Osteotendinous reflexes: what are they, how do they work, and associated pathologies?

What are osteotendinous reflexes and what is their importance in medical examinations?

In neuroscience, a reflex is the nervous activity developed in the spinal cord (and brainstem) that consists of an involuntary response to a sensory stimulus, whether internal or external. Generally, we associate reflexes with rapid and uncontrollable jerky movements, but another example of this activity is also the activation of a gland and the secretion of a given compound into the bloodstream.

In any case, on a general level every reflex is involuntary, unplanned, sequential and practically instantaneous. The triggering of a reflex is achieved by neural pathways and reflex arcs, i.e., the nerve pathway that runs through the vertebral arch and controls a given reflex act. It should be noted at this point that there are 2 types of reflex arcs: autonomic (affecting internal organs) and somatic (affecting muscles).

With all this information, we are able to paint a general picture that allows us to understand what reflexes are and what they are for. However, in this opportunity we are going to talk specifically about the osteotendinous reflexes. osteotendinous reflexesThe osteotendinous reflexes, muscle contractions in response to stretching within a muscle.

What are osteotendinous reflexes?

In humans, when a muscle is struck forcefully, it immediately contracts due to a reflex arc composed of 2 neurons, which also involve the segment of the spinal trunk that innervates the muscular structure analyzed. These are the osteotendinous reflexes themselves. For this special type of reflex to occur, the following physiological elements must be present:

• Receptor: in this case we are dealing with muscle receptors (spindles), which will capture the sudden "stretching" of the unit after the external stimulus.
• Afferent nerve fiber: this is constituted by the axon of the sensory neuron. It is located in the spinal ganglia and innervates the neuromuscular spindle (sensory receptors within the muscle belly).
• Integrating center: located in the spinal cord and where the synapse between the afferent and efferent neuron occurs.
• Efferent nerve fiber: it is the axon of the motor neuron. It carries the motor nerve signals from the anterior horn of the spinal cord to the muscles.
• Muscle unit: it is the one that carries out the actual contraction response and is innervated by the efferent fiber. In other words, it is the structure that responds to the external stimulus.

The osteotendinous reflexes that are usually explored, depending on the stimulated area, are the bicipital, tricipital, stylo-radial, ulnar, patellar and Achilles reflexes.. The type of reflex and the response shown always reveal something about the state of the elements of the nervous system involved in its appearance.

When one wants to evaluate the state of the reflex arches, the practitioner applies a light force on an area of the body, which results in a slight elongation of the muscle fiber. This act activates the neuromuscular spindle, formed by a set of sensory receptors inside the muscle that detect changes in its total length.

These receptors send an afferent impulse to the spinal cord, where a direct synapse is produced with the motor neuron. The latter emits the efferent signal back to the muscle, which allows its contraction. As you can see, this is a very simple circuit: it has to be so, because the proximity of the structures involved means that the osteotendinous reflexes are produced so quickly.

The medical importance of the osteotendinous reflexes in Medicine

At this point, it should be noted that there are several conditions that can be suspected by the patient's osteotendinous reflexes. On the one hand, hyperreflexia refers to a pathological situation in which the individual suffers hyperactive or repeated reflexes over time (clonic). (clonic).

Apart from muscle spasms, autonomic hyperreflexia causes changes in heart rate, excessive sweating, high Blood Pressure and changes in skin color. The most common cause of this clinical entity is a spinal cord injury, although it can also occur due to certain syndromes, medication side effects or after severe head trauma.

On the other hand, hyporeflexia and areflexia are events in which the muscle does not produce any response to the application of force.. It is a situation that reflects a failure or interruption in the reflex arc, either in the efferent or afferent nerve fiber or, on the other hand, evidence of conditions in the patient such as hypothyroidism, blood electrolyte disturbances or myopathies.

The scale of the osteotendinous reflexes

The osteotendinous reflexes are quantified in the clinic when a nervous or neuromuscular pathology is suspected in the patient.. To carry out this type of test, the muscular structure to be analyzed must be in a neutral position, but before that, the professional must locate the tendon associated with the musculature (to do so, the patient must flex the muscle).

Once the structure has been found, a sudden and rapid force is applied to the relaxed tendon areaThis should result in a rapid and involuntary muscle contraction, or in other words, the osteotendinous reflex that concerns us here. This can be assessed in the following categories:

0= no response on the part of the muscle and is always considered a pathological situation. 1 (+)= a slight but evident muscular response. There are traces of response or a complete response can be promoted with repetitions of the stimulus. It may be normal or indicative of a neuromuscular pathology. 2 (+)= a rapid muscle contraction response. Enter normal. 3 (+)= a very forceful contraction response. May be normal or indicate pathology on the other side of the spectrum. 4 (+)= application of force always elicits repeated reflexes (clonic). This is an abnormal situation in all cases and indicates a clear mismatch at the nervous level.

Whether an osteotendinous reflex 1 to 3 is normal or abnormal depends on its previous status, i.e. what results the patient obtained in the past with respect to the same tests. A more accurate diagnosis can be reached based on the performance of other tests that evaluate muscle tone, contraction strength and other possible pathological evidence..

It should also be noted that the outcome of these tests is subjective, as it depends on the perception of the healthcare professional and the tests he/she has performed in the past. It is not so important for a physician to label one reflex as 2 and another as 2+, but to date the difference in response of the osteotendinous reflexes in different parts of the body of the same patient. The absence (or decrease) of a reflex in one part of the arm and the normality of the same in the analogous limb indicates that there is a problem, for example.

A multitude of contraptions can be used to cause slight elongation of the muscle fiber to be tested, but small specialized hammers are always recommended for the test. These come in 3 types according to their shape: triangular (Taylor), T-shaped (Tromner) and circular (Queen square).. All are effective in eliciting reflexes, but it is recommended to avoid using the Taylor model in patients with hyperreflexia, as it is the least effective in promoting osteotendinous reflexes.

On the other hand, although it sounds strange, sometimes the use of the fingers is also used (very useful in patients with hyperreflexia) and even the edge of a smartphone can be used. It is much more important to find the point where the pressure should be exerted than the material with which it is performed.

Summary

The world of the osteotendinous reflexes is very complex, since it is necessary to have clear a series of concepts of neuromuscular physiology that only those specialized in the subject can acquire. If we want you to have a clear idea, this is the following: the reflex arc of the osteotendinous reflexes is composed of 2 neurons, one afferent and the other efferent, which communicate in the integrating center. The response to the pressure stimulus is very fast and can be quantified numerically.

The fact that the patient presents hypo- or hyperreflexia is always indicative of a pathology, either in the neurons of the circuit or in the internal spinal cord itself. Detecting these abnormalities is essential to put in place accurate diagnostic mechanisms and to start treatment as soon as possible. Therefore, osteotendinous reflexes are extremely important in medical practice at the neuromuscular level.

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