The Mendel-Bechterew reflex is a foot reflex from the Babinski group that is categorized as a pyramidal tract sign. The pathologic reflex movement may suggest damage to the central motor neurons. Such damage presents, for example, in the context of amyotrophic lateral sclerosis (ALS).
What is the Mendel-Bechterew reflex?
For example, when the top of their foot is brushed, all of their toes move toward the bottom of their foot. This reflex movement is the Mendel-Bechterew reflex. The Mendel-Bechterew reflex is a pathological reflex of the foot limbs. The reflex movement belongs to the Babinski group and is therefore a so-called pyramidal tract sign. Neurology knows this reflex group as a symptom of diseases of the motoneurons in the central nervous system. The motoneurons are the superior switching points for voluntary and reflex motor activity. The lower motoneuron is located in the anterior horn of the spinal cord on the so-called pyramidal tracts. From here, nerve impulses are conducted efferently from the central nervous system to the organs of success and the skeletal musculature. The Mendel-Bechterew reflex was named after Vladimir Mikhailovich Bekhterev. The Russian neurologist first associated the reflex with a pathological value in the 19th century. In connection with its discoverer, the Mendel-Bechterew reflex is also included in the group of ankylosing spondylitis reflexes. All ankylosing spondylitis reflexes have pathological value and can be traced back to Bechterew as the first describer. In addition to the Mendel-Bechterew reflex, the pupillary reflex, for example, is also included in the ankylosing spondylitis reflexes.
Function and task
The human body uses motor reflexes to protect itself from injury and functional loss. Most reflexes are therefore also called protective reflexes. Examples of such reflex movements are the cough reflex to protect against choking and the eyelid-closing reflex to protect the eyeball. All reflexes are triggered by so-called triggers. These triggers are perceptions from one of the five human perceptual systems. The visual system in particular performs trigger functions in connection with reflexes. For example, when the eyes see an object approaching the face, the defensive reflex of the arms is initiated. Evasion would also be a motor reflex in this context. In the cough reflex, the triggers are not specific perceptions of the eyes, but of the mechanoreceptors in the mucous membranes of the respiratory tract. When these sensory cells register strong irritation, they trigger reflex coughing. In this way, they catapult food particles and liquids back out of the respiratory tract if the person swallows. The reflex system is largely uncontrollable because it consists of involuntary movements. Throughout life, the reflex system changes. Adults therefore have fewer reflexes than a baby, for whom reflex movements are still essential for survival. Infants, for example, automatically suckle at their mother’s breast long before they could do so voluntarily. This reflex regresses after the first year of life, since it is then no longer needed for survival. The reflexes of the Babinski group are also physiological reflex movements for infants up to one year of age. Consequently, they have no pathological value. For an adult, however, the pyramidal tract signs are pathological and resemble regression, as may be present with damage to the central motoneurons. As noted at the outset, the motor neurons are the master control center for extensive movement. For example, an infant cannot yet move the muscles of the individual foot limbs individually, but only as a group. When the back of her foot is brushed, for example, all the toes move toward the sole of the foot. This reflex movement is the Mendel-Bechterew reflex. Thanks to the motoneurons, however, it is possible for humans from about one year of age to make specific movements of individual foot limbs. From this age, the central motoneurons connect the impulses as action potentials to individual muscle spindles of the skeletal muscles. Thus, if the Mendel-Bechterew reflex can be triggered in an adult, this points to a lack of higher-level control by the central motoneurons.
Diseases and complaints
Like all other pyramidal tract signs, the Mendel-Bechterew reflex is a symptom of a neurologic lesion involving the motor neurons. For this reason, the pathologic reflex is primarily considered in neurologic diagnosis.Reflex examination has become a standard diagnostic procedure in neurology. Nevertheless, the reliability of diagnostic criteria from the Babinski group is viewed critically today. Thus, a single reflex from the Babinski group is by far no longer sufficient to speculate about motor neuron damage. The Mendel-Bechterew reflex is therefore no longer of diagnostic value. The same applies to all other reflexes from the group of pyramidal pathway signs. Nevertheless, reflexes of the Babinski group can give the neurologist a first suspicion of the localization of a lesion in the central nervous system. If there is a lesion of the first motoneuron, accompanying signs are mainly spasticity. If, on the other hand, the second motoneuron is affected by damage, the primary symptom is usually muscle weakness or unsteadiness of movement. Based on these correlations, making a diagnosis of a specific disease is still a challenge, as various neurological diseases can damage the motor neurons. For example, the autoimmune disease multiple sclerosis causes immunological inflammation in the brain and spinal cord nerve tissue, which can lead to motor neuron damage. Similarly, ALS can cause a motoneuronal lesion. In this degenerative disease, piece by piece the tissue in the motor nervous system is broken down. In addition to diagnostic value, all pyramidal tract signs also have prognostic value. For example, neurologists tend to speak of an unfavorable course of multiple sclerosis if pyramidal tract signs are already present at the onset of the disease. Even as a prognostic criterion, however, Babinski group reflexes are not 100% reliable criteria.
