Knee-jerk reflex and its meaning. Arc of the knee reflex

Incorrect work of the knee reflex indicates serious disorders of the body. To diagnose the disease in the early stages, you should know what your reaction to the impact of the hammer under the knee tells you. Consider this in the article.

Admission of information from outside and its translation through the body: the muscles, organs, spinal cord and brain is ensured by the stable operation of nerves. The standard scheme for impulse transmission on the way is the brain. In cases where an immediate reaction is required, the reflex passes through the spinal cord. This reaction occurs, for example, if you step on the needle, then the leg is sharply pulled back. If the reflex were to go through the brain, there would definitely be a delay in the process, which is dangerous for the life of the organism.

Knee-jerk reflex and its meaning. Arc of the knee reflex

So, the reflex is an instant response to an external stimulus, it is coordinated by the nervous system. And his way is called a reflex arc.
The stimulus signal is transmitted by afferent nerves to the efferent centers in the spinal cord. Then it is transferred to the muscles, which are contracted. Absence of reflexes is a symptom of a disease of the muscles, nervous system, brain, special emotional state. Vital processes of the body also work reflexively, for example, the saliva supply when eating food.

How to cause a knee jerk?

The origin of the knee reflex is due to the fact that during the impact of the medical malleus on the quadriceps tendon it contracts. This reduction causes the leg to straighten. The impact must be applied exactly under the knee cap, because the tendon of the unbending quadriceps muscle is fixed at the beginning of the tibia. It is not necessary to beat with force, the main thing is that the muscles are as relaxed as possible.
You can throw one leg to the other, then when the patellar reflex arises, it will twitch upward.

What if I need other methods?

In the event that the traditional method does not work, there are several other techniques for manifesting the knee reflex:

• The person should be put on a chair so that the toes rest against the floor, and the legs bend at an angle of slightly more than 90 degrees. The blow must be applied from above downward over the protruded patella. As a result, the patella rises;
• The knee of the necessary leg should be placed on top of the second knee;
• You can apply a high seat so that your legs hang in a relaxed state;
• There is also a way when the patient is lowered onto the back with one knee in the other.

There are times when a patient can not physically relax the subject's limb sufficiently. Then the specialists apply the methods of knee-jerk disinhibition, for example, the techniques of Endrassic and Shvetsov. Also, the patient should breathe deeply or aloud solve simple mathematical examples.

What are the violations in the work of the knee reflex?

Muscles contract in a similar manner on the upper pair of limbs and in other parts of the body. But the value of the knee reflex is that its violation is considered an important symptom of abnormalities in the functioning of the brain and spinal cord. The arc of the knee reflex is constant. Only in rare cases, a healthy person may not have a knee reflex, and, most likely, a child's disease has damaged his work. In the presence of diseases, it may be absent or, on the contrary, excessively amplified. This is because the center of the knee reflex is located in the lumbar spinal cord, or rather in the II-IV segment. For some diseases, there are specific deviations in the manifestation of the knee reflex. For example, cerebral lesions cause a pendulum-like knee-jerk reflex. An amplified reflex may indicate a form of neurosis. On the contrary, the reduced form of the reflex is a sign of infection or intoxication of the body. A complete absence of the knee reflex indicates a significant lesion of the nervous system. Also, the reflex can disappear in epileptics after a seizure, after using a tourniquet, during a deep anesthetic, or after a heavy muscular load. Only an expert can make an accurate diagnosis.

What is a reflex arc?

The knee reflex is due to its reflex arc. Like a significant disruption in the overall working process of the mechanism due to the presence of the damaged part, the human body can not function in the same way when something is not working properly.
The reflex arc is the path of the signal from the receptor that received it to the organ that reacts to it. It is also called a nerve arc. This name is explained by the fact that the knee-jerk reaction occurs due to impulses in the nerves, which overcome a certain path. The reflex arc consists of chains of neurons that are formed from intercalary, receptor and effector neurons. They themselves and their processes create a path for transmission of irritation.

What are the types of reflex arcs?

The peripheral nervous system has two types of reflex arcs:

• Those that signal the internal organs;
• Those that are related to skeletal muscles.

How does the reflex arc of the knee reflex work?

The arc of the knee reflex involves three parts of the back, from the second to the fourth. In this case, the fourth department is most important in the process.

The reflex arc of the knee reflex has five components:

1. Receptors. They receive the stimulus signal and are reactivated in response. These are the ends of axons or the corpuscles in the cells of the epithelium. Receptors are found everywhere in the human body, in organs, in the skin, of which sense organs are composed;
2. The nerve fiber is sensitive, afferent or centripetal. It transmits the signal to the center. Neural bodies are located outside the central nervous system, namely near the brain and in the nerve nodes near the spinal cord.
3. The nerve center is the place where the signal is transmitted from the afferent neurons to the efferent. The centers of efferent neurons are in the spinal cord.
4. Nerve fibers are motor, centrifugal or efferent. As the name implies, the excitement on it goes from the central nervous system to a specific organ. The efferent fiber itself is an axon (or a long process) of a centrifugal neuron.
5. The effector. An organ that exhibits a reaction to the irritation of a particular receptor. It is a muscle that contracts after processing the signal from the center, iron, which exudes juice due to nervous excitement, and more.

How does the impulse move at the knee reflex?

For a detailed study of the knee reflex, its stages should be studied. The passage of nerve impulses in the knee reflex occurs as follows:

• A hammer blow to the tendon under the knee causes this tendon to stretch, hence the receptor potential arises in the corresponding receptors;
• In the neural long process, the potential of action arises. In the spinal cord, it is chemically transmitted to the motor neuron ;
• The axon of the efferent neuron serves as a signal to the gastrocnemius muscle;
• Because of the contraction of the muscle, the leg twitches.

Now you know how the reflex works, and for what purposes it is used to diagnose it.