Improper functioning of the knee reflex indicates serious disturbances in the functioning of the body. To diagnose the disease in the early stages, you should know what your reaction to a hammer blow under your knee indicates. Let's look at this in the 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 the nerves. The brain has a standard scheme for transmitting impulses along the path. In cases where an immediate response is required, the reflex passes through the spinal cord. This reaction occurs, for example, if you step on a needle, then your leg jerks back sharply. If the reflex went through the brain, there would definitely be a delay in the process, which can be dangerous for the life of the body.
So, a reflex is an instant response to an external stimulus; it is coordinated by the nervous system. And its path is called a reflex arc. The irritation signal is transmitted via afferent nerves to efferent centers in the spinal cord. It is then transmitted to the muscles, which contract. The absence of reflexes is a symptom of a disease of the muscles, nervous system, brain, or a special emotional state. Vital body processes also operate reflexively, such as the production of saliva when food is consumed.
How to trigger the knee reflex?
The occurrence of the knee reflex is due to the fact that when a medical hammer hits the quadriceps tendon, it contracts. This contraction causes the leg to straighten. The blow must be delivered directly under the kneecap, because the quadriceps extensor tendon is attached to the beginning of the tibia. It is not necessary to hit with force, the main thing is that the muscles are as relaxed as possible. You can cross one leg over the other, then when the patellar reflex occurs, it will jerk upward.
What if you need other methods?
If the traditional method does not work, there are several other methods for demonstrating the knee reflex:
- The person should be seated on a chair with their toes touching the floor and their legs bent at an angle slightly greater than 90 degrees. The blow must be applied from top to bottom over the retracted 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 your legs hang in a relaxed state;
- There is also a method when the patient is lowered onto his back with his knees stacked one on top of the other.
There are times when the patient is physically unable to sufficiently relax the limb being examined. Then specialists use methods of disinhibition of the knee reflex, for example, the techniques of Jendrassik and Shvetsov. The patient should also breathe deeply or solve simple mathematical problems out loud.
What do disturbances in the knee reflex indicate?
Muscles contract in a similar way on the upper pair of limbs and elsewhere in the body. But the significance 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 can a healthy person not have a knee reflex; in this case, most likely, a childhood illness damaged his work. In the presence of diseases, it may be absent or, on the contrary, excessively intensified. This is explained by the fact that the center of the knee reflex is located in the lumbar spinal cord, or 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 reflex. 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 the knee reflex indicates significant damage to the nervous system. Also, the reflex may disappear in epileptics after a seizure, after using a tourniquet, during deep anesthesia or after heavy muscle strain. Only a specialist can make an accurate diagnosis.
Why are neurological tests especially important for athletes?
In general, athletes are no more susceptible to illness than the general public, but they do have a higher risk of injury.
Marina:
Sports can be associated with injuries to the head, peripheral nerves, and spine. Therefore, athletes need to undergo regular neurological examinations. An examination by a neurologist allows you to identify abnormalities in the state of the nervous system earlier and take appropriate measures.
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In many cases, serious diseases of the nervous system can be detected in the early stages even with the help of such seemingly simple tests. It is important to listen to your own feelings and not be afraid to consult a doctor.
What is a reflex arc?
The knee reflex occurs due to its reflex arc. Just as there is significant disruption to the overall functioning of a machine due to the presence of a damaged part, the human body is similarly unable to function when something is not working correctly. A reflex arc is the path of a signal from the receptor that receives it to the organ that responds to it. It is also called the neural arch. This name is explained by the fact that the knee reflex occurs due to impulses in the nerves that travel 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 the transmission of irritation.
Next, the neurological status is studied
Assessment of neurological status is the most effective way to monitor the state of the human nervous system.
Study of the functions of the cranial nerves (cranial nerves).
There are 12 of them in total. They are responsible for smell, vision, facial expressions, hearing, vestibular apparatus, sensory and motor functions of the tongue and head. For this diagnosis, the doctor asks the patient to follow the movement of the hammer with his eyes, show his tongue, and close his eyes.
Study of reflex-motor functions, sensitivity and functions of the ANS.
This is where a hammer comes in handy: by lightly hitting certain points, the doctor assesses the symmetry and vivacity of tendon reflexes. To study the coordination of movements, the doctor will ask you to stretch your arms, twist your palms, touch the tip of your nose with your finger, and stand with your legs aligned in one line. By applying non-painful point touches to the limbs and body with the base of the hammer, the doctor checks sensitivity.
The doctor will also ask you to stretch out your arms, twist your palms and touch the tip of your nose with your finger, and stand on one leg to study your ability to navigate in space and coordinate movements. This way the doctor will evaluate the functioning of the vestibular apparatus.
Study of higher brain functions.
At this stage, the doctor excludes psychological disorders and disorders of brain function by asking questions of the patient and observing behavior during the appointment.
The doctor determines what kind of research to conduct for each specific patient, based on the patient’s symptoms and complaints.
All tests are painless and will not cause any discomfort to the patient, but on the contrary, they are of interest to children!
In addition to the main tests, additional instrumental or laboratory examinations may be prescribed, for example, electroencephalography (EEG) or rheoencephalography (REG).
How does the knee jerk reflex arc work?
The arc of the knee reflex involves three sections of the back, from the second to the fourth. In this case, the fourth department is the most important in the process.
The reflex arc of the knee reflex has five components:
- Receptors. They receive the stimulus signal and become excited in response. These are the ends of axons or bodies located in epithelial cells. Receptors are found everywhere in the human body, in organs, in the skin, they make up the sense organs;
- The nerve fiber is sensitive, afferent or centripetal. It transmits the signal to the center. Neuronal bodies are located outside the central nervous system, namely near the brain and in the nerve ganglia near the spinal cord.
- The nerve center is the place where the signal is transmitted from afferent neurons to efferent ones. The centers of efferent neurons are located in the spinal cord.
- The nerve fiber is motor, centrifugal or efferent. As the name suggests, excitation along it goes from the central nervous system to a specific organ. The efferent fiber is an axon (or a long process) of a centrifugal neuron.
- Effector. An organ that responds to stimulation of a specific receptor. This is a muscle that contracts after processing a signal from the center, a gland that exudes juice due to nervous excitement, and more.
What other neurological tests are there?
Marina Kazakova
pulmonologist
During a standard examination, the doctor assesses the patient’s consciousness, orientation in space, time, and his own personality. For example, it may ask the following questions: where are you now, what year is it, what is your name.
The doctor also looks at the size of the pupils, their symmetry, and reaction to light. The functions of the cranial nerves are assessed: you may be asked to frown, smile, or stick out your tongue. The neurologist pays attention to tendon reflexes, their symmetry, arm strength, and symptoms of meningitis.
The doctor also checks for the presence of pathological reflexes, for example, in the foot. This test shows the reflex of the flexor muscles of the foot and toes: if, in response to their rapid stretching, the toes seem to “nod”, the reaction is considered increased and the neurologist may prescribe additional tests.
Many tests are carried out depending on the patient's complaints and the suspected problem.
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Peter:
All these sometimes strange rituals help the specialist evaluate how the nervous system functions.
How does the impulse move during the knee reflex?
To study the knee reflex in detail, its stages should be studied. The passage of nerve impulses during the knee reflex occurs as follows:
- hitting the tendon under the knee with a hammer causes this tendon to stretch, therefore, a receptor potential arises in the corresponding receptors;
- An action potential arises in the neuronal long process. In the spinal cord it is chemically transmitted to the motor neuron;
- the axon of the efferent neuron serves as a signal path to the gastrocnemius muscle;
- due to muscle contraction, the leg twitches.
Now you know how the reflex works and for what purposes it is diagnosed.
First of all, the doctor asks the parent about the patient’s life history.
How the pregnancy and childbirth proceeded, what developmental features and illnesses the child or his relatives had, when he spoke and walked, whether he slept soundly, what behavior is typical of the child and much, much more detailed information is needed to draw a conclusion.