.
The symmetrical-tonic neck reflex is a reflective movement from the group of early childhood reflexes. It is present until the third month of life. This must be distinguished from the asymmetric-tonic neck reflex, which disappears between the sixth and seventh week of life.
In the symmetrical-tonic neck reflex, the triggering stimulus corresponds to an extension or flexion of the head, which is answered by the child's body with an automatic flexion or extension of the arms and legs.
Function & task
A large number of all human reflex movements are protective reflexes that serve not least for survival. The early childhood reflexes are also geared towards survival, such as the sucking reflex, in which the child responds to a touch stimulus near the mouth with sucking movements.
Each reflex is based on a so-called reflex arc. The first instance of this reflex arc is always a sensory perception. With the sucking reflex, this sensory perception corresponds to a sensation of the skin's sensory cells. The reflex-triggering perception migrates into the central nervous system via afferent nerve tracts. In the spinal cord, the excitation is switched to efferent nerve pathways, which lead from the central nervous system to the body periphery. This is how arousal reaches the success system. This system corresponds to the muscle that performs the reflex movement.
To trigger the symmetrical-tonic neck reflex, the child is in the supine position. The examiner moves the child's head into flexion, i.e. flexion. The sensory cells of deep sensitivity report the bending of the head to the central nervous system via afferent nerve tracts. Thanks to the deep sensitivity, the central nervous system is permanently informed about body positions and muscle movements.
The most important sensory cells in the system are the muscle spindle and the Golgi tendon apparatus. In the symmetrical-tonic neck reflex, the action potential from nerve excitation is switched to efferent nerve pathways that lead to the muscles of the arms and legs. Once the excitation reaches the nerves near the muscles, it is transmitted to the muscles themselves through the motor endplate. The muscles of the arms are stimulated to contract and bend the arm. At the same time, the muscles of the legs are stimulated to extend, so that the child's legs stretch.
When the examiner moves the child's head from flexion back into extension, the reverse motion response is triggered. Stretching the head stimulates the arms to stretch and the legs to flex. The symmetrical-tonic neck reflex is characterized by the symmetrical cooperation of the right and left side of the body.
As soon as the child begins to crawl, the reflex should have subsided. While the reflex muscle work on a neck movement stimulus still makes sense in the first three months, the reflex prevents crawling and accommodation training after this time.
Illnesses & ailments
Reviewing early childhood reflexes is an important tool in assessing child development. As part of the preventive medical check-up, reflexes are checked regularly in childhood. If the symmetrical-tonic neck reflex is absent or reduced in the first few months, this can indicate, for example, nerve damage to the nerves of the reflex arc.
While the asymmetrical occurrence or the absence of the symmetrical-tonic neck reflex in the first three months of life indicates neurological disorders, after the first three months of life the persistence of the early childhood reflex is an indicator of neurological disorders.
If the reflex persists, consequences such as poor posture and weak body tension when sitting and standing can result. The child's attention is disturbed. Sitting positions can hardly be maintained and require a high level of concentration.
In exceptional cases, the symmetrical-tonic neck reflex can suddenly and unexpectedly reappear later in a patient's life. In this context, the reflex is a sign of central nervous system disorders.
It is possible that the patient's overall control of movement is impaired by a pathological process. Such processes can involve accidental injuries to the neck area. Tumors, spinal cord infarctions, bacterial or autoimmunological inflammations and degenerative diseases of the central nervous system can also be responsible for a suddenly recurring symmetrical-tonic neck reflex.
As a rule, the sole proof of a persistent symmetrical-tonic neck reflex is not sufficient to prove, for example, damage to the superordinate controlling motor neurons. Evidence of the persistence of several reflexes from the group of early childhood reflexes is more informative in this context. The further clarification mainly includes imaging of the spine and brain.
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