Incorrect operation of the knee reflex indicates serious violations of the body. To diagnose the disease in the early stages, you should know what your reaction to the hammer blow under the knee indicates. Consider this in an article.
The reception of information from the outside and its transmission throughout the body: through the muscles, organs, spinal cord and brain, is ensured by the stable functioning of nerves. The standard pattern of transmission of impulses along the way is the brain. In cases where an immediate reaction is required, the reflex passes through the spinal cord. Such a reaction occurs, for example, if you step on the needle, then the leg jerks sharply. If the reflex went through the brain, there would definitely be a delay in the process, which can be life threatening.
Man's knee-jerk reflex and its significance. 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 path is called the reflex arc.
The signal of irritation is transmitted using afferent nerves to the efferent centers in the spinal cord. Then it is transmitted to muscles that contract. The absence of reflexes is a symptom of a disease of the muscles, nervous system, brain, and special emotional state. Vital processes of the body also work reflexively, for example, the supply of saliva when eating food.
How to cause a knee jerk?
The occurrence of a knee reflex is due to the fact that during the impact of a medical malleus on the quadriceps tendon, it contracts. This contraction makes the leg straighten. The blow must be applied exactly under the patella, because the tendon of the extensor quadriceps 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 foot on the other, then when a patellar reflex occurs, it will twitch up.
What if other methods are needed?
If the traditional method does not work, there are several methods for the manifestation of the knee reflex:
- the person should be seated on a chair so that the toes rest on the floor, and the legs are bent at an angle of slightly more than 90 degrees. The blow must be applied from top to bottom over the pulled patella. As a result, the patella rises;
- the knee of the required leg must be placed on top of the second knee;
- you can use a high seat so that the legs hang in a relaxed state;
- There is also a method where the patient is lowered onto his back with one knee resting on top of the other.
There are times when the patient is physically unable to sufficiently relax the examined limb. Then specialists apply methods of disinhibition of the knee reflex, for example, the techniques of Endrassik and Shvetsov. Also, the patient should breathe deeply or solve simple mathematical examples aloud.
What are the violations in the work of the knee reflex?
Muscles contract in a similar way on the upper pair of limbs and in other parts of the body. But the importance of the knee reflex is that its violation is considered an important symptom of abnormalities in the work of the brain and spinal cord. The arc of the knee jerk is constant. Only in rare cases, a healthy person may not have a knee-jerk reaction, and most likely, a childhood illness has damaged his work. In the presence of diseases, it may be absent or, conversely, excessively amplified. This is because the center of the knee reflex is located in the lumbar spinal cord, and more precisely 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 reaction. An enhanced reflex may indicate a form of neurosis. On the contrary, a reduced form of the reflex is a sign of infection or intoxication of the body. The complete absence of a knee reflex indicates a significant damage to the nervous system. Also, the reflex can disappear in epileptics after a seizure, after using a tourniquet, during deep anesthesia or after severe muscle load. Only a specialist can make an accurate diagnosis.
What is a reflex arc?
The knee-jerk reflex is due to its reflex arch. Like a significant violation of the overall working process of the mechanism due to the presence of a damaged part, the human body cannot function exactly the same way when something does not work properly.
Reflex arc is the signal path from the receptor that received it to the organ that responds to it. It is also called the neural arc. This name is explained by the fact that the knee jerk occurs due to impulses in the nerves that overcome a certain path. The reflex arc consists of chains of neurons that are formed from intercalated, receptor, and effector neurons. They themselves and their processes create a path for the transmission of irritation.
What are the types of reflex arcs?
The peripheral nervous system has two types of reflex arcs:
- those that provide signals to internal organs;
- those related to skeletal muscle.
How does the reflex arch of the knee jerk work?
The knee-jerk arch involves three parts of the back, from the second to the fourth. Moreover, the fourth section is most important in the process.
The reflex arch of the knee reflex has five components:
- Receptors. They receive a stimulus signal and are excited in response. These are the ends of axons or those located in the cells of the body epithelium. Receptors are everywhere in the human body, in organs, in the skin, of which the sensory organs are composed;
- The nerve fiber is sensitive, afferent, or centripetal. It transmits a 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.
- Nerve center - a place where the signal is transmitted from afferent efferent neurons. The centers of efferent neurons are located in the spinal cord.
- Nerve fiber is motor, centrifugal or efferent. As the name implies, the excitement from it goes from the central nervous system to a specific organ. An efferent fiber is an axon (or a long process) of a centrifugal neuron.
- Effector. An organ that responds to irritation of a particular receptor. This is a muscle that contracts after processing a signal from the center, iron that exudes juice due to nervous excitement, and more.
How does the impulse move with a knee jerk?
For a detailed study of the knee reflex, its stages should be studied. The passage of nerve impulses with a knee reflex occurs as follows:
- hammer blow to the tendon under the knee causes this tendon to stretch, therefore, the receptor potential arises in the corresponding receptors;
- in a long neural process, an action potential 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 calf muscle;
- due to muscle contraction, the leg twitches.
Now you know how the reflex works, and for what purpose it is diagnosed.