The radial periosteal reflex or brachial radialis reflex is a self-reflex of the arm. Medicine calls a reflex its own reflex when irritation and reaction take place in the same organ. The radius-periosteal reflex triggers a blow on the radius. The radius is a bone of the forearm, which is also called a spoke.
The radius is a so-called tubular bone: the medullary cavity of the bone forms a uniform tube inside, in which the bone marrow is located. Together with the Ulna (Elle), the radius forms the skeleton of the forearm.
To trigger the radial periosteal reflex, the forearm must be at an angle to the upper arm. He must not be turned outwards or inwards. An outward-facing position refers to medicine as a suspension, while the inward-turned posture of the forearm is called pronation. A strike against the radius triggers the radius-periosteal reflex, resulting in the pronation of the hand and forearm.
The radius periosteal reflex is based on a simple neurological interconnection. Receptors on the forearm register the impact on the bone: The mechanical stimulation causes the sensory nerve cell to fire, ie to produce a signal. This happens by changing the electrical charge of the neuron.
Through changes in the cell membrane, the ion ratio shifts between the interior and exterior of the cell and the neuron becomes depolarized. As a summed electrical potential, the neuron forwards the stimulation via its axon. At the end of the nerve cell there is an interface between the first and a second cell. This interface refers to the natural sciences as a synaptic cleft. The signal passes through the synaptic cleft by first being translated into a chemical form: the electrical voltage of the first nerve cell causes the release of neurotransmitters. Neurotransmitters are messenger substances that enter the synaptic cleft and reach the second nerve cell at the other end. There, the neurotransmitters bind to specialized receptors, to which they fit like a key in a lock. The occupied receptors now also trigger a change in the electrical charge in the second nerve cell by opening ion channels in the cell membrane: the second nerve cell depolarises and the information about the stimulation has successfully passed to the second neuron.
In the case of the radius-periosteal reflex, this compound is monosynaptic: only a single synapse is involved in the transmission of the signal from the receptor to the spinal cord. Biology calls this forwarding of signals also as afference, from the Latin word for "afferer" ("affere"). On the opposite path, the efferent ("outgoing") nerve tract, the motor neuron then sends the signal for muscle contraction. This signal is directed to the upper arm spokes muscle (brachioradialis muscle). The upper arm spokes muscle is a skeletal muscle that is located in the upper arm and is directed to the thumb facing side. By contracting the upper arm spokes muscle, the associated tendon shortens and bends the forearm.
Neurology refers to the nerve tracts that are responsible for the radius periosteum reflex, with the numbers C4 and C6. In addition, the radial nerve (radial nerve) participates in the neuronal transfer of information. Like all reflexes, the radius-periosteal reflex does not involve the brain; Therefore, humans can not consciously control, suppress or deliberately trigger it.
When checking the radius periosteal reflex, doctors compare whether the reaction on both sides is the same. This comparison minimizes misdiagnosis, allowing the study to account for interindividual differences in responsiveness.
The absence of radial periosteal reflex may indicate radial paralysis. It is a paralysis of the arm that attacks the wrist and finger extensors. Damage to the nerves of the upper arm, especially the radial nerve, is responsible for this. The radial paralysis manifests itself in a characteristic finger posture: The relatively high muscle tension bends the muscles of the fingers and the wrist slightly, so that the impression arises that the affected person wants to point to something or hand to kiss. For this reason, the vernacular calls this attitude also kiss or fall hand.
The cause of radial paralysis often lies in a fracture of the upper arm or other severe, mechanical action. It can also arise, for example, if the affected person is immobile on the side for a long time, as is the case in anesthetized or bedridden patients. In this case, the body weight presses on the radial nerve for a long time, possibly causing damage. The therapy of radial paralysis depends on the causes in the individual case; the damaged nerve can under certain circumstances be reconstructed or regenerate itself by sufficient protection.
The absence of the radial periosteum reflex is also potentially the symptom of myotonic disease. It is a group of different muscle disorders that are characterized by prolonged muscle tension and delayed relaxation. This group includes various syndromes of muscle atrophy. Myotonic dystrophy type 1, for example, is a genetic disease characterized by muscle weakness, arrhythmia and hormonal abnormalities. In her and similar diseases, especially the treatment of symptoms is in the foreground.