Mendel-Bechterew reflex

At the Mendel-Bechterew reflex it is a foot reflex from the Babinski group, which is counted among the pyramid orbit signs. The pathological reflex movement can indicate damage to the central motor neurons. Such damage occurs, for example, in the context of amyotrophic lateral sclerosis (ALS).

What is the Mendel-Bechterew reflex?

The Mendel-Bechterew reflex is a pathological reflex of the limbs. The reflex movement belongs to the Babinski group and is therefore a so-called pyramid orbit sign. Neurology knows this reflex group as a symptom in diseases of the motor neurons in the central nervous system.

The motor neurons are the superordinate switching points for the voluntary and reflex motor skills. The lower motor neuron lies in the anterior horn of the spinal cord on the so-called pyramidal tracts. From here, nerve impulses are efferent from the central nervous system to the successive organs and the skeletal muscles.

The Mendel-Bechterew reflex was named after Vladimir Michailowitsch Bechterew. 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 Bechterew reflexes. All Bechterew reflexes have disease value and go back to Bechterew as the first to describe it. In addition to the Mendel-Bechterew reflex, the pupil reflex is also one of the Bechterew reflexes.

Function & task

The human body uses motor reflexes to protect itself from injuries and functional losses. Most of the reflexes are therefore also called protective reflexes. Examples of such reflex movements are the cough reflex as protection against suffocation 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 perception systems. The visual system in particular takes on trigger functions in connection with reflexes. For example, if the eyes see an object approaching the face, the defensive reflex of the arms is initiated. Dodging 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 airways. When these sensory cells register strong irritation, they trigger reflex cough. This catapults food components and fluids out of the airways again if the person chokes.

The reflex system is largely uncontrollable because it consists of involuntary movements. The reflex system changes in the course of life. Adults therefore have fewer reflexes than a baby, for whom the reflex movements are still vital. Infants, for example, automatically suckle on their mother's breast long before they can do so at will. This reflex regresses after the first year of life, as it is then no longer needed for survival.

The reflexes of the Babinski group are also physiological reflex movements for babies up to one year of age. As a result, they have no disease value. For an adult, however, the pyramidal trajectory signs are pathological and resemble a retrograde development, as can be the case with damage to the central motor neurons.

As mentioned at the beginning, the motor neurons are the superordinate switching point for extensive movement sequences. For example, an infant cannot yet move the muscles of the individual limbs individually, but only in a group. If the back of the foot is coated, all toes move towards the sole of the foot, for example. This reflex movement is the Mendel-Bechterew reflex.

Thanks to the motor neurons, people from around one year of age are able to specifically move individual limbs. From this age on, the central motor neurons connect the impulses as action potentials to individual muscle spindles of the skeletal muscles. If the Mendel-Bechterew reflex can be triggered in an adult, then this indicates a lack of superordinate control by the central motor neurons.

Illnesses & ailments

Like all other pyramidal signs, the Mendel-Bechterew reflex is the symptom of a neurological lesion that affects the motor neurons. For this reason, the pathological reflex is primarily taken into account in neurological diagnostics.

The reflex examination has meanwhile become a standard diagnostic procedure in neurology. Nevertheless, the reliability of diagnostic criteria from the Babinski group is viewed critically today. A single reflex from the Babinski group is now by no means sufficient to speculate about damage to the motor neurons. The Mendel-Bechterew reflex no longer has a diagnostic value. The same applies to all other reflexes from the group of pyramidal orbit signs.

Nonetheless, reflexes of the Babinski group can give the neurologist an initial suspicion of the location of a lesion in the central nervous system. A lesion of the first motor neuron is accompanied by spasticity in particular. If, on the other hand, the second motor neuron is damaged, the primary symptom is usually muscle weakness or insecurity.

Making a diagnosis of a particular disease based on these relationships is still a challenge, as various neurological diseases can damage motor neurons. The autoimmune disease multiple sclerosis, for example, causes immunological inflammation in the brain and in the nerve tissue of the spinal cord, which can damage the motor neurons. Similarly, ALS can cause a motor neuronal lesion. In this degenerative disease, the tissue in the motor nervous system is broken down bit by bit.

In addition to the diagnostic value, all pyramidal signs also have prognostic value. For example, the neurologist tends to speak of an unfavorable course of multiple sclerosis if signs of a pyramidal path are already present at the onset of the disease. Even as a prognostic criterion, the Babinski Group's reflexes are not 100 percent reliable criteria.